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Jonathan Nieder 03-19-2012 09:26 PM

document symbols
 
Russ Allbery wrote:

> I'm therefore including here the complete
> SGML source of that section not in diff format, followed by the diff of
> everything *outside* of that section. I think this will be easier to
> review.

Thanks! I would have preferred a diff since it shows the text that is
being replaced, too, but let's go with this for a first pass.

[...]
> <p>
> If a package contains a binary or library which links to a
> shared library, we must ensure that, when the package is
> installed on the system, all of the libraries needed are also
> installed.

This text is carried over from before and contains a requirement I
never noticed before. Suppose my package contains two binaries:
maintool and side-tool. The latter is not very important and links
to libbiglibrary. I might be tempted to make the dependency by my
package on libbiglibrary a Recommends instead of a Depends. The above
says I must not.

Intentional? It seems like good policy, anyway.

> These dependencies must be added to the binary
> package when it is built, since they may change

This means packages must not hard-code library dependencies. It
also seems like good policy, but I suspect it would render packages
such as chromium that use dlopen() and hard-code the corresponding
library name in dependencies RC-buggy.

What about libraries like glib (assuming one only uses old symbols)
that are never supposed to change soname?

[...]
> To allow these dependencies to be constructed, shared libraries
> must provide either a <file>symbols</file> file or
> a <file>shlibs</file> file, which provide information on the
> package dependencies required to ensure the presence of this
> library.

Subject/verb agreement: s/provide/provides/

Clarity: s/this library/interfaces provided by this library/

> <p>
> These two mechanisms differ in the degree of detail that they
> provide. A <file>symbols</file> file documents every symbol
> that is part of the library ABI and, for each, the version of
> the package in which it was introduced.

Maybe, since minimal-version is not always the version in which the
symbol was introduced:

and, for each, a minimal version of the library needed to use
that symbol, which is typically the version of the package in
which it was introduced.

[...]
> <file>shlibs<file> files also have a flawed representation of
> library SONAMEs, making it difficult to use <file>shlibs</file>
> files in some unusual corner cases.

I'm not sure what this passage is referring to. Can you say more?
(Maybe in a footnote.)

[...]
> udebs
> must also use <file>shlibs</file>, since the udeb infrastructure
> does not use <file>symbols</file>.

To avoid confusion it might be worth forbidding symbols files in
udebs, or at least symbols files without a corresponding shlibs file
accompanying them.

[...]
> If you have
> multiple binary packages, you will need to
> call <prgn>dpkg-shlibdeps</prgn> on each one which contains
> compiled libraries or binaries, using the <tt>-T</tt> option
> to the <tt>dpkg</tt> utilities to specify a
> different <file>substvars</file> file for each binary
> package.<footnote>

An alternative is to clear substvars between builds of different
binary packages.

[...]
> loads <tt>libbar</tt>. A package should depend on the
> libraries it directly uses, but not the libraries it
> indirectly uses.

Pedantry: what if my package uses the same library both directly and
indirectly? "but not the libraries it only uses indirectly" would
avoid that question.

> There are two types of ABI changes: ones that are
> backward-compatible and ones that are not. An ABI change is
> backward-compatible if any binary was linked with the previous
> version of the shared library will still work correctly with
> the new version of the shared library. Adding new symbols to
> the shared library is a backward-compatible change. Removing
> symbols from the shared library is not.

If I remove a symbol that was documented to be private or change
the behavior of a function when given invalid arguments, is that a
backward-compatible change?

If I add change the implementation in such a way that the library
becomes so large that some large programs cannot use it any more, is
that a backward-incompatible change?

[...]
> <file>symbols</file> files for a shared library are normally
> provided by the shared library package, but there are
> several override paths that are checked first in case that
> information is wrong or missing.

It's not obvious at first how the two clauses of this sentence relate
to each other. (Why would which package provides the file and its
path necessarily relate to each other?) Mentioning that this is a
control file in the package (i.e., adding "as a control file" before
"by the shared library package") might help.

[...]
> Packages using only <tt>compress</tt> would then get a
> dependency of <tt>zlib1g (>= 1:1.1.4)</tt>, but packages
> using <tt>compressBound</tt> would get a dependency
> of <tt>zlib1g (>= 1:1.2.0)</tt>.

s/of /on /g

[...]
> +++ b/policy.sgml
> @@ -848,10 +848,11 @@
> Among those files are the package maintainer scripts
> and <file>control</file>, the <qref id="binarycontrolfiles">binary
> package control file</qref> that contains the control fields for
> - the package. Other control information files
> + the package. Other control information files include

Unrelated change. The patch would have been easier to review if this
were a separate commit, which could have gone straight to master since
it doesn't change the output.

The rest looks good from a quick glance. Thanks again for writing
this.

Jonathan


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Jonathan Nieder 03-20-2012 08:28 PM

document symbols
 
Julien Cristau wrote:
> On Mon, Mar 19, 2012 at 17:26:04 -0500, Jonathan Nieder wrote:

>> What about libraries like glib (assuming one only uses old symbols)
>> that are never supposed to change soname?
>
> What about them?

I wanted to make sure that forbidding hard-coded dependencies on them
is intentional. It seems like a good choice to me, but it should be a
deliberate choice (and it does not seem obvious to me that a patch
documenting symbols would automatically do that).

>> [...]
>>> <file>shlibs<file> files also have a flawed representation of
>>> library SONAMEs, making it difficult to use <file>shlibs</file>
>>> files in some unusual corner cases.
>>
>> I'm not sure what this passage is referring to. Can you say more?
>> (Maybe in a footnote.)
>
> libfooN.shlibs says 'libfoo N' not the actual SONAME, so if the SONAME
> doesn't match one of the two expected formats (libfoo-N.so or
> libfoo.so.N) it can't be represented.

Thanks. Sounds like good text for a footnote.

[...]
>> To avoid confusion it might be worth forbidding symbols files in
>> udebs, or at least symbols files without a corresponding shlibs file
>> accompanying them.
>
> That makes no sense. udebs don't have those files, when building an
> udeb the dependency information is read from the shlibs files of the
> debs corresponding to the libraries you depend on.

Oh, good catch. Russ's text said:

<file>symbols</file> files are therefore recommended for most
shared library packages since they provide more accurate
dependencies. For most C libraries, the additional detail
required by <file>symbols</file> files is not too difficult to
maintain. However, maintaining exhaustive symbols information
for a C++ library can be quite onerous, so <file>shlibs</file>
files may be more appropriate for most C++ libraries. udebs
must also use <file>shlibs</file>, since the udeb infrastructure
does not use <file>symbols</file>.

which sounded like it was saying that most shared libraries should
provide symbols files but udebs should not since the infrastructure
does not support it.

If I understand you correctly, the actual rule would be:

- symbols files are always recommended

- the deb corresponding to a shared library udeb must provide a
shlibs file to support udeb infrastructure

- udebs provide neither shlibs nor symbols files

[...]
>>> If you have
>>> multiple binary packages, you will need to
>>> call <prgn>dpkg-shlibdeps</prgn> on each one which contains
>>> compiled libraries or binaries, using the <tt>-T</tt> option
>>> to the <tt>dpkg</tt> utilities to specify a
>>> different <file>substvars</file> file for each binary
>>> package.<footnote>
>>
>> An alternative is to clear substvars between builds of different
>> binary packages.
>
> Who does that?

I did before I saw this patch, in a package not yet proposed for
upload to Debian. Should I be ashamed?

>>> There are two types of ABI changes: ones that are
>>> backward-compatible and ones that are not. An ABI change is
>>> backward-compatible if any binary was linked with the previous
>>> version of the shared library will still work correctly with
>>> the new version of the shared library. Adding new symbols to
>>> the shared library is a backward-compatible change. Removing
>>> symbols from the shared library is not.
>>
>> If I remove a symbol that was documented to be private or change
>> the behavior of a function when given invalid arguments, is that a
>> backward-compatible change?
>>
>> If I add change the implementation in such a way that the library
>> becomes so large that some large programs cannot use it any more, is
>> that a backward-incompatible change?
>
> I'm not sure policy should go into such details.

Sorry for the lack of clarity. I never meant to suggest that policy
should speak to these cases directly. That would be insane, and among
other consequences it would result in a very long policy manual.

What I was trying to hint at is that the above definition gives the
wrong answer to both questions.

> And anyway, that's
> answered by the previous sentence (an incompatible change is one that
> breaks reverse deps). The last two are simple examples.

The definition says a change is backward-compatible when "any binary
[that] was linked with the previous version of the shared library will
still work correctly with the new version of the shared library". If
I understand it correctly, that means that the answer to the first
question is "no" (a binary using private symbols is still a binary)
and the answer to the second question is "yes" (a binary whose process
image barely fits in address space is still a binary).

I believe the definition would need a word like "reasonable" before
"binary" to be accurate.

Thanks for your help,
Jonathan


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Jonathan Nieder 07-09-2012 03:37 AM

document symbols
 
Russ Allbery wrote:

> Here is a new proposed patch that incorporates the feedback to date with
> some other, substantial changes.

Thanks again for that. Here's an updated version of the same patch
incorporating feedback found downthread.

It is unfortunately a little noisy because there are some
whitespace-only changes mixed in. If someone has the time to make
one, a patch that just makes the indentation and rewrapping changes
that could be quickly applied to master would be a nice way to
simplify the review.

I'll reply with an interdiff relative to the last version of the
patch.

Thoughts welcome, as always.
Jonathan
diff --git c/policy.sgml w/policy.sgml
index 52dbb26a..50ae756c 100644
--- c/policy.sgml
+++ w/policy.sgml
@@ -848,10 +848,11 @@
Among those files are the package maintainer scripts
and <file>control</file>, the <qref id="binarycontrolfiles">binary
package control file</qref> that contains the control fields for
- the package. Other control information files
- include <qref id="sharedlibs-shlibdeps">the <file>shlibs</file>
- file</qref> used to store shared library dependency information
- and the <file>conffiles</file> file that lists the package's
+ the package. Other control information files include
+ the <qref id="sharedlibs-symbols"><file>symbols</file> file</qref>
+ or <qref id="sharedlibs-shlibdeps"><file>shlibs</file> file</qref>
+ used to store shared library dependency information and
+ the <file>conffiles</file> file that lists the package's
configuration files (described in <ref id="config-files">).
</p>

@@ -5493,17 +5494,29 @@ Replaces: mail-transport-agent
be placed in a package named
<package><var>libraryname</var><var>soversion</var></package>,
where <var>soversion</var> is the version number in
- the <tt>SONAME</tt> of the shared library.
- See <ref id="shlibs"> for detailed information on how to
- determine this version. Alternatively, if it would be confusing
- to directly append <var>soversion</var>
- to <var>libraryname</var> (if, for example, <var>libraryname</var>
- itself ends in a number), you should use
+ the <tt>SONAME</tt> of the shared library. Alternatively, if it
+ would be confusing to directly append <var>soversion</var>
+ to <var>libraryname</var> (if, for
+ example, <var>libraryname</var> itself ends in a number), you
+ should use
<package><var>libraryname</var>-<var>soversion</var></package>
instead.
</p>

<p>
+ To determine the <var>soversion</var>, look at
+ the <tt>SONAME</tt> of the library, stored in the
+ ELF <tt>SONAME</tt> attribute. it is usually of the
+ form <tt><var>name</var>.so.<var>major-version</var></tt> (for
+ example, <tt>libz.so.1</tt>). The version part is the part
+ which comes after <tt>.so.</tt>, so in that example it
+ is <tt>1</tt>. The soname may instead be of the
+ form <tt><var>name</var>-<var>major-version</var>.so</tt>, such
+ as <tt>libdb-5.1.so</tt>, in which case the name would
+ be <tt>libdb</tt> and the version would be <tt>5.1</tt>.
+ </p>
+
+ <p>
If you have several shared libraries built from the same source
tree, you may lump them all together into a single shared
library package provided that all of their <tt>SONAME</tt>s will
@@ -5538,9 +5551,8 @@ Replaces: mail-transport-agent
linked against the old shared library. Correct versioning of
dependencies on the newer shared library by binaries that use
the new interfaces is handled via
- the <qref id="sharedlibs-shlibdeps"><tt>shlibs</tt>
- system</qref> or via symbols files (see
- <manref name="deb-symbols" section="5">).
+ the <qref id="sharedlibs-depends"><tt>symbols</tt>
+ or <tt>shlibs</tt> system</qref>.
</p>

<p>
@@ -5809,361 +5821,870 @@ Replaces: mail-transport-agent
</p>
</sect>

- <sect id="sharedlibs-shlibdeps">
- <heading>Dependencies between the library and other packages -
- the <tt>shlibs</tt> system</heading>
+ <sect id="sharedlibs-depends">
+ <heading>Dependencies between the library and other
+ packages</heading>

<p>
If a package contains a binary or library which links to a
- shared library, we must ensure that when the package is
- installed on the system, all of the libraries needed are
- also installed. This requirement led to the creation of the
- <tt>shlibs</tt> system, which is very simple in its design:
- any package which <em>provides</em> a shared library also
- provides information on the package dependencies required to
- ensure the presence of this library, and any package which
- <em>uses</em> a shared library uses this information to
- determine the dependencies it requires. The files which
- contain the mapping from shared libraries to the necessary
- dependency information are called <file>shlibs</file> files.
- </p>
-
- <p>
- When a package is built which contains any shared libraries, it
- must provide a <file>shlibs</file> file for other packages to
- use. When a package is built which contains any shared
- libraries or compiled binaries, it must run
- <qref id="pkg-dpkg-shlibdeps"><prgn>dpkg-shlibdeps</prgn></qref>
- on these to determine the libraries used and hence the
- dependencies needed by this package.<footnote>
- <p>
+ shared library, we must ensure that, when the package is
+ installed on the system, all of the libraries needed are also
+ installed. These dependencies must be added to the binary
+ package when it is built, since they may change based on which
+ version of a shared library the binary or library was linked
+ with even if there are no changes to the source of the binary
+ (for example, symbol versions change, macros become functions or
+ vice versa, or the binary package may determine at compile-time
+ whether new library interfaces are available and can be called).
+ To allow these dependencies to be constructed, shared libraries
+ must provide either a <file>symbols</file> file or
+ a <file>shlibs</file> file, which provides information on the
+ package dependencies required to ensure the presence of
+ interfaces provided by this library. Any package with binaries
+ or libraries linking to a shared library must use these files
+ to determine the required dependencies when it is built. Other
+ packages which use a shared library (for example using
+ <tt>dlopen()</tt>) should compute appropriate dependencies
+ using these files at build time as well.
+ </p>
+
+ <p>
+ The two mechanisms differ in the degree of detail that they
+ provide. A <file>symbols</file> file documents for each symbol
+ exported by a library the minimal version of the package any
+ binary using this symbol will need, which is typically the
+ version of the package in which the symbol was introduced.
+ This permits detailed analysis of the symbols used by a
+ particular package and construction of an accurate dependency,
+ but it requires the package maintainer to track more information
+ about the shared library. A <file>shlibs</file> file, in
+ contrast, only documents the last time the library ABI changed
+ in any way. It only provides information about the library as a
+ whole, not individual symbols. When a package is built using a
+ shared library with only a <file>shlibs</file> file, the generated
+ dependency will require a version of the shared library equal to
+ or newer than the version of the last ABI change. This
+ generates unnecessarily restrictive dependencies compared
+ to <file>symbols</file> files if none of the symbols used by the
+ package have changed. This, in turn, may make upgrades
+ needlessly complex and unnecessarily restrict use of the package
+ on systems with older versions of the shared libraries.
+ </p>
+
+ <p>
+ <file>shlibs<file> files also have a flawed representation of
+ library SONAMEs, making it difficult to use <file>shlibs</file>
+ files in some unusual corner cases.<footnote>
+ libfooN.shlibs says 'libfoo N' instead of the actual SONAME,
+ so if the SONAME doesn't match one of the two expected
+ formats (libfoo-N.so or libfoo.so.N) it can't be represented.
+ </footnote>
+ </p>
+
+ <p>
+ <file>symbols</file> files are therefore recommended for most
+ shared library packages since they provide more accurate
+ dependencies. For most C libraries, the additional detail
+ required by <file>symbols</file> files is not too difficult to
+ maintain. However, maintaining exhaustive symbols information
+ for a C++ library can be quite onerous, so <file>shlibs</file>
+ files may be more appropriate for most C++ libraries. Libraries
+ with a corresponding udeb must also provide <file>shlibs</file>,
+ since the udeb infrastructure does not use <file>symbols</file>.
+ </p>
+
+ <sect1 id="dpkg-shlibdeps">
+ <heading>Generating dependencies on shared libraries</heading>
+
+ <p>
+ When a package that contains any shared libraries or compiled
+ binaries is built, it must run <prgn>dpkg-shlibdeps</prgn> on
+ each shared library and compiled binary to determine the
+ libraries used and hence the dependencies needed by the
+ package.<footnote>
<prgn>dpkg-shlibdeps</prgn> will use a program
like <prgn>objdump</prgn> or <prgn>readelf</prgn> to find
- the libraries directly needed by the binaries or shared
- libraries in the package.
+ the libraries and the symbols in those libraries directly
+ needed by the binaries or shared libraries in the package.
+ </footnote>
+ To do this, put a call to <prgn>dpkg-shlibdeps</prgn> into
+ your <file>debian/rules</file> file in the source package.
+ List all of the compiled binaries, libraries, or loadable
+ modules in your package.<footnote>
+ The easiest way to call <prgn>dpkg-shlibdeps</prgn>
+ correctly is to use a package helper framework such
+ as <package>debhelper</package>. If you are
+ using <package>debhelper</package>,
+ the <prgn>dh_shlibdeps</prgn> program will do this work for
+ you. It will also correctly handle multi-binary packages.
+ </footnote>
+ <prgn>dpkg-shlibdeps</prgn> will use the <file>symbols</file>
+ or <file>shlibs</file> files installed by the shared libraries
+ to generate dependency information. The package must then
+ provide a substitution variable into which the discovered
+ dependency information can be placed.
+ </p>
+
+ <p>
+ If you are creating a udeb for use in the Debian Installer,
+ you will need to specify that <prgn>dpkg-shlibdeps</prgn>
+ should use the dependency line of type <tt>udeb</tt> by adding
+ the <tt>-tudeb</tt> option<footnote>
+ <prgn>dh_shlibdeps</prgn> from the <tt>debhelper</tt> suite
+ will automatically add this option if it knows it is
+ processing a udeb.
+ </footnote>. If there is no dependency line of
+ type <tt>udeb</tt> in the <file>shlibs</file>
+ file, <prgn>dpkg-shlibdeps</prgn> will fall back to the
+ regular dependency line.
+ </p>
+
+ <p>
+ <prgn>dpkg-shlibdeps</prgn> puts the dependency information
+ into the <file>debian/substvars</file> file by default, which
+ is then used by <prgn>dpkg-gencontrol</prgn>. You will need
+ to place a <tt>${shlibs:Depends}</tt> variable in
+ the <tt>Depends</tt> field in the control file of every binary
+ package built by this source package that contains compiled
+ binaries, libraries, or loadable modules. If you have
+ multiple binary packages, you will need to
+ call <prgn>dpkg-shlibdeps</prgn> on each one which contains
+ compiled libraries or binaries, for example using the
+ <tt>-T</tt> option to the <tt>dpkg</tt> utilities to specify a
+ different <file>substvars</file> file for each binary
+ package.<footnote>
+ Again, <prgn>dh_shlibdeps</prgn>
+ and <prgn>dh_gencontrol</prgn> will handle everything except
+ the addition of the variable to the control file for you if
+ you're using <package>debhelper</package>, including
+ generating separate <file>substvars</file> files for each
+ binary package and calling <prgn>dpkg-gencontrol</prgn> with
+ the appropriate flags.
+ </footnote>
+ </p>
+
+ <p>
+ For more details on <prgn>dpkg-shlibdeps</prgn>,
+ see <manref name="dpkg-shlibdeps" section="1">.
+ </p>
+
- </p>
-
- <p>
- We say that a binary <tt>foo</tt> <em>directly</em> uses
- a library <tt>libbar</tt> if it is explicitly linked
- with that library (that is, the library is listed in the ELF
- <tt>NEEDED</tt> attribute, caused by adding <tt>-lbar</tt>
- to the link line when the binary is created). Other
- libraries that are needed by <tt>libbar</tt> are linked
- <em>indirectly</em> to <tt>foo</tt>, and the dynamic
- linker will load them automatically when it loads
- <tt>libbar</tt>. A package should depend on the libraries
- it directly uses, but not the libraries it indirectly uses.
- The dependencies for those libraries will automatically pull
- in the other libraries.
- </p>
+ <p>
+ We say that a binary <tt>foo</tt> <em>directly</em> uses a
+ library <tt>libbar</tt> if it is explicitly linked with that
+ library (that is, the library is listed in the
+ ELF <tt>NEEDED</tt> attribute, caused by adding <tt>-lbar</tt>
+ to the link line when the binary is created). Other libraries
+ that are needed by <tt>libbar</tt> are
+ linked <em>indirectly</em> to <tt>foo</tt>, and the dynamic
+ linker will load them automatically when it
+ loads <tt>libbar</tt>. A package should depend on the
+ libraries it directly uses, but not the libraries it only uses
+ indirectly. The dependencies for the libraries used
+ directly will automatically pull in the indirectly-used
+ libraries. <prgn>dpkg-shlibdeps</prgn> will handle this logic
+ automatically, but package maintainers need to be aware of
+ this distinction between directly and indirectly using a
+ library if they have to override its results for some reason.
+ <footnote>
-
- <p>
A good example of where this helps is the following. We
could update <tt>libimlib</tt> with a new version that
- supports a new graphics format called dgf (but retaining the
- same major version number) and depends on <tt>libdgf</tt>.
- If we used <prgn>ldd</prgn> to add dependencies for every
- library directly or indirectly linked with a binary, every
- package that uses <tt>libimlib</tt> would need to be
- recompiled so it would also depend on <tt>libdgf</tt> or it
- wouldn't run due to missing symbols. Since dependencies are
- only added based on ELF <tt>NEEDED</tt> attribute, packages
- using <tt>libimlib</tt> can rely on <tt>libimlib</tt> itself
- having the dependency on <tt>libdgf</tt> and so they would
- not need rebuilding.
+ supports a new revision of a graphics format called dgf (but
+ retaining the same major version number) and depends on a
+ new library package <package>libdgf4</package> instead of
+ the older <package>libdgf3</package>. If we
+ used <prgn>ldd</prgn> to add dependencies for every library
+ directly or indirectly linked with a binary, every package
+ that uses <tt>libimlib</tt> would need to be recompiled so
+ it would also depend on <package>libdgf4</package> in order
+ to retire the older <package>libdgf3</package> package.
+ Since dependencies are only added based on
+ ELF <tt>NEEDED</tt> attribute, packages
+ using <tt>libimlib</tt> can rely on <tt>libimlib</tt> itself
+ having the dependency on an appropriate version
+ of <tt>libdgf</tt> and do not need rebuilding.
+ </footnote>
+ </p>
+ </sect1>
+
+ <sect1 id="sharedlibs-updates">
+ <heading>Shared library ABI changes</heading>
+
+ <p>
+ Maintaining a shared library package using
+ either <file>symbols</file> or <file>shlibs</file> files
+ requires being aware of the exposed ABI of the shared library
+ and any changes to it. Both <file>symbols</file>
+ and <file>shlibs</file> files record every change to the ABI
+ of the shared library; <file>symbols</file> files do so per
+ public symbol, whereas <file>shlibs</file> files record only
+ the last change for the entire library.
+ </p>
+
+ <p>
+ There are two types of ABI changes: ones that are
+ backward-compatible and ones that are not. An ABI change is
+ backward-compatible if any reasonable program or library that
+ was linked with the previous version of the shared library
+ will still work correctly with the new version of the shared
+ library. Adding new symbols to the shared library is a
+ backward-compatible change. Removing symbols from the shared
+ library is not. Changing the behavior of a symbol may or may
+ not be backward-compatible depending on the change; for
+ example, changing a function to accept a new enum constant not
+ previously used by the library is generally
+ backward-compatible, but changing the members of a struct that
+ is passed into library functions is generally not unless the
+ library takes special precautions to accept old versions of
+ the data structure.
+ </p>
+
+ <p>
+ ABI changes that are not backward-compatible normally require
+ changing the <tt>SONAME</tt> of the library and therefore the
+ shared library package name, which forces rebuilding all
+ packages using that shared library to update their
+ dependencies and allow them to use the new version of the
+ shared library. For more information,
+ see <ref id="sharedlibs-runtime">. The remainder of this
+ section will deal with backward-compatible changes.
+ </p>
+
+ <p>
+ Backward-compatible changes require either updating or
+ recording the <var>minimal-version</var> for that symbol
+ in <file>symbols</file> files or updating the version in
+ the <var>dependencies</var> in <file>shlibs</file> files. For
+ more information on how to do this in the two formats, see
+ <ref id="symbols"> and <ref id="shlibs">. Below are general
+ rules that apply to both files.
+ </p>
+
+ <p>
+ The easy case is when a public symbol is added. Simply add
+ the version at which the symbol was introduced
+ (for <file>symbols</file> files) or update the dependency
+ version (for <file>shlibs</file>) files. But special care
+ should be taken to update dependency versions when the
+ behavior of a public symbol changes. This is easy to neglect,
+ since there is no automated method of determining such
+ changes, but failing to update versions in this case may
+ result in binary packages with too-weak dependencies that will
+ fail at runtime, possibly in ways that can cause security
+ vulnerabilities. If the package maintainer believes that a
+ symbol behavior change may have occurred but isn't sure, it's
+ safer to update the version rather than leave it unmodified.
+ This may result in unnecessarily strict dependencies, but it
+ ensures that packages whose dependencies are satisfied will
+ work properly.
+ </p>
+
+ <p>
+ A common example of when a change to the is required is a
+ function that takes an enum or struct argument that controls
+ what the function does. For example:
+ <example>
+ enum library_op { OP_FOO, OP_BAR };
+ int library_do_operation(enum library_op);
+ </example>
+ If a new operation, <tt>OP_BAZ</tt>, is added,
+ the <var>minimal-version</var>
+ of <tt>library_do_operation</tt> (for <file>symbols</file>
+ files) or the version in the dependency for the shared library
+ (for <file>shlibs</file> files) must be increased to the
+ version at which <tt>OP_BAZ</tt> was introduced. Otherwise, a
+ binary built against the new version of the library (having
+ detected at compile-time that the library
+ supports <tt>OP_BAZ</tt>) may be installed with a shared
+ library that doesn't support <tt>OP_BAZ</tt> and will fail at
+ runtime when it tries to pass <tt>OP_BAZ</tt> into this
+ function.
+ </p>
+
+ <p>
+ Dependency versions in either <file>symbols</file>
+ or <file>shlibs</file> files normally should not contain the
+ Debian revision of the package, since the library behavior is
+ normally fixed for a particular upstream version and any
+ Debian packaging of that upstream version will have the same
+ behavior. In the rare case that the library behavior was
+ changed in a particular Debian revision, appending <tt>~</tt>
+ to the end of the version that includes the Debian revision is
+ recommended, since this allows backports of the shared library
+ package using the normal backport versioning convention to
+ satisfy the dependency.
+ </p>
+ </sect1>
+
+ <sect1 id="sharedlibs-symbols">
+ <heading>The <tt>symbols</tt> system</heading>
+
+ <p>
+ In the following sections, we will first describe where the
+ various <file>symbols</file> files are to be found, then
+ the <file>symbols</file> file format, and finally how to
+ create <file>symbols</file> files if your package contains a
+ shared library.
+ </p>
+
+ <sect2 id="symbols-paths">
+ <heading>The <file>symbols</file> files present on the
+ system</heading>
+
+ <p>
+ <file>symbols</file> files for a shared library are normally
+ provided by the shared library package as a control file,
+ but there are several override paths that are checked first
+ in case that information is wrong or missing. The following
+ list gives them in the order in which they are read
+ by <prgn>dpkg-shlibdeps</prgn> The first one that contains
+ the required information is used.
+ <list>
+ <item>
+ <p><file>debian/*/DEBIAN/symbols</file></p>
+
+ <p>
+ During the package build, if the package itself
+ contains shared libraries with <file>symbols</file>
+ files, they will be generated in these staging
+ directories by <prgn>dpkg-gensymbols</prgn>
+ (see <ref id="providing-symbols">). <file>symbols</file>
+ files found in the build tree take precedence
+ over <file>symbols</file> files from other binary
+ packages.
+ </p>
+
+ <p>
+ These files must exist
+ before <prgn>dpkg-shlibdeps</prgn> is run or the
+ dependencies of binaries and libraries from a source
+ package on other libraries from that same source
+ package will not be correct. In practice, this means
+ that <prgn>dpkg-gensymbols</prgn> must be run
+ before <prgn>dpkg-shlibdeps</prgn> during the package
+ build.<footnote>
+ An example may clarify. Suppose the source
+ package <tt>foo</tt> generates two binary
+ packages, <tt>libfoo2</tt> and <tt>foo-runtime</tt>.
+ When building the binary packages, the contents of
+ the packages are staged in the
+ directories <file>debian/libfoo2</file>
+ and <file>debian/foo-runtime</file> respectively.
+ (<file>debian/tmp</file> could be used instead of
+ one of these.) Since <tt>libfoo2</tt> provides
+ the <tt>libfoo</tt> shared library, it will contain
+ a <tt>symbols</tt> file, which will be installed
+ in <file>debian/libfoo2/DEBIAN/symbols</file>,
+ eventually to be included as a control file in that
+ package. When <prgn>dpkg-shlibdeps</prgn> is run on
+ the
+ executable <file>debian/foo-runtime/usr/bin/foo-prog</file>,
+ it will examine
+ the <file>debian/libfoo2/DEBIAN/symbols</file> file
+ to determine whether <tt>foo-prog</tt>'s library
+ dependencies are satisfied by any of the libraries
+ provided by <tt>libfoo2</tt>. Since those binaries
+ were linked against the just-built shared library as
+ part of the build process, the <file>symbols</file>
+ file for the newly-built <tt>libfoo2</tt> must take
+ precedence over a <file>symbols</file> file for any
+ other <tt>libfoo2</tt> package already installed on
+ the system.
+ </footnote>
+ </p>
+ </item>
+
+ <item>
+ <p>
+ <file>/etc/dpkg/symbols/<var>package</var>.symbols.<var>arch</var></file>
+ and <file>/etc/dpkg/symbols/<var>package</var>.symbols</file>
+ </p>
+
+ <p>
+ Per-system overrides of shared library dependencies.
+ These files normally do not exist. They are
+ maintained by the local system administrator and must
+ not be created by any Debian package.
+ </p>
+ </item>
+
+ <item>
+ <p><file>symbols</file> control files for packages
+ installed on the system</p>
+
+ <p>
+ The <file>symbols</file> control files for all the
+ packages currently installed on the system are
+ searched last. This will be the most common source of
+ shared library dependency information. These are
+ normally found
+ in <file>/var/lib/dpkg/info/*.symbols</file>, but
+ packages should not rely on this and instead should
+ use <tt>dpkg-query --control-path <var>package</var>
+ symbols</tt> if for some reason these files need to be
+ examined.
+ </p>
+ </item>
+ </list>
+ </p>
+
+ <p>
+ Be aware that if a <file>debian/shlibs.local</file> exists
+ in the source package, it will override
+ any <file>symbols</file> files. This is the only case where
+ a <file>shlibs</file> is used despite <file>symbols</file>
+ files being present. See <ref id="shlibs-paths">
+ and <ref id="sharedlibs-shlibdeps"> for more information.
+ </p>
+ </sect2>
+
+ <sect2 id="symbols">
+ <heading>The <file>symbols</file> File Format</heading>
+
+ <p>
+ The following documents the format of
+ the <file>symbols</file> control file as included in binary
+ packages. These files are built from
+ template <file>symbols</file> files in the source package
+ by <prgn>dpkg-gensymbols</prgn>. The template files support
+ a richer syntax that allows <prgn>dpkg-gensymbols</prgn> to
+ do some of the tedious work involved in
+ maintaining <file>symbols</file> files, such as handling C++
+ symbols or optional symbols that may not exist on particular
+ architectures. When writing <file>symbols</file> files for
+ a shared library package, refer
+ to <manref name="dpkg-gensymbols" section="1"> for the
+ richer syntax.
+ </p>
+
+ <p>
+ A <file>symbols</file> may contain one or more entries, one
+ for each shared library contained in the package
+ corresponding to that <file>symbols</file>. Each entry has
+ the following format:
+ </p>
+
+ <p>
+ <example>
+ <var>library-soname</var> <var>main-dependency-template</var>
+ [| <var>alternative-dependency-template</var>]
+ [...]
+ [* <var>field-name</var>: <var>field-value</var>]
+ [...]
+ <var>symbol</var> <var>minimal-version</var>[ <var>id-of-dependency-template</var> ]
+ </example>
+ </p>
+
+ <p>
+ To explain this format, we'll use the the <tt>zlib1g</tt>
+ package as an example, which (at the time of writing)
+ installs the shared
+ library <file>/usr/lib/libz.so.1.2.3.4</file>. Mandatory
+ lines will be described first, followed by optional lines.
+ </p>
+
+ <p>
+ <var>library-soname</var> must contain exactly the value of
+ the ELF <tt>SONAME</tt> attribute of the shared library. In
+ our example, this is <tt>libz.so.1</tt>.<footnote>
+ This can be determined by using the command
+ <example compact="compact">
+ readelf -d /usr/lib/libz.so.1.2.3.4 | grep SONAME
+ </example>
+ </footnote>
+ </p>
+
+ <p>
+ <var>main-dependency-template</var> has the same syntax as a
+ dependency field in a binary package control file, except
+ that the string <tt>#MINVER#</tt> is replaced by a version
+ restriction like <tt>(>= <var>version</var>)</tt> or by
+ nothing if an unversioned dependency is deemed sufficient.
+ The version restriction will be based on which symbols from
+ the shared library are referenced and the version at which
+ they were introduced (see below). In nearly all
+ cases, <var>main-dependency-template</var> will
+ be <tt><var>package</var> #MINVER#</tt>,
+ where <var>package</var> is the name of the binary package
+ containing the shared library. This adds a simple,
+ possibly-versioned dependency on the shared library package.
+ In some rare cases, such as when multiple packages provide
+ the same shared library ABI, the dependency template may
+ need to be more complex.
+ </p>
+
+ <p>
+ In our example, the first line of
+ the <tt>zlib1g</tt> <file>symbols</file> file would be:
+ <example compact="compact">
+ libz.so.1 zlib1g #MINVER#
+ </example>
+ </p>
+
+ <p>
+ Each public symbol exported by the shared library must have
+ a corresponding symbol line, indented by one
+ space. <var>symbol</var> is the exported symbol (which, for
+ C++, means the mangled symbol) followed by <tt>@</tt> and
+ the symbol version, or the string <tt>Base</tt> if there is
+ no symbol version. <var>minimal-version</var> is the most
+ recent version of the shared library that changed the
+ behavior of that symbol, whether by adding it, changing its
+ function signature (the parameters, their types, or the
+ return type), or its behavior in a way that is visible to a
+ caller. <var>id-of-dependency-template</var> is an optional
+ field that references
+ an <var>alternative-dependency-template</var>; see below for
+ a full description.
+ </p>
+
+ <p>
+ For example, <tt>libz.so.1</tt> contains the
+ symbols <tt>compress</tt>
+ and <tt>compressBound</tt>. <tt>compress</tt> has no symbol
+ version and last changed its behavior in upstream
+ version <tt>1:1.1.4</tt>. <tt>compressBound</tt> has the
+ symbol version <tt>ZLIB_1.2.0</tt>, was introduced in
+ upstream version <tt>1:1.2.0</tt>, and has not changed its
+ behavior. Its <file>symbols</file> file therefore contains
+ the lines:
+ <example compact="compact">
+ compress@Base 1:1.1.4
+ compressBound@ZLIB_1.2.0 1:1.2.0
+ </example>
+ Packages using only <tt>compress</tt> would then get a
+ dependency on <tt>zlib1g (>= 1:1.1.4)</tt>, but packages
+ using <tt>compressBound</tt> would get a dependency
+ on <tt>zlib1g (>= 1:1.2.0)</tt>.
+ </p>
+
+ <p>
+ One or more <var>alternative-dependency-template</var> lines
+ may be provided. These are used in cases where some symbols
+ in the shared library should use one dependency template
+ while others should use a different template. The
+ alternative dependency templates are used only if a symbol
+ line contains the <var>id-of-dependency-template</var>
+ field. The first alternative dependency template is
+ numbered 1, the second 2, and so forth.<footnote>
+ An example of where this may be needed is with a library
+ that implements the libGL interface. All GL
+ implementations provide the same set of base interfaces,
+ and then may provide some additional interfaces only used
+ by programs that require that specific GL implementation.
+ So, for example, libgl1-mesa-glx may use the
+ following <file>symbols</file> file:
+ <example>
+ libGL.so.1 libgl1
+ | libgl1-mesa-glx #MINVER#
+ publicGlSymbol@Base 6.3-1
+ [...]
+ implementationSpecificSymbol@Base 6.5.2-7 1
+ [...]
+ </example>
+ Binaries or shared libraries using
+ only <tt>publicGlSymbol</tt> would depend only
+ on <tt>libgl1</tt> (which may be provided by multiple
+ packages), but ones
+ using <tt>implementationSpecificSymbol</tt> would get a
+ dependency on <tt>libgl1-mesa-glx (>= 6.5.2-7)</tt>
+ </footnote>
+ </p>
+
+ <p>
+ Finally, the entry for the library may contain one or more
+ metadata fields. Currently, the only
+ supported <var>field-name</var>
+ is <tt>Build-Depends-Package</tt>, whose value lists
+ the <qref id="sharedlibs-dev">library development
+ package</qref> on which packages using this shared library
+ declare a build dependency. If this field is
+ present, <prgn>dpkg-shlibdeps</prgn> uses it to ensure that
+ the resulting binary package dependency on the shared
+ library is at least as strict as the source package
+ dependency on the shared library development
+ package.<footnote>
+ This field should normally not be necessary, since if the
+ behavior of any symbol has changed, the corresponding
+ symbol <var>minimal-version</var> should have been
+ increased. But including it makes the <tt>symbols</tt>
+ system more robust by tightening the dependency in cases
+ where the package using the shared library specifically
+ requires at least a particular version of the shared
+ library development package for some reason.
+ </footnote>
+ For our example, the <tt>zlib1g</tt> <file>symbols</file>
+ file would contain:
+ <example compact="compact">
+ * Build-Depends-Package: zlib1g-dev
+ </example>
+ </p>
+
+ <p>
+ Also see <manref name="deb-symbols" section="5">.
+ </p>
+ </sect2>
+
+ <sect2 id="providing-symbols">
+ <heading>Providing a <file>symbols</file> file</heading>
+
+ <p>
+ If your package provides a shared library, you should
+ arrange to include a <file>symbols</file> control file
+ following the format described above in that package. You
+ must include either a <file>symbols</file> control file or
+ a <file>shlibs</file> control file.
+ </p>
+
+ <p>
+ Normally, this is done by creating a <file>symbols</file> in
+ the source package
+ named <file>debian/<var>package</var>.symbols</file>
+ or <file>debian/symbols</file>, possibly
+ with <file>.<var>arch</var></file> appended if the symbols
+ information varies by architecture. This file may use the
+ extended syntax documented in <manref name="dpkg-gensymbols"
+ section="1">. Then, call <prgn>dpkg-gensymbols</prgn> as
+ part of the package build process. It will
+ create <file>symbols</file> files in the package staging
+ area based on the binaries and libraries in the package
+ staging area and the <file>symbols</file> files in the
+ source package.<footnote>
+ If you are
+ using <tt>debhelper</tt>, <prgn>dh_makeshlibs</prgn> will
+ take care of calling either <prgn>dpkg-gensymbols</prgn>
+ or generating a <file>shlibs</file> file as appropriate.
+ </footnote>
+ </p>
+
+ <p>
+ Packages that provide <file>symbols</file> files must keep
+ them up-to-date to ensure correct dependencies in packages
+ that use the shared libraries. This means updating
+ the <file>symbols</file> file whenever a new public symbol
+ is added, changing the <var>minimal-version</var> field
+ whenever a symbol changes behavior or signature in a
+ backward-compatible way (see <ref id="sharedlibs-updates">),
+ and changing the <var>library-soname</var>
+ and <var>main-dependency-template</var>, and probably all of
+ the <var>minimal-version</var> fields, when the library
+ changes <tt>SONAME</tt>. Removing a public symbol from
+ the <file>symbols</file> file because it's no longer
+ provided by the library normally requires changing
+ the <tt>SONAME</tt> of the library.
+ See <ref id="sharedlibs-runtime"> for more information
+ on <tt>SONAME</tt>s.
+ </p>
+ </sect2>
+ </sect1>
+
+ <sect1 id="sharedlibs-shlibdeps">
+ <heading>The <tt>shlibs</tt> system</heading>
+
+ <p>
+ The <tt>shlibs</tt> system is an simpler alternative to
+ the <tt>symbols</tt> system for declaring dependencies for
+ shared libraries. It may be more appropriate for C++
+ libraries and other cases where tracking individual symbols is
+ too difficult. It predated the <tt>symbols</tt> system and is
+ therefore frequently seen in older packages. It is also
+ required for udebs, which do not support <tt>symbols</tt>.
+ </p>
- </p>
- </footnote>
- </p>

- <p>
- In the following sections, we will first describe where the
- various <tt>shlibs</tt> files are to be found, then how to
- use <prgn>dpkg-shlibdeps</prgn>, and finally the <tt>shlibs</tt>
- file format and how to create them if your package contains a
- shared library.
- </p>
+ <p>
+ In the following sections, we will first describe where the
+ various <file>shlibs</file> files are to be found, then how to
+ use <prgn>dpkg-shlibdeps</prgn>, and finally
+ the <file>shlibs</file> file format and how to create them.
+ </p>

- <sect1>
- <heading>The <tt>shlibs</tt> files present on the system</heading>
+ <sect2 id="shlibs-paths">
+ <heading>The <file>shlibs</file> files present on the
+ system</heading>

- <p>
- There are several places where <tt>shlibs</tt> files are
- found. The following list gives them in the order in which
- they are read by
- <qref id="pkg-dpkg-shlibdeps"><prgn>dpkg-shlibdeps</prgn></qref>.
- (The first one which gives the required information is used.)
- </p>
-
- <p>
- <list>
+ <p>
+ There are several places where <tt>shlibs</tt> files are
+ found. The following list gives them in the order in which
+ they are read by <prgn>dpkg-shlibdeps</prgn>. (The first
+ one which gives the required information is used.)
+ <list>
- <item>
- <p><file>debian/shlibs.local</file></p>
+ <item>
+ <p><file>debian/shlibs.local</file></p>

- <p>
- This lists overrides for this package. This file should
- normally not be used, but may be needed temporarily in
- unusual situations to work around bugs in other packages,
- or in unusual cases where the normally declared dependency
- information in the installed <file>shlibs</file> file for
- a library cannot be used. This file overrides information
- obtained from any other source.
- </p>
- </item>
+ <p>
+ This lists overrides for this package. This file
+ should normally not be used, but may be needed
+ temporarily in unusual situations to work around bugs
+ in other packages, or in unusual cases where the
+ normally declared dependency information in the
+ installed <file>shlibs</file> file for a library
+ cannot be used. This file overrides information
+ obtained from any other source.
+ </p>
+ </item>

- <item>
- <p><file>/etc/dpkg/shlibs.override</file></p>
+ <item>
+ <p><file>/etc/dpkg/shlibs.override</file></p>

- <p>
- This lists global overrides. This list is normally
- empty. It is maintained by the local system
- administrator.
- </p>
- </item>
+ <p>
+ This lists global overrides. This list is normally
+ empty. It is maintained by the local system
+ administrator.
+ </p>
+ </item>

- <item>
- <p><file>DEBIAN/shlibs</file> files in the "build directory"</p>
+ <item>
+ <p><file>DEBIAN/shlibs</file> files in the "build
+ directory"</p>

- <p>
- When packages are being built,
- any <file>debian/shlibs</file> files are copied into the
- control information file area of the temporary build
- directory and given the name <file>shlibs</file>. These
- files give details of any shared libraries included in the
- same package.<footnote>
- An example may help here. Let us say that the source
- package <tt>foo</tt> generates two binary
- packages, <tt>libfoo2</tt> and <tt>foo-runtime</tt>.
- When building the binary packages, the two packages are
- created in the directories <file>debian/libfoo2</file>
- and <file>debian/foo-runtime</file> respectively.
- (<file>debian/tmp</file> could be used instead of one of
- these.) Since <tt>libfoo2</tt> provides the
- <tt>libfoo</tt> shared library, it will require a
- <tt>shlibs</tt> file, which will be installed in
- <file>debian/libfoo2/DEBIAN/shlibs</file>, eventually to
- become <file>/var/lib/dpkg/info/libfoo2.shlibs</file>.
- When <prgn>dpkg-shlibdeps</prgn> is run on the
- executable <file>debian/foo-runtime/usr/bin/foo-prog</file>,
- it will examine
- the <file>debian/libfoo2/DEBIAN/shlibs</file> file to
- determine whether <tt>foo-prog</tt>'s library
- dependencies are satisfied by any of the libraries
- provided by <tt>libfoo2</tt>. For this reason,
- <prgn>dpkg-shlibdeps</prgn> must only be run once all of
- the individual binary packages' <tt>shlibs</tt> files
- have been installed into the build directory.
- </footnote>
- </p>
- </item>
+ <p>
+ These files are generated as part of the package build
+ process and staged for inclusion as control files in
+ the binary packages being built. They provide details
+ of any shared libraries included in the same package.
+ </p>
+ </item>

- <item>
- <p><file>/var/lib/dpkg/info/*.shlibs</file></p>
+ <item>
+ <p><file>shlibs</file> control files for packages
+ installed on the system</p>

- <p>
- These are the <file>shlibs</file> files corresponding to
- all of the packages installed on the system, and are
- maintained by the relevant package maintainers.
- </p>
- </item>
+ <p>
+ The <file>shlibs</file> control files for all the
+ packages currently installed on the system. These are
+ normally found
+ in <file>/var/lib/dpkg/info/*.symbols</file>, but
+ packages should not rely on this and instead should
+ use <tt>dpkg-query --control-path <var>package</var>
+ shlibs</tt> if for some reason these files need to be
+ examined.
+ </p>
+ </item>

- <item>
- <p><file>/etc/dpkg/shlibs.default</file></p>
+ <item>
+ <p><file>/etc/dpkg/shlibs.default</file></p>

- <p>
- This file lists any shared libraries whose packages
- have failed to provide correct <file>shlibs</file> files.
- It was used when the <file>shlibs</file> setup was first
- introduced, but it is now normally empty. It is
- maintained by the <tt>dpkg</tt> maintainer.
- </p>
- </item>
- </list>
- </p>
- </sect1>
+ <p>
+ This file lists any shared libraries whose packages
+ have failed to provide correct <file>shlibs</file>
+ files. It was used when the <file>shlibs</file> setup
+ was first introduced, but it is now normally empty.
+ It is maintained by the <tt>dpkg</tt> maintainer.
+ </p>
+ </item>
+ </list>
+ </p>
+
+ <p>
+ If a <file>symbols</file> file for a shared library package
+ is available, <prgn>dpkg-shlibdeps</prgn> will always use it
+ in preference to a <file>shlibs</file>, with the exception
+ of <file>debian/shlibs.local</file>. The latter overrides
+ any other <file>shlibs</file> or <file>symbols</file> files.
+ </p>
+ </sect2>
-
- <sect1>
- <heading>How to use <prgn>dpkg-shlibdeps</prgn> and the
- <file>shlibs</file> files</heading>
-
- <p>
- Put a call to
- <qref id="pkg-dpkg-shlibdeps"><prgn>dpkg-shlibdeps</prgn></qref>
- into your <file>debian/rules</file> file. If your package
- contains only compiled binaries and libraries (but no scripts),
- you can use a command such as:
- <example compact="compact">
-dpkg-shlibdeps debian/tmp/usr/bin/* debian/tmp/usr/sbin/*
- debian/tmp/usr/lib/*
- </example>
- Otherwise, you will need to explicitly list the compiled
- binaries and libraries.<footnote>
- If you are using <tt>debhelper</tt>, the
- <prgn>dh_shlibdeps</prgn> program will do this work for you.
- It will also correctly handle multi-binary packages.
- </footnote>
- </p>
-
- <p>
- This command puts the dependency information into the
- <file>debian/substvars</file> file, which is then used by
- <prgn>dpkg-gencontrol</prgn>. You will need to place a
- <tt>${shlibs:Depends}</tt> variable in the <tt>Depends</tt>
- field in the control file for this to work.
- </p>
-
- <p>
- If you have multiple binary packages, you will need to call
- <prgn>dpkg-shlibdeps</prgn> on each one which contains
- compiled libraries or binaries. In such a case, you will
- need to use the <tt>-T</tt> option to the <tt>dpkg</tt>
- utilities to specify a different <file>substvars</file> file.
- </p>
-
- <p>
- If you are creating a udeb for use in the Debian Installer,
- you will need to specify that <prgn>dpkg-shlibdeps</prgn>
- should use the dependency line of type <tt>udeb</tt> by
- adding the <tt>-tudeb</tt> option<footnote>
- <prgn>dh_shlibdeps</prgn> from the <tt>debhelper</tt> suite
- will automatically add this option if it knows it is
- processing a udeb.
- </footnote>. If there is no dependency line of
- type <tt>udeb</tt> in the <file>shlibs</file>
- file, <prgn>dpkg-shlibdeps</prgn> will fall back to the regular
- dependency line.
- </p>
-
- <p>
- For more details on <prgn>dpkg-shlibdeps</prgn>, please see
- <ref id="pkg-dpkg-shlibdeps"> and
- <manref name="dpkg-shlibdeps" section="1">.
- </p>
- </sect1>

- <sect1 id="shlibs">
- <heading>The <file>shlibs</file> File Format</heading>
+ <sect2 id="shlibs">
+ <heading>The <file>shlibs</file> File Format</heading>

- <p>
- Each <file>shlibs</file> file has the same format. Lines
- beginning with <tt>#</tt> are considered to be comments and
- are ignored. Each line is of the form:
- <example compact="compact">
-[<var>type</var>: ]<var>library-name</var> <var>soname-version</var> <var>dependencies ...</var>
- </example>
- </p>
+ <p>
+ Each <file>shlibs</file> file has the same format. Lines
+ beginning with <tt>#</tt> are considered to be comments and
+ are ignored. Each line is of the form:
+ <example compact="compact">
+ [<var>type</var>: ]<var>library-name</var> <var>soname-version</var> <var>dependencies ...</var>
+ </example>
+ </p>

- <p>
- We will explain this by reference to the example of the
- <tt>zlib1g</tt> package, which (at the time of writing)
- installs the shared library <file>/usr/lib/libz.so.1.1.3</file>.
- </p>
+ <p>
+ We will explain this by reference to the example of the
+ <tt>zlib1g</tt> package, which (at the time of writing)
+ installs the shared
+ library <file>/usr/lib/libz.so.1.2.3.4</file>.
+ </p>

- <p>
- <var>type</var> is an optional element that indicates the type
- of package for which the line is valid. The only type currently
- in use is <tt>udeb</tt>. The colon and space after the type are
- required.
- </p>
+ <p>
+ <var>type</var> is an optional element that indicates the
+ type of package for which the line is valid. The only type
+ currently in use is <tt>udeb</tt>. The colon and space
+ after the type are required.
+ </p>

- <p>
- <var>library-name</var> is the name of the shared library,
- in this case <tt>libz</tt>. (This must match the name part
- of the soname, see below.)
- </p>
+ <p>
+ <var>library-name</var> is the name of the shared library,
+ in this case <tt>libz</tt>. (This must match the name part
+ of the soname, see below.)
+ </p>

+ <p>
+ <var>soname-version</var> is the version part of the
+ ELF <tt>SONAME</tt> attribute of the library, determined the
+ same way that the <var>soversion</var> component of the
+ recommended shared library package name is determined.
+ See <ref id="sharedlibs-runtime"> for the details.
+ </p>
- <p>
- <var>soname-version</var> is the version part of the soname of
- the library. The soname is the thing that must exactly match
- for the library to be recognized by the dynamic linker, and is
- usually of the form
- <tt><var>name</var>.so.<var>major-version</var></tt>, in our
- example, <tt>libz.so.1</tt>.<footnote>
- This can be determined using the command
- <example compact="compact">
-objdump -p /usr/lib/libz.so.1.1.3 | grep SONAME
- </example>
- </footnote>
- The version part is the part which comes after
- <tt>.so.</tt>, so in our case, it is <tt>1</tt>. The soname may
- instead be of the form
- <tt><var>name</var>-<var>major-version</var>.so</tt>, such
- as <tt>libdb-4.8.so</tt>, in which case the name would
- be <tt>libdb</tt> and the version would be <tt>4.8</tt>.
- </p>

+ <p>
+ <var>dependencies</var> has the same syntax as a dependency
+ field in a binary package control file. It should give
+ details of which packages are required to satisfy a binary
+ built against the version of the library contained in the
+ package. See <ref id="depsyntax"> for details on the
+ syntax, and <ref id="sharedlibs-updates"> for details on how
+ to maintain the dependency version constraint.
+ </p>
- <p>
- <var>dependencies</var> has the same syntax as a dependency
- field in a binary package control file. It should give
- details of which packages are required to satisfy a binary
- built against the version of the library contained in the
- package. See <ref id="depsyntax"> for details.
- </p>

+ <p>
+ In our example, if the last change to the <tt>zlib1g</tt>
+ package that could change behavior for a client of that
+ library was in version <tt>1:1.2.3.3.dfsg-1</tt>, then
+ the <tt>shlibs</tt> entry for this library could say:
+ <example compact="compact">
+ libz 1 zlib1g (>= 1:1.2.3.3.dfsg-1)
+ </example>
+ This version restriction must be new enough that any binary
+ built against the current version of the library will work
+ with any version of the shared library that satisfies that
+ dependency.
+ </p>
- <p>
- In our example, if the first version of the <tt>zlib1g</tt>
- package which contained a minor number of at least
- <tt>1.3</tt> was <var>1:1.1.3-1</var>, then the
- <tt>shlibs</tt> entry for this library could say:
- <example compact="compact">
-libz 1 zlib1g (>= 1:1.1.3)
- </example>
- The version-specific dependency is to avoid warnings from
- the dynamic linker about using older shared libraries with
- newer binaries.
- </p>

+ <p>
+ As zlib1g also provides a udeb containing the shared
+ library, there would also be a second line:
+ <example compact="compact">
+ udeb: libz 1 zlib1g-udeb (>= 1:1.2.3.3.dfsg-1)
+ </example>
+ </p>
+ </sect2>
- <p>
- As zlib1g also provides a udeb containing the shared library,
- there would also be a second line:
- <example compact="compact">
-udeb: libz 1 zlib1g-udeb (>= 1:1.1.3)
- </example>
- </p>
- </sect1>

- <sect1>
- <heading>Providing a <file>shlibs</file> file</heading>
+ <sect2>
+ <heading>Providing a <file>shlibs</file> file</heading>

- <p>
- If your package provides a shared library, you need to create
- a <file>shlibs</file> file following the format described above.
- It is usual to call this file <file>debian/shlibs</file> (but if
- you have multiple binary packages, you might want to call it
- <file>debian/shlibs.<var>package</var></file> instead). Then
- let <file>debian/rules</file> install it in the control
- information file area:
- <example compact="compact">
-install -m644 debian/shlibs debian/tmp/DEBIAN
- </example>
- or, in the case of a multi-binary package:
- <example compact="compact">
-install -m644 debian/shlibs.<var>package</var> debian/<var>package</var>/DEBIAN/shlibs
- </example>
- An alternative way of doing this is to create the
- <file>shlibs</file> file in the control information file area
- directly from <file>debian/rules</file> without using
- a <file>debian/shlibs</file> file at all,<footnote>
- This is what <prgn>dh_makeshlibs</prgn> in
- the <package>debhelper</package> suite does. If your package
- also has a udeb that provides a shared
- library, <prgn>dh_makeshlibs</prgn> can automatically generate
- the <tt>udeb:</tt> lines if you specify the name of the udeb
- with the <tt>--add-udeb</tt> option.
- </footnote>
- since the <file>debian/shlibs</file> file itself is ignored by
- <prgn>dpkg-shlibdeps</prgn>.
- </p>
+ <p>
+ To provide a <file>shlibs</file> file for a shared library
+ binary package, create a <file>shlibs</file> file following
+ the format described above and place it in
+ the <file>DEBIAN</file> directory for that package during
+ the build. It will then be included as a control file for
+ that package<footnote>
+ This is what <prgn>dh_makeshlibs</prgn> in
+ the <package>debhelper</package> suite does. If your
+ package also has a udeb that provides a shared
+ library, <prgn>dh_makeshlibs</prgn> can automatically
+ generate the <tt>udeb:</tt> lines if you specify the name
+ of the udeb with the <tt>--add-udeb</tt> option.
+ </footnote>.
+ </p>

+ <p>
+ Since <prgn>dpkg-shlibdeps</prgn> reads
+ the <file>DEBIAN/shlibs</file> files in all of the binary
+ packages being built from this source package, all of
+ the <file>DEBIAN/shlibs</file> files should be installed
+ before <prgn>dpkg-shlibdeps</prgn> is called on any of the
+ binary packages.
+ </p>
+ </sect2>
+ </sect1>
- <p>
- As <prgn>dpkg-shlibdeps</prgn> reads the
- <file>DEBIAN/shlibs</file> files in all of the binary packages
- being built from this source package, all of the
- <file>DEBIAN/shlibs</file> files should be installed before
- <prgn>dpkg-shlibdeps</prgn> is called on any of the binary
- packages.
- </p>
- </sect1>
</sect>
</chapt>

@@ -7760,8 +8281,9 @@ INSTALL = install -s # (or use strip on the files in debian/tmp)
Although not enforced by the build tools, shared libraries
must be linked against all libraries that they use symbols from
in the same way that binaries are. This ensures the correct
- functioning of the <qref id="sharedlibs-shlibdeps">shlibs</qref>
- system and guarantees that all libraries can be safely opened
+ functioning of the <qref id="sharedlibs-symbols">symbols</qref>
+ and <qref id="sharedlibs-shlibdeps">shlibs</qref>
+ systems and guarantees that all libraries can be safely opened
with <tt>dlopen()</tt>. Packagers may wish to use the gcc
option <tt>-Wl,-z,defs</tt> when building a shared library.
Since this option enforces symbol resolution at build time,
@@ -10573,82 +11095,10 @@ END-INFO-DIR-ENTRY
</heading>

<p>
- This program is usually called from <file>debian/rules</file>
- just before <prgn>dpkg-gencontrol</prgn> (see <ref
- id="pkg-sourcetree">), in the top level of the source tree.
- </p>
-
- <p>
- Its arguments are executables and shared libraries
- <footnote>
- <p>
- They may be specified either in the locations in the
- source tree where they are created or in the locations
- in the temporary build tree where they are installed
- prior to binary package creation.
- </p>
- </footnote> for which shared library dependencies should
- be included in the binary package's control file.
- </p>
-
- <p>
- If some of the found shared libraries should only
- warrant a <tt>Recommends</tt> or <tt>Suggests</tt>, or if
- some warrant a <tt>Pre-Depends</tt>, this can be achieved
- by using the <tt>-d<var>dependency-field</var></tt> option
- before those executable(s). (Each <tt>-d</tt> option
- takes effect until the next <tt>-d</tt>.)
- </p>
-
- <p>
- <prgn>dpkg-shlibdeps</prgn> does not directly cause the
- output control file to be modified. Instead by default it
- adds to the <file>debian/substvars</file> file variable
- settings like <tt>shlibs:Depends</tt>. These variable
- settings must be referenced in dependency fields in the
- appropriate per-binary-package sections of the source
- control file.
- </p>
-
- <p>
- For example, a package that generates an essential part
- which requires dependencies, and optional parts that
- which only require a recommendation, would separate those
- two sets of dependencies into two different fields.<footnote>
- At the time of writing, an example for this was the
- <package/xmms/ package, with Depends used for the xmms
- executable, Recommends for the plug-ins and Suggests for
- even more optional features provided by unzip.
- </footnote>
- It can say in its <file>debian/rules</file>:
- <example>
- dpkg-shlibdeps -dDepends <var>program anotherprogram ...</var>
- -dRecommends <var>optionalpart anotheroptionalpart</var>
- </example>
- and then in its main control file <file>debian/control</file>:
- <example>
- <var>...</var>
- Depends: ${shlibs:Depends}
- Recommends: ${shlibs:Recommends}
- <var>...</var>
- </example>
- </p>
-
- <p>
- Sources which produce several binary packages with
- different shared library dependency requirements can use
- the <tt>-p<var>varnameprefix</var></tt> option to override
- the default <tt>shlibs:</tt> prefix (one invocation of
- <prgn>dpkg-shlibdeps</prgn> per setting of this option).
- They can thus produce several sets of dependency
- variables, each of the form
- <tt><var>varnameprefix</var>:<var>dependencyfield</var></tt>,
- which can be referred to in the appropriate parts of the
- binary package control files.
+ See <manref name="dpkg-shlibdeps" section="1">.
</p>
</sect1>

-
<sect1 id="pkg-dpkg-distaddfile">
<heading>
<prgn>dpkg-distaddfile</prgn> - adds a file to

Jonathan Nieder 07-09-2012 03:51 AM

document symbols
 
Jonathan Nieder wrote:

> I'll reply with an interdiff relative to the last version of the
> patch.

Here it is.
Subject: Clarifications to symbols and shlibs policy

subject/verb agreement: s/provide/provides/

Packages with libraries or binaries linking to a shared library must
use symbols or shlibs files to compute their dependencies. Packages
that dlopen() a shared library should do so as well, but since that
is not typical practice and the tools to do that don't exist, it is
not made a policy "must" yet.

The minimal version for a symbol can be bumped after the version of
the package in which the symbol was introduced.

Add a footnote explaining why shlibs files cannot be used for
libraries with unusual sonames.

The shlibs file for a library udeb goes in the corresponding deb.

The library deb corresponding to a udeb is supposed to provide a
shlibs file, rather than consuming (using) one.

Add "for example" when talking about dpkg-shlibdeps -T. This is
just an illustration and not meant to be normative.

If a library is used both directly and indirectly, the direct
dependency still needs to be declared.

Backward-compatibility is defined in terms of what reasonable
programs and libraries need.

In the normal case, symbols files go in dpkg's admindir as package
control files.

wording fix: "dependency on" avoids some of the ambiguity in
"dependency of".
---
policy.sgml | 86 +++++++++++++++++++++++++++++++++--------------------------
1 file changed, 48 insertions(+), 38 deletions(-)

diff --git a/policy.sgml b/policy.sgml
index 1eb039f8..50ae756c 100644
--- a/policy.sgml
+++ b/policy.sgml
@@ -5838,25 +5838,30 @@ Replaces: mail-transport-agent
whether new library interfaces are available and can be called).
To allow these dependencies to be constructed, shared libraries
must provide either a <file>symbols</file> file or
- a <file>shlibs</file> file, which provide information on the
- package dependencies required to ensure the presence of this
- library. Any package which uses a shared library must use these
- files to determine the required dependencies when it is built.
+ a <file>shlibs</file> file, which provides information on the
+ package dependencies required to ensure the presence of
+ interfaces provided by this library. Any package with binaries
+ or libraries linking to a shared library must use these files
+ to determine the required dependencies when it is built. Other
+ packages which use a shared library (for example using
+ <tt>dlopen()</tt>) should compute appropriate dependencies
+ using these files at build time as well.
</p>

<p>
- These two mechanisms differ in the degree of detail that they
- provide. A <file>symbols</file> file documents every symbol
- that is part of the library ABI and, for each, the version of
- the package in which it was introduced. This permits detailed
- analysis of the symbols used by a particular package and
- construction of an accurate dependency, but it requires the
- package maintainer to track more information about the shared
- library. A <file>shlibs</file> file, in contrast, only
- documents the last time the library ABI changed in any way. It
- only provides information about the library as a whole, not
- individual symbols. When a package is built using a shared
- library with only a <file>shlibs</file> file, the generated
+ The two mechanisms differ in the degree of detail that they
+ provide. A <file>symbols</file> file documents for each symbol
+ exported by a library the minimal version of the package any
+ binary using this symbol will need, which is typically the
+ version of the package in which the symbol was introduced.
+ This permits detailed analysis of the symbols used by a
+ particular package and construction of an accurate dependency,
+ but it requires the package maintainer to track more information
+ about the shared library. A <file>shlibs</file> file, in
+ contrast, only documents the last time the library ABI changed
+ in any way. It only provides information about the library as a
+ whole, not individual symbols. When a package is built using a
+ shared library with only a <file>shlibs</file> file, the generated
dependency will require a version of the shared library equal to
or newer than the version of the last ABI change. This
generates unnecessarily restrictive dependencies compared
@@ -5869,7 +5874,11 @@ Replaces: mail-transport-agent
<p>
<file>shlibs<file> files also have a flawed representation of
library SONAMEs, making it difficult to use <file>shlibs</file>
- files in some unusual corner cases.
+ files in some unusual corner cases.<footnote>
+ libfooN.shlibs says 'libfoo N' instead of the actual SONAME,
+ so if the SONAME doesn't match one of the two expected
+ formats (libfoo-N.so or libfoo.so.N) it can't be represented.
+ </footnote>
</p>

<p>
@@ -5879,9 +5888,9 @@ Replaces: mail-transport-agent
required by <file>symbols</file> files is not too difficult to
maintain. However, maintaining exhaustive symbols information
for a C++ library can be quite onerous, so <file>shlibs</file>
- files may be more appropriate for most C++ libraries. udebs
- must also use <file>shlibs</file>, since the udeb infrastructure
- does not use <file>symbols</file>.
+ files may be more appropriate for most C++ libraries. Libraries
+ with a corresponding udeb must also provide <file>shlibs</file>,
+ since the udeb infrastructure does not use <file>symbols</file>.
</p>

<sect1 id="dpkg-shlibdeps">
@@ -5940,8 +5949,8 @@ Replaces: mail-transport-agent
binaries, libraries, or loadable modules. If you have
multiple binary packages, you will need to
call <prgn>dpkg-shlibdeps</prgn> on each one which contains
- compiled libraries or binaries, using the <tt>-T</tt> option
- to the <tt>dpkg</tt> utilities to specify a
+ compiled libraries or binaries, for example using the
+ <tt>-T</tt> option to the <tt>dpkg</tt> utilities to specify a
different <file>substvars</file> file for each binary
package.<footnote>
Again, <prgn>dh_shlibdeps</prgn>
@@ -5969,8 +5978,8 @@ Replaces: mail-transport-agent
linked <em>indirectly</em> to <tt>foo</tt>, and the dynamic
linker will load them automatically when it
loads <tt>libbar</tt>. A package should depend on the
- libraries it directly uses, but not the libraries it
- indirectly uses. The dependencies for the libraries used
+ libraries it directly uses, but not the libraries it only uses
+ indirectly. The dependencies for the libraries used
directly will automatically pull in the indirectly-used
libraries. <prgn>dpkg-shlibdeps</prgn> will handle this logic
automatically, but package maintainers need to be aware of
@@ -6014,14 +6023,15 @@ Replaces: mail-transport-agent
<p>
There are two types of ABI changes: ones that are
backward-compatible and ones that are not. An ABI change is
- backward-compatible if any binary was linked with the previous
- version of the shared library will still work correctly with
- the new version of the shared library. Adding new symbols to
- the shared library is a backward-compatible change. Removing
- symbols from the shared library is not. Changing the behavior
- of a symbol may or may not be backward-compatible depending on
- the change; for example, changing a function to accept a new
- enum constant not previously used by the library is generally
+ backward-compatible if any reasonable program or library that
+ was linked with the previous version of the shared library
+ will still work correctly with the new version of the shared
+ library. Adding new symbols to the shared library is a
+ backward-compatible change. Removing symbols from the shared
+ library is not. Changing the behavior of a symbol may or may
+ not be backward-compatible depending on the change; for
+ example, changing a function to accept a new enum constant not
+ previously used by the library is generally
backward-compatible, but changing the members of a struct that
is passed into library functions is generally not unless the
library takes special precautions to accept old versions of
@@ -6122,10 +6132,10 @@ Replaces: mail-transport-agent

<p>
<file>symbols</file> files for a shared library are normally
- provided by the shared library package, but there are
- several override paths that are checked first in case that
- information is wrong or missing. The following list gives
- them in the order in which they are read
+ provided by the shared library package as a control file,
+ but there are several override paths that are checked first
+ in case that information is wrong or missing. The following
+ list gives them in the order in which they are read
by <prgn>dpkg-shlibdeps</prgn> The first one that contains
the required information is used.
<list>
@@ -6342,9 +6352,9 @@ Replaces: mail-transport-agent
compressBound@ZLIB_1.2.0 1:1.2.0
</example>
Packages using only <tt>compress</tt> would then get a
- dependency of <tt>zlib1g (>= 1:1.1.4)</tt>, but packages
+ dependency on <tt>zlib1g (>= 1:1.1.4)</tt>, but packages
using <tt>compressBound</tt> would get a dependency
- of <tt>zlib1g (>= 1:1.2.0)</tt>.
+ on <tt>zlib1g (>= 1:1.2.0)</tt>.
</p>

<p>
--
1.7.10.4

Russ Allbery 08-12-2012 09:10 PM

document symbols
 
Jonathan Nieder <jrnieder@gmail.com> writes:
> Russ Allbery wrote:

>> I'm therefore including here the complete SGML source of that section
>> not in diff format, followed by the diff of everything *outside* of
>> that section. I think this will be easier to review.

> Thanks! I would have preferred a diff since it shows the text that is
> being replaced, too, but let's go with this for a first pass.

Yeah, it's frustrating to review something this large, and none of the
normal tools do a particularly good job at it. A side-by-side contextual
diff tool is probably best.

Anyway, thank you for the detailed review, and apologies for taking so
long to get back to this. The amount of work required is intimidating,
and I kept putting it off.

For the most part, I adopted your changes; assume that if I don't comment
here specifically, I've incorporated that change. (I started by applying
your interdiff and then only changing the bits that I thought I could
further clarify.)

> [...]
>> <p>
>> If a package contains a binary or library which links to a
>> shared library, we must ensure that, when the package is
>> installed on the system, all of the libraries needed are also
>> installed.

> This text is carried over from before and contains a requirement I never
> noticed before. Suppose my package contains two binaries: maintool and
> side-tool. The latter is not very important and links to libbiglibrary.
> I might be tempted to make the dependency by my package on libbiglibrary
> a Recommends instead of a Depends. The above says I must not.

> Intentional? It seems like good policy, anyway.

Could you open a separate bug about this? I think we should allow
Recommends, but as you say it's already in the current wording and this
change is already too complicated. We should discuss it separately.

> This means packages must not hard-code library dependencies. It also
> seems like good policy, but I suspect it would render packages such as
> chromium that use dlopen() and hard-code the corresponding library name
> in dependencies RC-buggy.

Your fix (making dependencies for dlopen a should instead of a must)
looked like a good way of fixing this problem to me. Thanks!

>> To allow these dependencies to be constructed, shared libraries
>> must provide either a <file>symbols</file> file or
>> a <file>shlibs</file> file, which provide information on the
>> package dependencies required to ensure the presence of this
>> library.

> Subject/verb agreement: s/provide/provides/

While that's technically correct, it looks completely wrong to me. I
reworded to make this two sentences instead, so that it's both formally
correct and "feels" right.

> If I remove a symbol that was documented to be private or change the
> behavior of a function when given invalid arguments, is that a
> backward-compatible change?

> If I add change the implementation in such a way that the library
> becomes so large that some large programs cannot use it any more, is
> that a backward-incompatible change?

You addressed this by introducing the concept of a "reasonable" program
but not defining it. That sounded like the right approach to me, but I
felt the need to say more, so I added a footnote explaining the intent:

There are two types of ABI changes: ones that are
backward-compatible and ones that are not. An ABI change is
backward-compatible if any reasonable program or library that
was linked with the previous version of the shared library
will still work correctly with the new version of the shared
library.<footnote>
An example of an "unreasonable" program is one that uses library
interfaces that are documented as internal and unsupported. If the
only programs or libraries affected by a change are "unreasonable"
ones, other techniques, such as declaring <tt>Breaks</tt>
relationships with affected packages or treating their usage of the
library as bugs in those packages, may be appropriate instead of
changing the SONAME. However, the default approach is to change the
SONAME for any change to the ABI that could break a program.
</footnote>

> Unrelated change. The patch would have been easier to review if this
> were a separate commit, which could have gone straight to master since
> it doesn't change the output.

Yes, sorry. I really hate the whole diff system for making changes to
text documents, since I always reformat text documents as I work on them.
I'll try to avoid this when people find it confusing, but as long as I'm
writing the patches, you may have to just live with some of this, since
putting more barriers in the way of writing text for Policy will mean that
I'll do even less work than I do now. :/ That said, I agree that it's
kind of annoying for review, and I'll try to get better about not doing
it.

--
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Jonathan Nieder 08-12-2012 11:15 PM

document symbols
 
Russ Allbery wrote:

> Okay, once more for the win.

Hoorah! :) I don't see any problems in the normative content, so I'd
second this if I could. Cosmetic nits (patch below):

[...]
> +++ b/policy.sgml
[...]
> @@ -5633,17 +5634,29 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)
[...]
> <p>
> + To determine the <var>soversion</var>, look at
> + the <tt>SONAME</tt> of the library, stored in the
> + ELF <tt>SONAME</tt> attribute. it is usually of the
^^

Capitalization: s/it/It/

[...]
> + A common example of when a change to the is required is a
^^^^^^^^^

Missing word: s/to the/to the dependency version/. (In a previous
version of the patch, this passage was discussing symbols files only
and said <var>minimal-version</var>.)

[...]
> + no symbol version. <var>minimal-version</var> is the most
> + recent version of the shared library that changed the
> + behavior of that symbol, whether by adding it, changing its
~~~~~~ ~~~~~~~~
> + function signature (the parameters, their types, or the
> + return type), or its behavior in a way that is visible to a
~~~~~~~~~~~~~~~
> + caller. <var>id-of-dependency-template</var> is an optional

Maintaining parallel construction: s/its behavior/changing its
behavior/.

[...]
> + In our example, if the last change to the <tt>zlib1g</tt>
> + package that could change behavior for a client of that
> + library was in version <tt>1:1.2.3.3.dfsg-1</tt>, then
> + the <tt>shlibs</tt> entry for this library could say:
> + <example compact="compact">
> + libz 1 zlib1g (>= 1:1.2.3.3.dfsg-1)
> + </example>

Should this say (>= 1:1.2.3.3.dfsg-1~) or (>= 1:1.2.3.3.dfsg) to be
kind to backporters? Before the patch, the example said ">= 1:1.1.3".

-- >8 --
Subject: symbols/shlibs policy: cosmetic fixes

Use "zlib1g (>= 1:1.2.3.3.dfsg-2~)" in the sample shlibs dependency
field to emphasize the backport-friendly convention described in the
sharedlibs-updates section.

Also correct two small typos --- one sentence is uncapitalized and
another missing a noun --- and rephrase a sentence that describes when
to bump the dependency-version to make it easier to read.
---
diff --git a/policy.sgml b/policy.sgml
index fa1c39a..050c688 100644
--- a/policy.sgml
+++ b/policy.sgml
@@ -5646,7 +5646,7 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)
<p>
To determine the <var>soversion</var>, look at
the <tt>SONAME</tt> of the library, stored in the
- ELF <tt>SONAME</tt> attribute. it is usually of the
+ ELF <tt>SONAME</tt> attribute. It is usually of the
form <tt><var>name</var>.so.<var>major-version</var></tt> (for
example, <tt>libz.so.1</tt>). The version part is the part
which comes after <tt>.so.</tt>, so in that example it
@@ -6238,9 +6238,9 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)
</p>

<p>
- A common example of when a change to the is required is a
- function that takes an enum or struct argument that controls
- what the function does. For example:
+ A common example of when a change to the dependency version
+ is required is a function that takes an enum or struct
+ argument that controls what the function does. For example:
<example>
enum library_op { OP_FOO, OP_BAR };
int library_do_operation(enum library_op);
@@ -6489,8 +6489,9 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)
recent version of the shared library that changed the
behavior of that symbol, whether by adding it, changing its
function signature (the parameters, their types, or the
- return type), or its behavior in a way that is visible to a
- caller. <var>id-of-dependency-template</var> is an optional
+ return type), or changing its behavior in a way that is
+ visible to a caller.
+ <var>id-of-dependency-template</var> is an optional
field that references
an <var>alternative-dependency-template</var>; see below for
a full description.
@@ -6795,10 +6796,10 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)
<p>
In our example, if the last change to the <tt>zlib1g</tt>
package that could change behavior for a client of that
- library was in version <tt>1:1.2.3.3.dfsg-1</tt>, then
+ library was in version <tt>1:1.2.3.3.dfsg-2</tt>, then
the <tt>shlibs</tt> entry for this library could say:
<example compact="compact">
- libz 1 zlib1g (>= 1:1.2.3.3.dfsg-1)
+ libz 1 zlib1g (>= 1:1.2.3.3.dfsg-2~)
</example>
This version restriction must be new enough that any binary
built against the current version of the library will work
@@ -6810,7 +6811,7 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)
As zlib1g also provides a udeb containing the shared
library, there would also be a second line:
<example compact="compact">
- udeb: libz 1 zlib1g-udeb (>= 1:1.2.3.3.dfsg-1)
+ udeb: libz 1 zlib1g-udeb (>= 1:1.2.3.3.dfsg-2~)
</example>
</p>
</sect2>


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Russ Allbery 08-12-2012 11:33 PM

document symbols
 
Jonathan Nieder <jrnieder@gmail.com> writes:

> Hoorah! :) I don't see any problems in the normative content, so I'd
> second this if I could. Cosmetic nits (patch below):

Thanks, applied.

>> + In our example, if the last change to the <tt>zlib1g</tt>
>> + package that could change behavior for a client of that
>> + library was in version <tt>1:1.2.3.3.dfsg-1</tt>, then
>> + the <tt>shlibs</tt> entry for this library could say:
>> + <example compact="compact">
>> + libz 1 zlib1g (>= 1:1.2.3.3.dfsg-1)
>> + </example>

> Should this say (>= 1:1.2.3.3.dfsg-1~) or (>= 1:1.2.3.3.dfsg) to be
> kind to backporters? Before the patch, the example said ">= 1:1.1.3".

Let's go with 1:1.2.3.3.dfsg in the example to show the common case
instead of the unusual case. I've applied this:

commit 29e3fc2e05b59a7e13913a263a1e22d40cbc9918
Author: Russ Allbery <rra@debian.org>
Date: Sun Aug 12 16:32:35 2012 -0700

Reflect the common case in the shlibs example

diff --git a/policy.sgml b/policy.sgml
index 050c688..3c863dc 100644
--- a/policy.sgml
+++ b/policy.sgml
@@ -6796,10 +6796,10 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)
<p>
In our example, if the last change to the <tt>zlib1g</tt>
package that could change behavior for a client of that
- library was in version <tt>1:1.2.3.3.dfsg-2</tt>, then
+ library was in version <tt>1:1.2.3.3.dfsg-1</tt>, then
the <tt>shlibs</tt> entry for this library could say:
<example compact="compact">
- libz 1 zlib1g (>= 1:1.2.3.3.dfsg-2~)
+ libz 1 zlib1g (>= 1:1.2.3.3.dfsg)
</example>
This version restriction must be new enough that any binary
built against the current version of the library will work
@@ -6811,7 +6811,7 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)
As zlib1g also provides a udeb containing the shared
library, there would also be a second line:
<example compact="compact">
- udeb: libz 1 zlib1g-udeb (>= 1:1.2.3.3.dfsg-2~)
+ udeb: libz 1 zlib1g-udeb (>= 1:1.2.3.3.dfsg)
</example>
</p>
</sect2>

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Russ Allbery (rra@debian.org) <http://www.eyrie.org/~eagle/>


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Jonathan Nieder 08-12-2012 11:38 PM

document symbols
 
Russ Allbery wrote:

> Let's go with 1:1.2.3.3.dfsg in the example to show the common case
> instead of the unusual case. I've applied this:

Thanks. Looks good.


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