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Old 07-01-2011, 07:39 AM
Josselin Mouette
 
Default Multiarch and D-Bus

Le lundi 27 juin 2011 * 11:54 +0100, Steve Langasek a écrit :
> It is with excitement and trepidation that I write to you today about the
> status of multiarch support in Debian.

A big thank you to all of those who finally made this possible.

Before we start to work on some packages, I’d like to ask if someone has
checked whether D-Bus is multiarch-safe. Said otherwise, is it possible
to use a D-Bus interface over another architecture? From my limited
D-Bus knowledge I think it should be safe, but if there are some caveats
it’s better to know right now.

Obvious candidates for multiarchification are atk/at-spi2 for a11y,
gio/gvfs for remote filesystem access and gsettings/dconf for
application settings. Each of them will probably require a split between
Multiarch:same and Multiarch:foreign components.

The same question holds for CORBA, but if we can get rid of at-spi and
have GConf ported to D-Bus before the wheezy release, I’m not sure it’s
worth an investigation.

--
.'`. Josselin Mouette
: :' :
`. `'
`-
 
Old 07-01-2011, 08:01 AM
Simon McVittie
 
Default Multiarch and D-Bus

On Fri, 01 Jul 2011 at 09:39:54 +0200, Josselin Mouette wrote:
> Before we start to work on some packages, I’d like to ask if someone has
> checked whether D-Bus is multiarch-safe. Said otherwise, is it possible
> to use a D-Bus interface over another architecture?

D-Bus is machine-word-size-neutral (all types have a known size in bits) so
that's fine. Foreign-endian messages are always *meant* to have worked, but
nobody tested that, so it was broken until recently (CVE-2011-2200). Fixed
now, though.

If a particular D-Bus API bypasses the D-Bus type system and sends
native-endian or native-word-size structs as a byte array, then nothing
in D-Bus will save you from that, but that would be a silly thing
to do, and I'm not aware of any API that does so.

(Coincidentally, I've just uploaded a Multi-Arch: same version of libdbus
to unstable.)

Regards,
S


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Old 07-01-2011, 08:06 AM
Bastien ROUCARIES
 
Default Multiarch and D-Bus

On Fri, Jul 1, 2011 at 10:01 AM, Simon McVittie <smcv@debian.org> wrote:
> On Fri, 01 Jul 2011 at 09:39:54 +0200, Josselin Mouette wrote:
>> Before we start to work on some packages, I’d like to ask if someone has
>> checked whether D-Bus is multiarch-safe. Said otherwise, is it possible
>> to use a D-Bus interface over another architecture?
>
> D-Bus is machine-word-size-neutral (all types have a known size in bits) so
> that's fine. Foreign-endian messages are always *meant* to have worked, but
> nobody tested that, so it was broken until recently (CVE-2011-2200). Fixed
> now, though.
>
> If a particular D-Bus API bypasses the D-Bus type system and sends
> native-endian or native-word-size structs as a byte array, then nothing
> in D-Bus will save you from that, but that would be a silly thing
> to do, and I'm not aware of any API that does so.

Even dark corner like double endianess ?

Bastien

>
> (Coincidentally, I've just uploaded a Multi-Arch: same version of libdbus
> to unstable.)
>
> Regards,
> * *S
>
>
> --
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> Archive: http://lists.debian.org/20110701080104.GB10846@reptile.pseudorandom.co.uk
>
>


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Old 07-01-2011, 08:13 AM
Simon McVittie
 
Default Multiarch and D-Bus

On Fri, 01 Jul 2011 at 09:01:04 +0100, Simon McVittie wrote:
> Foreign-endian messages are always *meant* to have worked

To clarify that a bit: messages can have either endianness, but libdbus
will deal with that transparently, and always give library users data in
native endianness (byteswapping the DBusMessage on-demand if necessary).
If you find a case where this doesn't work, please open a bug, but
I'm reasonably sure it's already right.

S


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Old 07-01-2011, 08:23 AM
Simon McVittie
 
Default Multiarch and D-Bus

On Fri, 01 Jul 2011 at 10:06:34 +0200, Bastien ROUCARIES wrote:
> Even dark corner like double endianess ?

Doubles are byteswapped in exactly the same way as int64, I hope that's
correct everywhere? (dbus/dbus-marshal-byteswap.c around line 73.)

To be more specific: D-Bus assumes that doubles are IEEE-754, in the same
byte order as integers - so all LE architectures have the same double format
as an i386, and all BE architectures have the same double format
as a powerpc. Do we have any architectures where this isn't true?

If we do, then D-Bus over TCP was already non-interoperable on those
architectures; and I've seen similar assumptions in other packages, so
if such architectures exist, D-Bus won't be the only thing that's wrong.

S


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