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Old 05-04-2010, 10:23 PM
Thomas Bächler
 
Default gcc 4.5 breakage

I noticed problem with gcc 4.5 and the GAP system
(http://www.gap-system.org) first: It throws a few aliasing warnings,
and the program breaks. When I used -fno-strict-aliasing, the warnings
disappeared, but the breakage remained, unless I used -O0. Fixing the
aliasing problems also fixed the breakage.

Now I noticed the exact same issue with busybox:
- Building with -Os throws lots of aliasing warnings, busybox's sed breaks
- Building with -Os -fno-strict-aliasing builds without warnings, but it
still breaks.
- Building with -O0 works, but it isn't optimal.

This will affect LOTS of other programs and these errors will not show
up as errors or warnings during the build procedure.
 
Old 05-05-2010, 12:46 AM
Allan McRae
 
Default gcc 4.5 breakage

On 05/05/10 08:23, Thomas Bächler wrote:

I noticed problem with gcc 4.5 and the GAP system
(http://www.gap-system.org) first: It throws a few aliasing warnings,
and the program breaks. When I used -fno-strict-aliasing, the warnings
disappeared, but the breakage remained, unless I used -O0. Fixing the
aliasing problems also fixed the breakage.

Now I noticed the exact same issue with busybox:
- Building with -Os throws lots of aliasing warnings, busybox's sed breaks
- Building with -Os -fno-strict-aliasing builds without warnings, but it
still breaks.
- Building with -O0 works, but it isn't optimal.


Interesting... Does fixing the aliasing fix this one too? I see no
upstream bug reports that seem related so you should follow it up there.
I will pull in a new gcc-4.5 snapshot next week when I do the
glibc-2.12 toolchain rebuild so hopefully that may contain a fix that I
am missing...



This will affect LOTS of other programs and these errors will not show
up as errors or warnings during the build procedure.


As an aside 15% of the packages in the repos have been updated since gcc
made it to [core]. From the lack of bug reports, the breakage does not
appear too widespread
 
Old 05-05-2010, 07:26 AM
Thomas Bächler
 
Default gcc 4.5 breakage

Am 05.05.2010 02:46, schrieb Allan McRae:
>> Now I noticed the exact same issue with busybox:
>> - Building with -Os throws lots of aliasing warnings, busybox's sed
>> breaks
>> - Building with -Os -fno-strict-aliasing builds without warnings, but it
>> still breaks.
>> - Building with -O0 works, but it isn't optimal.
>
> Interesting... Does fixing the aliasing fix this one too? I see no
> upstream bug reports that seem related so you should follow it up there.
> I will pull in a new gcc-4.5 snapshot next week when I do the
> glibc-2.12 toolchain rebuild so hopefully that may contain a fix that I
> am missing...

I can only guess. You can remove -fno-strict-aliasing from the
mkinitcpio-busybox PKGBUILD and build, then count the number of warnings
- there's hundreds.

I opened an upstream bug report, but I was so far unable to produce a
test case they can use.
 
Old 05-06-2010, 07:44 AM
Thomas Bächler
 
Default gcc 4.5 breakage

Am 05.05.2010 02:46, schrieb Allan McRae:
> Interesting... Does fixing the aliasing fix this one too? I see no
> upstream bug reports that seem related so you should follow it up there.
> I will pull in a new gcc-4.5 snapshot next week when I do the
> glibc-2.12 toolchain rebuild so hopefully that may contain a fix that I
> am missing...

There is no fix in the latest 4.5 branch (or trunk) yet.
http://gcc.gnu.org/PR43987 has more details.

Basically, the problem is caused by -ftree-fta, which is on by default
with -O1 and higher (and also -Os, which I use for busybox). The bug can
be worked around with -fno-tree-fta until a fix becomes available.
 
Old 05-06-2010, 07:45 AM
Thomas Bächler
 
Default gcc 4.5 breakage

Am 06.05.2010 09:44, schrieb Thomas Bächler:
> Am 05.05.2010 02:46, schrieb Allan McRae:
>> Interesting... Does fixing the aliasing fix this one too? I see no
>> upstream bug reports that seem related so you should follow it up there.
>> I will pull in a new gcc-4.5 snapshot next week when I do the
>> glibc-2.12 toolchain rebuild so hopefully that may contain a fix that I
>> am missing...
>
> There is no fix in the latest 4.5 branch (or trunk) yet.
> http://gcc.gnu.org/PR43987 has more details.
>
> Basically, the problem is caused by -ftree-fta, which is on by default
> with -O1 and higher (and also -Os, which I use for busybox). The bug can
> be worked around with -fno-tree-fta until a fix becomes available.
>

Writing is difficult - it's -free-pta and -fno-tree-pta, of course.
 
Old 05-06-2010, 11:33 AM
Allan McRae
 
Default gcc 4.5 breakage

On 06/05/10 17:45, Thomas Bächler wrote:

Am 06.05.2010 09:44, schrieb Thomas Bächler:

Am 05.05.2010 02:46, schrieb Allan McRae:

Interesting... Does fixing the aliasing fix this one too? I see no
upstream bug reports that seem related so you should follow it up there.
I will pull in a new gcc-4.5 snapshot next week when I do the
glibc-2.12 toolchain rebuild so hopefully that may contain a fix that I
am missing...


There is no fix in the latest 4.5 branch (or trunk) yet.
http://gcc.gnu.org/PR43987 has more details.

Basically, the problem is caused by -ftree-fta, which is on by default
with -O1 and higher (and also -Os, which I use for busybox). The bug can
be worked around with -fno-tree-fta until a fix becomes available.



Writing is difficult - it's -free-pta and -fno-tree-pta, of course.



Don't worry... the gcc guy who fixed the bug got it wrong too!

There is a patch on gcc trunk now:
http://gcc.gnu.org/viewcvs/trunk/gcc/tree-ssa-structalias.c?r1=159098&r2=159097&pathrev=159098

I expect glibc-2.12 to be released in the next few days, so I will hold
off until the next gcc-4.5 snapshot is released in the hope that this
fix gets backported by then. If not, it looks a simple backport, so I
will adjust the patch.


Allan
 
Old 05-06-2010, 01:25 PM
RogutÄ—s Sparnuotos
 
Default gcc 4.5 breakage

Thomas Bächler (2010-05-06 09:45):
> Am 06.05.2010 09:44, schrieb Thomas Bächler:
> > Am 05.05.2010 02:46, schrieb Allan McRae:
> >> Interesting... Does fixing the aliasing fix this one too? I see no
> >> upstream bug reports that seem related so you should follow it up there.
> >> I will pull in a new gcc-4.5 snapshot next week when I do the
> >> glibc-2.12 toolchain rebuild so hopefully that may contain a fix that I
> >> am missing...
> >
> > There is no fix in the latest 4.5 branch (or trunk) yet.
> > http://gcc.gnu.org/PR43987 has more details.
> >
> > Basically, the problem is caused by -ftree-fta, which is on by default
> > with -O1 and higher (and also -Os, which I use for busybox). The bug can
> > be worked around with -fno-tree-fta until a fix becomes available.
> >
>
> Writing is difficult - it's -free-pta and -fno-tree-pta, of course.

I wasted a lot of time yesterday:

1. Compiled the kernel from git (for radeon stuff), rebooted.
2. 'ninit' segfaulted, 'ls' from busybox segfaulted.
3. Read your mail about busybox breakage, upgraded busybox with
-fno-tree-pta, but... the same segfaults with kernels compiled by
gcc-4.5.
4. Played with the kernel config for hours until finding out that
CONFIG_CC_OPTIMIZE_FOR_SIZE=y causes the segfaults (and only on
x86_64).

I wonder whether this is something more specific to my setup, or nobody
is compiling kernels with CONFIG_CC_OPTIMIZE_FOR_SIZE=y on x86_64 with
gcc-4.5 (building with gcc-4.4 works)...

All this is probably unrelated to http://gcc.gnu.org/PR43987, but perhaps
it will save some time for someone, as your post about busybox helped me.
I'll wait for a new gcc package before reporting a gcc bug.

--
-- RogutÄ—s Sparnuotos

P.S.
The only good thing about the wasted time was that I found out how to use
qemu for testing: $ qemu-system-x86_64 -kernel bzImage -initrd initrd.img
 
Old 05-06-2010, 02:54 PM
Thomas Bächler
 
Default gcc 4.5 breakage

Am 06.05.2010 15:25, schrieb RogutÄ—s Sparnuotos:
> I wasted a lot of time yesterday:
>
> 1. Compiled the kernel from git (for radeon stuff), rebooted.
> 2. 'ninit' segfaulted, 'ls' from busybox segfaulted.
> 3. Read your mail about busybox breakage, upgraded busybox with
> -fno-tree-pta, but... the same segfaults with kernels compiled by
> gcc-4.5.

The busybox in the repositories is still built with gcc 4.4 - otherwise
nobody would be able to boot. I'll be building a new version soon
though, which is why I discovered this problem in the first place.

> 4. Played with the kernel config for hours until finding out that
> CONFIG_CC_OPTIMIZE_FOR_SIZE=y causes the segfaults (and only on
> x86_64).
>
> I wonder whether this is something more specific to my setup, or nobody
> is compiling kernels with CONFIG_CC_OPTIMIZE_FOR_SIZE=y on x86_64 with
> gcc-4.5 (building with gcc-4.4 works)...

At least in Arch, we don't use that option for our kernels. It is pretty
bad that this breaks.
 
Old 05-06-2010, 03:52 PM
Xavier Chantry
 
Default gcc 4.5 breakage

On Thu, May 6, 2010 at 3:25 PM, RogutÄ—s Sparnuotos
<rogutes@googlemail.com> wrote:
>
> All this is probably unrelated to http://gcc.gnu.org/PR43987, but perhaps
> it will save some time for someone, as your post about busybox helped me.
> I'll wait for a new gcc package before reporting a gcc bug.
>

IMO you should report it now, especially considering that the current
package is a stable gcc release.

Thu May 6 18:30:01 2010
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Hello!

There is an open source firmware:

http://linuxtv.org/hg/~anttip/af9015

Could this be included in debian to make the usb dvb tuner work?

thanks

&nbsp;<a href="http://ad.adverticum.net/b/cl,1,73468,1594255,1591992/click.prm" target="_blank">__________________________________ ______________________<br>Reform�s: 0066<br>211 int��, 4 120 munkat�, 184 000 tal�oz�<br></a>



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Archive: http://lists.debian.org/freemail.20100506172622.29359.3@xmldata15.freemail .hu
 
Old 05-10-2010, 10:45 AM
Thomas Bächler
 
Default gcc 4.5 breakage

Am 05.05.2010 00:23, schrieb Thomas Bächler:
> I noticed problem with gcc 4.5 and the GAP system
> (http://www.gap-system.org) first: It throws a few aliasing warnings,
> and the program breaks. When I used -fno-strict-aliasing, the warnings
> disappeared, but the breakage remained, unless I used -O0. Fixing the
> aliasing problems also fixed the breakage.
>
> Now I noticed the exact same issue with busybox:
> - Building with -Os throws lots of aliasing warnings, busybox's sed breaks
> - Building with -Os -fno-strict-aliasing builds without warnings, but it
> still breaks.
> - Building with -O0 works, but it isn't optimal.
>
> This will affect LOTS of other programs and these errors will not show
> up as errors or warnings during the build procedure.
>

I am now building busybox with -O0 again, as '-Os -fno-strict-aliasing
-fno-tree-pta' seemed to work at first, but it turned out the 'sed'
output from busybox was just a few unreadable characters. I tested -O0
and it fixes the problems, but the binary is way too large.

Btw, why do I always get signoffs, then move it, and only then get these
reports?
 

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