[arch-general] [arch-dev-public] [toolchain] gcc 4.5 breakage

Rogutės Sparnuotos rogutes at googlemail.com
Thu May 6 15:25:28 CEST 2010

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
4. Played with the kernel config for hours until finding out that
   CONFIG_CC_OPTIMIZE_FOR_SIZE=y causes the segfaults (and only on

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.

--  Rogutės Sparnuotos

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

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