Bug#432861: Compiles arch/x86_64/kernel/signal.c from Linux 2.6.22 incorrectly

[Martin Orr <martin@martinorr.name>]

Package: gcc-4.2
Version: 4.2-20070707-1
Severity: important

When I build the kernel (either 2.6.21 or 2.6.22) with gcc 4.2-20070707-1,
then try to boot, I get a hang in udevsettle.  If I build with gcc
4.2-20070627-1, everything is fine.

The file which matters is arch/x86_64/kernel/signal.c.  The gcc version used
to compile this file determines whether the bug triggers or not, independent
of the version used to compile the rest of the kernel.

The command used to compile this file is:
gcc -Wp,-MD,arch/x86_64/kernel/.signal.s.d  -nostdinc -isystem
/usr/lib/gcc/x86_64-linux-gnu/4.2.1/include -D__KERNEL__ -Iinclude  -include
include/linux/autoconf.h -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs
-fno-strict-aliasing -fno-common -Os  -march=k8 -m64 -mno-red-zone
-mcmodel=kernel -pipe -Wno-sign-compare -fno-asynchronous-unwind-tables
-funit-at-a-time -mno-sse -mno-mmx -mno-sse2 -mno-3dnow
-maccumulate-outgoing-args   -fstack-protector -fomit-frame-pointer
-fno-stack-protector -Wdeclaration-after-statement -Wno-pointer-sign
-D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(signal)"
-D"KBUILD_MODNAME=KBUILD_STR(signal)" -fverbose-asm -S -o
arch/x86_64/kernel/signal.s arch/x86_64/kernel/signal.c

Note that I am using -Os but replacing this with -O2 still causes the bug.
-O1 and -O0 appear to work correctly.

The assembly which 4.2-20070707 with -Os produces for this file includes the
following clearly silly code:
        orl     %ecx, %esi      # __pu_err, __pu_err
        orl     %edx, %esi      # __pu_err, __pu_err
        orl     %ecx, %esi      # __pu_err, __pu_err
        orl     %eax, %esi      # __pu_err, __pu_err
        orl     %ecx, %esi      # __pu_err, __pu_err
        orl     %ecx, %esi      # __pu_err, __pu_err
        orl     %ecx, %esi      # __pu_err, __pu_err
This is only the error handling, and appears to be something of a red
herring, because -O1 gives a similar silly piece of code but the kernel
still works.

The assembly files produced by different compiler versions and optimisations
are at http://www.srcf.ucam.org/~mpo25/2007/linux-signal/

For more, see http://thread.gmane.org/gmane.linux.kernel/551982/focus=553590

--- System information. ---
Architecture: amd64
Kernel:       Linux 2.6.21

Debian Release: lenny/sid
  990 unstable        www.debian-multimedia.org
  990 unstable        ftp.ie.debian.org
  990 unstable        ftp-uxsup.csx.cam.ac.uk
  500 testing         ftp.ie.debian.org
  500 testing         ftp-uxsup.csx.cam.ac.uk
    1 experimental    ftp.ie.debian.org
    1 experimental    ftp-uxsup.csx.cam.ac.uk

--- Package information. ---
Depends                      (Version) | Installed
======================================-+-======================
gcc-4.2-base        (= 4.2-20070707-1) | 4.2-20070707-1
cpp-4.2             (= 4.2-20070707-1) | 4.2-20070707-1
binutils          (>= 2.17cvs20070426) | 2.17.20070406cvs-2
libgcc1          (>= 1:4.2-20070707-1) | 1:4.2-20070707-1
libgomp1           (>= 4.2-20070707-1) | 4.2-20070707-1
libc6                       (>= 2.5-5) | 2.6-2


-- 
Martin Orr