* [Bug c/56068] -march=native creates Illegal instruction on KVM guests
2013-01-21 17:08 [Bug c/56068] New: -march=native creates Illegal instruction on KVM guests jpyeron at pdinc dot us
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--- Comment #1 from Jason Pyeron <jpyeron at pdinc dot us> 2013-01-21 17:08:47 UTC ---
Created attachment 29239
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29239
gcc -dM -E - -march=native
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--- Comment #2 from Jason Pyeron <jpyeron at pdinc dot us> 2013-01-21 17:10:34 UTC ---
Created attachment 29240
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29240
diff of defines
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--- Comment #3 from Jason Pyeron <jpyeron at pdinc dot us> 2013-01-21 17:12:15 UTC ---
mockbuild@centos6-64bit-builder ~/build/BUILD/tmp (mock-chroot)
$ cat /proc/cpuinfo
processor : 0
vendor_id : AuthenticAMD
cpu family : 6
model : 13
model name : QEMU Virtual CPU version (cpu64-rhel6)
stepping : 3
cpu MHz : 2194.498
cache size : 512 KB
fpu : yes
fpu_exception : yes
cpuid level : 4
wp : yes
flags : fpu de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat
pse36 clflush mmx fxsr sse sse2 syscall nx lm up unfair_spinlock pni cx16
hypervisor lahf_lm abm sse4a
bogomips : 4388.99
TLB size : 1024 4K pages
clflush size : 64
cache_alignment : 64
address sizes : 48 bits physical, 48 bits virtual
power management:
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--- Comment #4 from Jason Pyeron <jpyeron at pdinc dot us> 2013-01-21 17:13:25 UTC ---
Created attachment 29241
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29241
gcc -v test.c output
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--- Comment #5 from Jason Pyeron <jpyeron at pdinc dot us> 2013-01-21 17:14:05 UTC ---
Created attachment 29242
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29242
gcc test.c -march=native -v
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--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-01-21 17:14:54 UTC ---
> sse4a
There is the issue I think.
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To: gcc-bugs
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Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target| |x86_64-*-*
Status|UNCONFIRMED |WAITING
Last reconfirmed| |2013-01-21
Component|c |target
Ever Confirmed|0 |1
--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-01-21 17:19:29 UTC ---
Please try a newer version of GCC, 4.4 is no longer supported. Also since this
is 4.4 is going to be modified by RedHat, please report it to them instead. I
don't think bdver2 support was in the official 4.4 release.
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--- Comment #8 from Jason Pyeron <jpyeron at pdinc dot us> 2013-01-21 17:26:06 UTC ---
(In reply to comment #7)
> Please try a newer version of GCC, 4.4 is no longer supported. Also since which version is the oldest supported version, I will use that version for testing.
I will also open a vendor issue. to support the RH GCC 4.4.
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--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-21 17:30:38 UTC ---
What is the illegal instruction? What version of glibc are you using?
I debugged a very similar problem last week where GCC was generating vmovsd on
a host without AVX support. /proc/cpuinfo showed no avx flag, but glibc's
__cpuid reported the AVX bit set which makes GCC use -mavx. This is a glibc
bug, it should not set the AVX bit if the OSXSAVE bit is not also set. This
seems to predominantly affect VMs, but in my case was not a VM. The glibc bug
is fixed in 2.15, see http://sourceware.org/bugzilla/show_bug.cgi?id=14059 and
http://sourceware.org/bugzilla/show_bug.cgi?id=13753
Using -mno-avx (or replacing -march=cirei7) worked for me.
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--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-21 17:32:52 UTC ---
(In reply to comment #9)
> Using -mno-avx (or replacing -march=cirei7) worked for me.
Bah, that should be "replacing -march=native with -march=corei7"
My problem was with GCC 4.6, and the avx-detection code is the same in current
releases, so if your illegal instruction is an AVX one then I doubt trying a
newer GCC will help. The problem is in glibc's __cpuid() function not GCC.
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--- Comment #11 from Jason Pyeron <jpyeron at pdinc dot us> 2013-01-21 17:42:06 UTC ---
(In reply to comment #10)
> (In reply to comment #9)
> > Using -mno-avx (or replacing -march=cirei7) worked for me.
> Bah, that should be "replacing -march=native with -march=corei7"
> My problem was with GCC 4.6, and the avx-detection code is the same in current
> releases, so if your illegal instruction is an AVX one then I doubt trying a
> newer GCC will help. The problem is in glibc's __cpuid() function not GCC.
I will try 4.6 to prove that. Off to build 4.6...
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--- Comment #12 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-21 19:14:14 UTC ---
(In reply to comment #11)
> I will try 4.6 to prove that. Off to build 4.6...
Thanks for checking. See http://gcc.gnu.org/wiki/InstallingGCC for the
foolproof way to do build it.
You could also try this with any GCC version on the KVM guest:
#include <stdio.h>
#include "cpuid.h"
int main()
{
unsigned bit_osxsave = bit_AVX >> 1;
unsigned int eax, ebx, ecx, edx;
__cpuid (1, eax, ebx, ecx, edx);
printf("bit_OSXSAVE (%u) = %u\n", bit_osxsave, ecx & bit_osxsave);
printf("bit_AVX (%u) = %u\n", bit_AVX, ecx & bit_AVX);
}
If that prints 0 for OSXSAVE and non-zero for AVX then it's the same problem I
had.
Maybe GCC could work around it by checking both flags in the AVX detection
logic.
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--- Comment #13 from Uros Bizjak <ubizjak at gmail dot com> 2013-01-21 19:31:47 UTC ---
(In reply to comment #12)
> (In reply to comment #11)
> > I will try 4.6 to prove that. Off to build 4.6...
>
> Thanks for checking. See http://gcc.gnu.org/wiki/InstallingGCC for the
> foolproof way to do build it.
>
> You could also try this with any GCC version on the KVM guest:
>
> #include <stdio.h>
> #include "cpuid.h"
>
> int main()
> {
> unsigned bit_osxsave = bit_AVX >> 1;
>
> unsigned int eax, ebx, ecx, edx;
>
> __cpuid (1, eax, ebx, ecx, edx);
>
> printf("bit_OSXSAVE (%u) = %u\n", bit_osxsave, ecx & bit_osxsave);
> printf("bit_AVX (%u) = %u\n", bit_AVX, ecx & bit_AVX);
> }
>
> If that prints 0 for OSXSAVE and non-zero for AVX then it's the same problem I
> had.
>
> Maybe GCC could work around it by checking both flags in the AVX detection
> logic.
Recent 4.6+ does. Please see driver-i386.c around line 470:
--snip--
/* Get XCR_XFEATURE_ENABLED_MASK register with xgetbv. */
#define XCR_XFEATURE_ENABLED_MASK 0x0
#define XSTATE_FP 0x1
#define XSTATE_SSE 0x2
#define XSTATE_YMM 0x4
if (has_osxsave)
asm (".byte 0x0f; .byte 0x01; .byte 0xd0"
: "=a" (eax), "=d" (edx)
: "c" (XCR_XFEATURE_ENABLED_MASK));
/* Check if SSE and YMM states are supported. */
if (!has_osxsave
|| (eax & (XSTATE_SSE | XSTATE_YMM)) != (XSTATE_SSE | XSTATE_YMM))
{
has_avx = 0;
has_fma = 0;
has_fma4 = 0;
has_xop = 0;
}
--snip--
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From: redi at gcc dot gnu.org @ 2013-01-21 19:59 UTC (permalink / raw)
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--- Comment #14 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-01-21 19:58:48 UTC ---
(In reply to comment #13)
> > Maybe GCC could work around it by checking both flags in the AVX detection
> > logic.
>
> Recent 4.6+ does. Please see driver-i386.c around line 470:
Ah, thank you! I only looked in the 4.6.3 and 4.7.2 releases, not the branch
heads.
That's good to know.
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--- Comment #15 from Jason Pyeron <jpyeron at pdinc dot us> 2013-01-21 20:14:10 UTC ---
(In reply to comment #12)
> (In reply to comment #11)
> > I will try 4.6 to prove that. Off to build 4.6...
> ...
> If that prints 0 for OSXSAVE and non-zero for AVX then it's the same problem I
> had.
> Maybe GCC could work around it by checking both flags in the AVX detection
> logic.
mockbuild@centos6-64bit-builder ~/build/BUILD/gcc/test (mock-chroot)
$ gcc test.c -march=native
mockbuild@centos6-64bit-builder ~/build/BUILD/gcc/test (mock-chroot)
$ ./a.out
bit_OSXSAVE (134217728) = 0
bit_AVX (268435456) = 0
mockbuild@centos6-64bit-builder ~/build/BUILD/gcc/test (mock-chroot)
$ gcc test.c
mockbuild@centos6-64bit-builder ~/build/BUILD/gcc/test (mock-chroot)
$ ./a.out
bit_OSXSAVE (134217728) = 0
bit_AVX (268435456) = 0
on the other note, I am currently building
svn://gcc.gnu.org/svn/gcc/branches/gcc-4_6-branch
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From: rguenth at gcc dot gnu.org @ 2013-01-23 16:42 UTC (permalink / raw)
To: gcc-bugs
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Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|WAITING |RESOLVED
Resolution| |INVALID
--- Comment #16 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-23 16:42:19 UTC ---
mockbuild@centos6-64bit-builder ~/build/BUILD/tmp (mock-chroot)
$ cat /proc/cpuinfo
processor : 0
vendor_id : AuthenticAMD
cpu family : 6
model : 13
I think that's the old qemu bug of providing a non-sensical CPUID
family/model/vendor combination by default on x86_64. AMD family 6
is 32bits only. Intel family 6 has 64bit support.
You'll hit funny issues with GMP as well. Thus, fix your KVM/QEMU
config.
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