[Fwd: Bogus PNI flag in /proc/cpuinfo]

[Dario Birtic]

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> Hello,
>
> I am expiriencing bogus PNI /proc/cpuinfo flag (and as far I can tell,
> out of plenty of auxillary /proc/cpuinfo flags I have seen on the
> internet, everyone having the athlon64 architecture also):
>
> cat /proc/cpuinfo
> processor       : 0
> vendor_id       : AuthenticAMD
> cpu family      : 15
> model           : 15
> model name      : AMD Athlon(tm) 64 Processor 3500+
> stepping        : 0
> cpu MHz         : 2340.189
> cache size      : 512 KB
> fpu             : yes
> fpu_exception   : yes
> cpuid level     : 1
> wp              : yes
> flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
> mca cmov pat pse36 clflush mmx fxsr sse sse2 pni syscall nx mmxext lm
> 3dnowext 3dnow
> bogomips        : 4636.67
> TLB size        : 1024 4K pages
> clflush size    : 64
> cache_alignment : 64
> address sizes   : 40 bits physical, 48 bits virtual
> power management: ts fid vid ttp
>
> Though this processor doesn't support PNI (aka SSE3) it is reported in
> the flags.
>
> cat /proc/version
> Linux version 2.6.11-gentoo-r6 (root@beast) (gcc version 3.4.3 20041125
> (Gentoo Linux 3.4.3-r1, ssp-3.4.3-0, pie-8.7.7)) #2 Mon Apr 25 00:34:25
> CEST 2005
>
> I am expiriencing this behaviour since cca. 2.6.8.1.
>
> A simple testcase shows:
> cat << "EOF" > test_pni.c
> #include <stdint.h>
>
> uint8_t __attribute__((aligned(64))) current[64];
> uint8_t previous[64];
>
> int main()
> {
>    int i;
>    uint64_t result;
>    uint32_t _eax, _ebx, _ecx, _edx;
>    uint8_t _cpuid[13];
>    uint32_t *_cpuid0 = (uint32_t*) _cpuid;
>    uint32_t *_cpuid1 = (uint32_t*) ( _cpuid + 4 );
>    uint32_t *_cpuid2 = (uint32_t*) ( _cpuid + 8 );
>    uint8_t *ptr0 = current;
>    uint8_t *ptr1 = previous;
>
>    __asm__ __volatile__ (
>          "cpuid\n"
>          : "=a" (_eax),
>          "=b" (*_cpuid0), "=d" (*_cpuid1), "=c" (*_cpuid2)
>          : "a" (0) );
>    _cpuid[12] = 0;
>    printf( "cpuid(0) returns %d (%s)\n", _eax, _cpuid );
>    __asm__ __volatile__ (
>          "cpuid\n"
>          : "=a" (_eax), "=b" (_ebx), "=c" (_ecx), "=d" (_edx)
>          : "a" (1) );
>    printf( "cpuid(1) returns %08x %08x %08x %08x\n",
>          _eax, _ebx, _ecx, _edx );
>    memset( current, 0xaa, 64 );
>    memset( previous, 0x55, 64 );
>    for( i = 0; i < 4; i ++ ) {
>       __asm__ __volatile__ (
>             "movdqa %0, %%xmm0\n"
>             "movdqu %1, %%xmm1\n"
>             "psadbw %%xmm1, %%xmm0\n"
>             "paddw  %%xmm0, %%xmm2\n"
>             "haddps %%xmm2, %%xmm2\n"
>             "haddps %%xmm2, %%xmm2\n"
>             : : "m" (*ptr0),
>             "m" (*ptr1) : "xmm0", "xmm1", "xmm2" );
>       ptr0 += 16;
>       ptr1 += 16;
>    }
>    __asm__ __volatile__ (
>          "movq %%xmm2, %0\n"
>          : "=m" (result) );
>    printf( "Result is %llu\n", result );
> }
> EOF
> gcc -o test_pni test_pni.c
> ./test_pni
>
> cpuid(0) returns 1 (AuthenticAMD)
> cpuid(1) returns 00000ff0 00000800 00000000 078bfbff
> Illegal instruction
>
> This is expected since there is no PNI on this processor supported
> (haddps being SSE3 instruction). Please also note that ECX bit 0 (PNI
> support) is clear showing that SSE3 is *not* supported.
>
> Regards
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