On (Wed) Feb 18 2009 [08:49:33], Avi Kivity wrote:
> Amit Shah wrote:
>> On (Wed) Feb 18 2009 [13:21:26], Amit Shah wrote:
>>
>>> On (Tue) Feb 17 2009 [12:47:10], Brian Kress wrote:
>>>
>>>> When I try to run KVM built off the current head, it crashes with a
>>>> Segmentation fault. KVM-84 does
>>>> not. Seems to be dealing with the CPUID changes:
>>>>
>>>>
>>>> 0x081a5c70 in host_cpuid ()
>>>> at /home/kressb/kvm/src/qemu/target-i386/helper.c:1426
>>>> 1426 asm volatile("pusha \n\t"
>>>>
>>> This looks like some kind of stack corruption on 32-bit:
>>>
>>> 1472 if (kvm_enabled())
>>> (gdb)
>>> 1473 host_cpuid(0, 0, NULL, ebx, ecx, edx);
>>> (gdb)
>>>
>>> Program received signal SIGSEGV, Segmentation fault.
>>> 0x081a2d60 in host_cpuid (function=10, count=1231384169, eax=0x0,
>>> ebx=0xadfc1914,
>>> ecx=0xadfc1910, edx=0xadfc190c)
>>> at /home/amit/src/kvm-userspace/qemu/target-i386/helper.c:1426
>>> 1426 asm volatile("pusha \n\t"
>>>
>>> I don't see this on 64-bit. Investigating.
>>>
>>
>> Avi, what's the reason for doing this in the host_cpuid code? As I see
>> it, the first version should work for both 64-bit and 32-bit code.
>>
>> #ifdef __x86_64__
>> asm volatile("cpuid"
>> : "=a"(vec[0]), "=b"(vec[1]),
>> "=c"(vec[2]), "=d"(vec[3])
>> : "0"(function), "c"(count) : "cc");
>> #else
>> asm volatile("pusha \n\t"
>> "cpuid \n\t"
>> "mov %%eax, 0(%1) \n\t"
>> "mov %%ebx, 4(%1) \n\t"
>> "mov %%ecx, 8(%1) \n\t"
>> "mov %%edx, 12(%1) \n\t"
>> "popa"
>> : : "a"(function), "c"(count), "S"(vec)
>> : "memory", "cc");
>> #endif
>>
>
> The first version generates too much register pressure for some
> compilers on i386, leading to compilation failures. The second version
Is it still valid? I tried with gcc-4.1.2 and that worked fine with the
first version. Should we just use that version instead?
> is surely wrong, though? Counting from zero, the "vec" parameter would
> be %2, not %1.
Looks like I missed out updating that when I introduced 'count'. Fixing
that fixes the problem.
Amit
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