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Don't install signal handler when checking cpuid #1

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Merged
merged 1 commit into from
Oct 16, 2018
Merged

Don't install signal handler when checking cpuid #1

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49 changes: 13 additions & 36 deletions cpu.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -61,7 +61,9 @@ extern "C"

bool CpuId(word32 input, word32 output[4])
{
#if defined(CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY)
#if !defined(__x86_64__) && !defined(__i386__)
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If this is the

We can instead use conditional compilation to make
sure that we never execute a cpuid instruction on a non x86-64 CPU.

part, what's with the i386 condition?

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Whoops, I got merge happy. cpuid is supported on x86 processors since 1993. We definitely don't care about processors before 1993, but we might someday have a 32-bit build. Seemed slightly more future proof to just proceed with cpuid on any x86 processor. ¯_(ツ)_/¯

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Thanks!

return false;
#elif defined(CRYPTOPP_MS_STYLE_INLINE_ASSEMBLY)
__try
{
__asm
Expand All @@ -88,44 +90,19 @@ bool CpuId(word32 input, word32 output[4])

return true;
#else
// longjmp and clobber warnings. Volatile is required.
// http://github.com/weidai11/cryptopp/issues/24 and http://stackoverflow.com/q/7721854
volatile bool result = true;

volatile SigHandler oldHandler = signal(SIGILL, SigIllHandlerCPUID);
if (oldHandler == SIG_ERR)
return false;

# ifndef __MINGW32__
volatile sigset_t oldMask;
if (sigprocmask(0, NULL, (sigset_t*)&oldMask))
return false;
# endif

if (setjmp(s_jmpNoCPUID))
result = false;
else
{
asm volatile
(
// save ebx in case -fPIC is being used
// TODO: this might need an early clobber on EDI.
asm volatile
(
// save ebx in case -fPIC is being used
// TODO: this might need an early clobber on EDI.
# if CRYPTOPP_BOOL_X32 || CRYPTOPP_BOOL_X64
"pushq %%rbx; cpuid; mov %%ebx, %%edi; popq %%rbx"
"pushq %%rbx; cpuid; mov %%ebx, %%edi; popq %%rbx"
# else
"push %%ebx; cpuid; mov %%ebx, %%edi; pop %%ebx"
"push %%ebx; cpuid; mov %%ebx, %%edi; pop %%ebx"
# endif
: "=a" (output[0]), "=D" (output[1]), "=c" (output[2]), "=d" (output[3])
: "a" (input), "c" (0)
);
}

# ifndef __MINGW32__
sigprocmask(SIG_SETMASK, (sigset_t*)&oldMask, NULL);
# endif

signal(SIGILL, oldHandler);
return result;
: "=a" (output[0]), "=D" (output[1]), "=c" (output[2]), "=d" (output[3])
: "a" (input), "c" (0)
);
return true;
#endif
}

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