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random: fix crash on some 64bit platforms 

rbx needs to be stashed in a 64bit register on 64bit platforms. With this crash
in particular, it was holding a stack canary which was not properly restored
after the cpuid.

Split out the x86+PIC case so that x86_64 doesn't have to worry about it.
This commit is contained in:
Cory Fields 2017-06-16 14:43:35 -04:00
parent c2ab38bdd5
commit 9af207c810
1 changed files with 8 additions and 2 deletions
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10
src/random.cpp
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@ -72,10 +72,16 @@ static bool rdrand_supported = false;
static constexpr uint32_t CPUID_F1_ECX_RDRAND = 0x40000000;
static void RDRandInit()
{
//! When calling cpuid function #1, ecx register will have this set if RDRAND is available.
uint32_t eax, ecx, edx;
#if defined(__i386__) && ( defined(__PIC__) || defined(__PIE__))
// Avoid clobbering ebx, as that is used for PIC on x86.
uint32_t eax, tmp, ecx, edx;
uint32_t tmp;
__asm__ ("mov %%ebx, %1; cpuid; mov %1, %%ebx": "=a"(eax), "=g"(tmp), "=c"(ecx), "=d"(edx) : "a"(1));
#else
uint32_t ebx;
__asm__ ("cpuid": "=a"(eax), "=b"(ebx), "=c"(ecx), "=d"(edx) : "a"(1));
#endif
//! When calling cpuid function #1, ecx register will have this set if RDRAND is available.
if (ecx & CPUID_F1_ECX_RDRAND) {
LogPrintf("Using RdRand as entropy source\n");
rdrand_supported = true;