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runtime: use a fence instruction before rdtsc

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This implements the same choices made in the gc runtime, except that
    for 32-bit x86 we only use the fence instruction if the processor
    supports SSE2.
    
    The code here is hacked up for speed; the gc runtime uses straight
    assembler.
    
    Reviewed-on: https://go-review.googlesource.com/97715

From-SVN: r258336
This commit is contained in:
Ian Lance Taylor 2018-03-07 14:31:03 +00:00
parent 6cde8c545b
commit 2dab5d909f
2 changed files with 56 additions and 5 deletions
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2
gcc/go/gofrontend/MERGE
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@ -1,4 +1,4 @@
3287064c24cbf0c50776cdb87a720d29130b4363
2a07cd31927ac943104f55d2b696e53e7cd073b3
The first line of this file holds the git revision number of the last
merge done from the gofrontend repository.

59
libgo/runtime/runtime_c.c
View File

@ -33,13 +33,47 @@ runtime_atoi(const byte *p, intgo len)
return n;
}
#if defined(__i386__) || defined(__x86_64__) || defined (__s390__) || defined (__s390x__)
// When cputicks is just asm instructions, skip the split stack
// prologue for speed.
int64 runtime_cputicks(void) __attribute__((no_split_stack));
#endif
// Whether the processor supports SSE2.
#if defined (__i386__)
static _Bool hasSSE2;
// Force appropriate CPU level so that we can call the lfence/mfence
// builtins.
#pragma GCC push_options
#pragma GCC target("sse2")
#elif defined(__x86_64__)
#define hasSSE2 true
#endif
#if defined(__i386__) || defined(__x86_64__)
// Whether to use lfence, as opposed to mfence.
// Set based on cpuid.
static _Bool lfenceBeforeRdtsc;
#endif // defined(__i386__) || defined(__x86_64__)
int64
runtime_cputicks(void)
{
#if defined(__386__) || defined(__x86_64__)
uint32 low, high;
asm("rdtsc" : "=a" (low), "=d" (high));
return (int64)(((uint64)high << 32) | (uint64)low);
#if defined(__i386__) || defined(__x86_64__)
if (hasSSE2) {
if (lfenceBeforeRdtsc) {
__builtin_ia32_lfence();
} else {
__builtin_ia32_mfence();
}
}
return __builtin_ia32_rdtsc();
#elif defined (__s390__) || defined (__s390x__)
uint64 clock = 0;
/* stckf may not write the return variable in case of a clock error, so make
@ -56,6 +90,10 @@ runtime_cputicks(void)
#endif
}
#if defined(__i386__)
#pragma GCC pop_options
#endif
void
runtime_signalstack(byte *p, uintptr n)
{
@ -146,8 +184,21 @@ runtime_cpuinit()
#if defined(__i386__) || defined(__x86_64__)
unsigned int eax, ebx, ecx, edx;
if (__get_cpuid(0, &eax, &ebx, &ecx, &edx)) {
if (eax != 0
&& ebx == 0x756E6547 // "Genu"
&& edx == 0x49656E69 // "ineI"
&& ecx == 0x6C65746E) { // "ntel"
lfenceBeforeRdtsc = true;
}
}
if (__get_cpuid(1, &eax, &ebx, &ecx, &edx)) {
setCpuidECX(ecx);
#if defined(__i386__)
if ((edx & bit_SSE2) != 0) {
hasSSE2 = true;
}
#endif
}
#if defined(HAVE_AS_X86_AES)