I want to do a profiling in my software using TSC, running under Linux
x86_64. I tried to search on my local disk
for a example and found out in SQLite3:
#elif (defined(__GNUC__) && defined(__x86_64__))
__inline__ sqlite_uint64 sqlite3Hwtime(void){
unsigned long val;
__asm__ __volatile__ ("rdtsc" : "=A" (val));
return val;
}
I ported it into my software, but the result val is 32-bit. I've
download the newest version of sqlite3, but it's the same.
Then I tried to figure out using of TSC in Linux kernel:
/*
* both i386 and x86_64 returns 64-bit value in edx:eax, but gcc's "A"
* constraint has different meanings. For i386, "A" means exactly
* edx:eax, while for x86_64 it doesn't mean rdx:rax or edx:eax. Instead,
* it means rax *or* rdx.
*/
#ifdef CONFIG_X86_64
#define DECLARE_ARGS(val, low, high) unsigned low, high
#define EAX_EDX_VAL(val, low, high) ((low) | ((u64)(high) << 32))
#define EAX_EDX_ARGS(val, low, high) "a" (low), "d" (high)
#define EAX_EDX_RET(val, low, high) "=a" (low), "=d" (high)
#else
#define DECLARE_ARGS(val, low, high) unsigned long long val
#define EAX_EDX_VAL(val, low, high) (val)
#define EAX_EDX_ARGS(val, low, high) "A" (val)
#define EAX_EDX_RET(val, low, high) "=A" (val)
#endif
..............................................
static __always_inline unsigned long long __native_read_tsc(void)
{
DECLARE_ARGS(val, low, high);
asm volatile("rdtsc" : EAX_EDX_RET(val, low, high));
return EAX_EDX_VAL(val, low, high);
}
Does sqlite3 intend to use 32-bit time stamp on x86_64, or this is a bug?
--
Cyberman Wu
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