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kernel/libroot: use compiler built-in for rdtsc().

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* spares two MOV instructions.
* the warning is fixed upstream:
https://github.com/gcc-mirror/gcc/commit/2bbcec1f882a7c1f40b1d0aaa3811f85983dcdb9
This commit is contained in:
Jérôme Duval
2018-05-22 17:48:02 +02:00
parent 3acaf25e8f
commit fc48586b9b
1 changed files with 9 additions and 11 deletions
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src/system/libroot/os/arch/x86_64/system_time.cpp
+9 -11
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@@ -6,6 +6,13 @@
#include <stdint.h> #include <stdint.h>
// disable a warning for GCC 5.4, fixed upstream.
// will remove the pragmas after a while.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-variable"
#include <x86intrin.h>
#pragma GCC diagnostic pop
static uint64_t cv_factor; static uint64_t cv_factor;
static uint64_t cv_factor_nsec; static uint64_t cv_factor_nsec;
@@ -19,19 +26,10 @@ __x86_setup_system_time(uint64_t cv, uint64_t cv_nsec)
} }
static inline uint64_t
rdtsc()
{
uint64_t lo, hi;
__asm__("rdtsc" : "=a" (lo), "=d" (hi));
return lo | (hi << 32);
}
extern "C" [[gnu::optimize("omit-frame-pointer")]] int64_t extern "C" [[gnu::optimize("omit-frame-pointer")]] int64_t
system_time() system_time()
{ {
__uint128_t time = static_cast<__uint128_t>(rdtsc()) * cv_factor; __uint128_t time = static_cast<__uint128_t>(__rdtsc()) * cv_factor;
return time >> 64; return time >> 64;
} }
@@ -39,7 +37,7 @@ system_time()
extern "C" [[gnu::optimize("omit-frame-pointer")]] int64_t extern "C" [[gnu::optimize("omit-frame-pointer")]] int64_t
system_time_nsecs() system_time_nsecs()
{ {
__uint128_t t = static_cast<__uint128_t>(rdtsc()) * cv_factor_nsec; __uint128_t t = static_cast<__uint128_t>(__rdtsc()) * cv_factor_nsec;
return t >> 32; return t >> 32;
} }