#include

#include

int main()

{

struct timespec ts;

fprintf(stderr, "start!\n");

clock_gettime(CLOCK_REALTIME, &ts);

fprintf(stderr, "realtime %lu %lu\n", ts.tv_sec, ts.tv_nsec);

clock_gettime(CLOCK_MONOTONIC, &ts);

fprintf(stderr, "monotonic %lu %lu\n", ts.tv_sec, ts.tv_nsec);

return 0;

}

我得到这个：

execve("/tmp/x", ["/tmp/x"], [/* 72 vars */]) = 0

brk(NULL) = 0x13d0000

access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)

mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fed9a0d1000

access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)

open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3

fstat(3, {st_mode=S_IFREG|0644, st_size=126501, ...}) = 0

mmap(NULL, 126501, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fed9a0b2000

close(3) = 0

access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)

open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3

read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P\t\2\0\0\0\0\0"..., 832) = 832

fstat(3, {st_mode=S_IFREG|0755, st_size=1864888, ...}) = 0

mmap(NULL, 3967488, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fed99ae5000

mprotect(0x7fed99ca5000, 2093056, PROT_NONE) = 0

mmap(0x7fed99ea4000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1bf000) = 0x7fed99ea4000

mmap(0x7fed99eaa000, 14848, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fed99eaa000

close(3) = 0

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fed9a0b1000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fed9a0b0000

mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fed9a0af000

arch_prctl(ARCH_SET_FS, 0x7fed9a0b0700) = 0

mprotect(0x7fed99ea4000, 16384, PROT_READ) = 0

mprotect(0x600000, 4096, PROT_READ) = 0

mprotect(0x7fed9a0d3000, 4096, PROT_READ) = 0

munmap(0x7fed9a0b2000, 126501) = 0

write(2, "start!\n", 7start!

) = 7

write(2, "realtime 1488919932 97097045\n", 29realtime 1488919932 97097045

) = 29

write(2, "monotonic 258985 170149836\n", 27monotonic 258985 170149836

) = 27

exit_group(0) = ?

+++ exited with 0 +++

似乎有不被系统调用涉及制备任CLOCK_REALTIME或CLOCK_MONOTONIC值。这是如何实施的？我试图用汇编语言来介绍它，但是我一定没有注意到关键部分，因为我无法弄清楚它是如何完成的。