我正在做一些功课，我需要报告一个C程序利用了哪些系统调用。
不过我注意到 exit 不见得 strace 报告。
#include <stdlib.h>
int main() {
exit(0);
}
┌─[brendon@parrot]─[~/Desktop/Classes/OSInternals/Lab3]
└──╼ $gcc exit.c
┌─[brendon@parrot]─[~/Desktop/Classes/OSInternals/Lab3]
└──╼ $strace -c ./a.out
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
38.74 0.001056 150 7 mmap
11.12 0.000303 151 2 openat
10.20 0.000278 139 2 fstat
10.09 0.000275 137 2 close
9.21 0.000251 251 1 arch_prctl
7.45 0.000203 67 3 mprotect
6.20 0.000169 169 1 munmap
5.25 0.000143 143 1 read
1.76 0.000048 48 1 1 access
0.00 0.000000 0 1 brk
0.00 0.000000 0 1 execve
------ ----------- ----------- --------- --------- ----------------
100.00 0.002726 22 1 total
如你所见。exit 不显示在报告中。难道我说错了，是系统调用？阅读 usr/include/x86_64-linux-gnu/asm/unistd_64.h，我可以看到一个 exit 条目。
. . .
#define __NR_execve 59
#define __NR_exit 60
#define __NR_wait4 61
. . .
我错过了什么？
在Parrot OS上运行。
我很犹豫要不要发这个帖子，因为不清楚这是否够主题。如果认定不符合主题，我可以及时删除。
由于某些原因，它没有出现在 -c 摘要，但它确实显示在常规的 strace 产量。
#include <stdlib.h>
int main(void)
{
exit(69);
}
$ strace ./exit
execve("./exit", ["./exit"], 0x7ffddc502ce0 /* 42 vars */) = 0
brk(NULL) = 0x563a56e63000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=113870, ...}) = 0
mmap(NULL, 113870, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f16c8537000
close(3) = 0
openat(AT_FDCWD, "/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\0\260A\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1824496, ...}) = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f16c8535000
mmap(NULL, 1837056, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f16c8374000
mprotect(0x7f16c8396000, 1658880, PROT_NONE) = 0
mmap(0x7f16c8396000, 1343488, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x22000) = 0x7f16c8396000
mmap(0x7f16c84de000, 311296, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x16a000) = 0x7f16c84de000
mmap(0x7f16c852b000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b6000) = 0x7f16c852b000
mmap(0x7f16c8531000, 14336, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f16c8531000
close(3) = 0
arch_prctl(ARCH_SET_FS, 0x7f16c8536500) = 0
mprotect(0x7f16c852b000, 16384, PROT_READ) = 0
mprotect(0x563a565ba000, 4096, PROT_READ) = 0
mprotect(0x7f16c857a000, 4096, PROT_READ) = 0
munmap(0x7f16c8537000, 113870) = 0
exit_group(69) = ?
+++ exited with 69 +++
$ strace -c ./exit
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
0.00 0.000000 0 1 read
0.00 0.000000 0 2 close
0.00 0.000000 0 2 fstat
0.00 0.000000 0 7 mmap
0.00 0.000000 0 4 mprotect
0.00 0.000000 0 1 munmap
0.00 0.000000 0 1 brk
0.00 0.000000 0 1 1 access
0.00 0.000000 0 1 execve
0.00 0.000000 0 1 arch_prctl
0.00 0.000000 0 2 openat
------ ----------- ----------- --------- --------- ----------------
100.00 0.000000 23 1 total
鉴于 -c 衡量 时候 在每次系统调用中所花费的时间，我猜测它没有任何意义来衡量。exit (永远不会回来)。