[英]how to call sys_open rather than sys_openat when calling open
我寫了一段代碼來生成系統調用
void open_test(int fd, const char *filepath) {
if (fd == -1) {
printf("Open \"%s\" Failed!\n", filepath);
} else {
printf("Successfully Open \"%s\"!\n", filepath);
write(fd, "successfully open!", sizeof("successfully open!") - 1);
close(fd);
}
fflush(stdout);
}
int main(int argc, char const *argv[]) {
const char fp1[] = "whatever.txt", fp2[] = "./not-exist.txt";
int fd1 = open(fp1, O_CREAT | O_WRONLY | O_TRUNC, S_IRWXU);
int fd2 = open(fp2, O_WRONLY | O_TRUNC, S_IRWXU);
open_test(fd1, fp1);
open_test(fd2, fp2);
return 0;
}
和另一個程序(細節省略)來捕捉系統調用,但后來我發現所有的open()
結果都是調用 sys_openat 而不是 sys_open。
以下文本是程序的輸出:
Detect system call open, %rax is 257, Addr is 0x00007fefef78aec8, Pathname is /etc/ld.so.cache
Detect system call open, %rax is 257, Addr is 0x00007fefef78aec8, Pathname is /etc/ld.so.cache
Detect system call open, %rax is 257, Addr is 0x00007fefef993dd0, Pathname is /lib/x86_64-linux-gnu/libc.so.6
Detect system call open, %rax is 257, Addr is 0x00007fefef993dd0, Pathname is /lib/x86_64-linux-gnu/libc.so.6
Detect system call open, %rax is 257, Addr is 0x00007fffd44e38e3, Pathname is whatever.txt
Detect system call open, %rax is 257, Addr is 0x00007fffd44e38e3, Pathname is whatever.txt
Detect system call open, %rax is 257, Addr is 0x00007fffd44e38f0, Pathname is ./not-exist.txt
Detect system call open, %rax is 257, Addr is 0x00007fffd44e38f0, Pathname is ./not-exist.txt
Successfully Open "whatever.txt"!
Open "./not-exist.txt" Failed!
這里 rax=257 表示調用了 sys_openat(對於 sys_open,rax=2)
您通過syscall(2)
包裝器syscall(SYS_open, ...)
: syscall(SYS_open, ...)
:
#define _GNU_SOURCE
#include <unistd.h>
#include <fcntl.h>
#include <err.h>
#include <sys/syscall.h>
int main(void){
char *path = "whatever.txt";
int fd = syscall(SYS_open, path, O_RDONLY, 0);
if(fd == -1) err(1, "SYS_open %s", path);
}
但何必呢? SYS_openat
現在是規范的系統調用, open(2)
只是一個 API,保留SYS_open
系統調用條目只是為了向后二進制兼容。
在較新的體系結構上,可能根本沒有實際的SYS_open
系統調用。
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