我编写了一个简单的程序,如下所示,并进行了strace跟踪。
#include<stdio.h>
int foo(int i)
{
int k=9;
if(i==10)
return 1;
else
foo(++i);
open("1",1);
}
int main()
{
foo(1);
}
我这么做的目的是检查函数中变量(此例中为 int k)在栈上分配内存的情况。我使用了一个开放系统调用作为标记。strace 的输出如下:
execve("./a.out", ["./a.out"], [/* 25 vars */]) = 0
brk(0) = 0x8653000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb777e000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat64(3, {st_mode=S_IFREG|0644, st_size=95172, ...}) = 0
mmap2(NULL, 95172, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7766000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/i386-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0000\226\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0755, st_size=1734120, ...}) = 0
mmap2(NULL, 1743580, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb75bc000
mmap2(0xb7760000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1a4) = 0xb7760000
mmap2(0xb7763000, 10972, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb7763000
close(3) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb75bb000
set_thread_area({entry_number:-1 -> 6, base_addr:0xb75bb900, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0
mprotect(0xb7760000, 8192, PROT_READ) = 0
mprotect(0x8049000, 4096, PROT_READ) = 0
mprotect(0xb77a1000, 4096, PROT_READ) = 0
munmap(0xb7766000, 95172) = 0
open("1", O_WRONLY) = -1 ENOENT (No such file or directory)
open("1", O_WRONLY) = -1 ENOENT (No such file or directory)
open("1", O_WRONLY) = -1 ENOENT (No such file or directory)
open("1", O_WRONLY) = -1 ENOENT (No such file or directory)
open("1", O_WRONLY) = -1 ENOENT (No such file or directory)
open("1", O_WRONLY) = -1 ENOENT (No such file or directory)
open("1", O_WRONLY) = -1 ENOENT (No such file or directory)
open("1", O_WRONLY) = -1 ENOENT (No such file or directory)
open("1", O_WRONLY) = -1 ENOENT (No such file or directory)
exit_group(-1) = ?
在strace输出的末尾,您可以看到在open系统调用之间没有调用任何系统调用。那么,在没有系统调用的情况下,如何为被调用的函数分配堆栈上的内存?
strace
的一条严重注意事项:strace
无法显示使用dl_open()
打开的库。 - PersianGulf