execve如何调用动态链接器/加载器(ld-linux.so.2)

Question

我用gcc编译并链接了最基本的C程序test.c:

int
main() {
}

正如所料,输出是动态链接的可执行文件:

$ file test
test: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses     shared libs), for GNU/Linux 2.6.26, BuildID[sha1]=0x0f806c099f74132a158d98aebde4639ae0998971, not stripped

运行strace提供以下输出:

$ strace -f ./test
execve("./test", ["./test"], [/* 31 vars */]) = 0
brk(0)                                  = 0x248d000
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) = 0x7f77eeb27000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY)      = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=109292, ...}) = 0
mmap(NULL, 109292, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f77eeb0c000
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) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\357\1\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1595408, ...}) = 0
mmap(NULL, 3709016, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f77ee580000
mprotect(0x7f77ee700000, 2097152, PROT_NONE) = 0
mmap(0x7f77ee900000, 20480, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x180000) = 0x7f77ee900000
mmap(0x7f77ee905000, 18520, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f77ee905000
close(3)                                = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f77eeb0b000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f77eeb0a000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f77eeb09000
arch_prctl(ARCH_SET_FS, 0x7f77eeb0a700) = 0
mprotect(0x7f77ee900000, 16384, PROT_READ) = 0
mprotect(0x7f77eeb29000, 4096, PROT_READ) = 0
munmap(0x7f77eeb0c000, 109292)          = 0
exit_group(-292524312)                  = ?

因为根据execve手册,我期待在strace输出中的某处看到"/lib64/ld-linux.so.2":

如果可执行文件是动态链接的ELF可执行文件,则在PT_INTERP段中命名的解释器用于加载所需的共享库.对于与glibc 2链接的二进制文件,此解释器>通常为/lib/ld-linux.so.2

我的猜测是链接器/加载器(/lib64/ld-linux.so.2)调用是execve的一部分.有人可以证实吗？

Answer 1

我的猜测是链接器/加载器(/lib64/ld-linux.so.2)调用是execve的一部分.

这有点正确.

内核首先查看主要的可执行段,然后将mmap它们放入新的"进程shell"中.

当它发现可执行文件有PT_INTERP段时,它也是mmap该文件的段,并将控制传递给它.

因此,在"返回" execve()进入用户模式后,解释器(通常/lib64/ld-linux-x86-64.so.2在Linux/x86_64上)已经映射并运行.然后,该解释器的工作是将其自身重新定位到mmap其余所需的共享库,初始化它们,最后将控制转移到主可执行文件.

如果您想了解更多细节,请从此处开始.