【发布时间】：2016-02-09 12:19:29
【问题描述】：
int main(int argc, char *argv[])
{
return 0;
}
鉴于上述 C 程序，我使用 clang test.c ; strace ./a.out 得到以下输出。
execve("./a.out", ["./a.out"], [/* 36 vars */]) = 0
brk(0) = 0x1a06000
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) = 0x7f785c40f000
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=78590, ...}) = 0
mmap(NULL, 78590, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f785c3fb000
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\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\320\37\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1840928, ...}) = 0
mmap(NULL, 3949248, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f785be2a000
mprotect(0x7f785bfe5000, 2093056, PROT_NONE) = 0
mmap(0x7f785c1e4000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1ba000) = 0x7f785c1e4000
mmap(0x7f785c1ea000, 17088, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f785c1ea000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f785c3fa000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f785c3f8000
arch_prctl(ARCH_SET_FS, 0x7f785c3f8740) = 0
mprotect(0x7f785c1e4000, 16384, PROT_READ) = 0
mprotect(0x600000, 4096, PROT_READ) = 0
mprotect(0x7f785c411000, 4096, PROT_READ) = 0
munmap(0x7f785c3fb000, 78590) = 0
exit_group(0) = ?
+++ exited with 0 +++
有件事让我很困惑：
- 以
0x7f785c40f000结尾的行是什么意思？ - 当
libc.so是1840928很大时，为什么3949248在mmap中？ -
mprotect中使用的地址来自哪里？ -
mmap中使用的地址不是NULL时从何而来？ -
mmap在arch_prctl之前分配的4k和8k内存是什么？
【问题讨论】：
-
好问题。以上应该几乎都是动态加载器的工作，它有一个相当复杂的规范。将它与
-static构建进行比较会很有趣，其中大部分内容不会发生，但其他会发生（例如uname调用和一些brk调用但没有mmaps）。跨度> -
@PSkocik 是的，结果就是这样：paste.ubuntu.com/15001856