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 +++
让我困惑的是：
0x7f785c40f000结尾的行是什么意思/做什么？3949248 mmap为libc.so时，1840928为什么mprotect？mmap中使用的地址来自哪里？NULL中使用的地址来自何处mmap？arch_prctl之前XmlDocument doc = new XmlDocument();
using(var reader = XmlReader.Create(inputxmlPath, readerSettings))
doc.Load(reader);
分配的4k和8k内存是多少？答案 0 :(得分：0)
而是试着告诉你为什么使用那些确切的地址/大小（因为没有其他人回答），我想你可能想要一种方法来检查价值来自何处。您可以在加载器上使用gdb并在每个系统调用或特定系统调用处停止。假设您安装了debuginfos，您可以查看代码以查看值。这是一个例子：
$ gdb -q /lib64/ld-2.17.so
Reading symbols from /lib64/ld-2.17.so...Reading symbols from /usr/lib/debug/lib64/ld-2.17.so.debug...done.
done.
(gdb) b _start
Breakpoint 1 at 0x1430
(gdb) run ./a.out
Starting program: /lib64/ld-2.17.so ./a.out
Breakpoint 1, 0x0000555555555430 in _start ()
(gdb) p getpid()
$1 = 18102
(gdb) !cat /proc/18102/maps
555555554000-555555575000 r-xp 00000000 ca:01 396014 /lib64/ld-2.17.so
555555775000-555555777000 rw-p 00021000 ca:01 396014 /lib64/ld-2.17.so
555555777000-555555778000 rw-p 00000000 00:00 0 [heap]
7ffff7ffb000-7ffff7ffd000 r--p 00000000 00:00 0 [vvar]
7ffff7ffd000-7ffff7fff000 r-xp 00000000 00:00 0 [vdso]
7ffffffde000-7ffffffff000 rw-p 00000000 00:00 0 [stack]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
(gdb) catch syscall mmap
Catchpoint 2 (syscall 'mmap' [9])
(gdb) c
Continuing.
Catchpoint 2 (call to syscall mmap), 0x000055555556c6aa in mmap64 () at ../sysdeps/unix/syscall-template.S:81
81 T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
(gdb) fin
Run till exit from #0 0x000055555556c6aa in mmap64 () at ../sysdeps/unix/syscall-template.S:81
Catchpoint 2 (returned from syscall mmap), 0x000055555556c6aa in mmap64 () at ../sysdeps/unix/syscall-template.S:81
81 T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
(gdb) !cat /proc/18102/maps
00400000-00401000 r-xp 00000000 ca:01 13014 /home/ec2-user/so/e1/a.out
555555554000-555555575000 r-xp 00000000 ca:01 396014 /lib64/ld-2.17.so
555555775000-555555777000 rw-p 00021000 ca:01 396014 /lib64/ld-2.17.so
555555777000-555555778000 rw-p 00000000 00:00 0 [heap]
7ffff7ffb000-7ffff7ffd000 r--p 00000000 00:00 0 [vvar]
7ffff7ffd000-7ffff7fff000 r-xp 00000000 00:00 0 [vdso]
7ffffffde000-7ffffffff000 rw-p 00000000 00:00 0 [stack]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
(gdb) c
Continuing.
[...]
Continuing.
Catchpoint 2 (call to syscall mmap), 0x000055555556c6aa in mmap64 () at ../sysdeps/unix/syscall-template.S:81
81 T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
(gdb) fin
Run till exit from #0 0x000055555556c6aa in mmap64 () at ../sysdeps/unix/syscall-template.S:81
Catchpoint 2 (returned from syscall mmap), 0x000055555556c6aa in mmap64 () at ../sysdeps/unix/syscall-template.S:81
81 T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
(gdb) !cat /proc/18102/maps
00400000-00401000 r-xp 00000000 ca:01 13014 /home/ec2-user/so/e1/a.out
00600000-00601000 rw-p 00000000 ca:01 13014 /home/ec2-user/so/e1/a.out
555555554000-555555575000 r-xp 00000000 ca:01 396014 /lib64/ld-2.17.so
555555775000-555555777000 rw-p 00021000 ca:01 396014 /lib64/ld-2.17.so
555555777000-555555778000 rw-p 00000000 00:00 0 [heap]
7ffff7c32000-7ffff7ff4000 r-xp 00000000 ca:01 396021 /lib64/libc-2.17.so
7ffff7ff4000-7ffff7ffa000 r--p 00000000 ca:01 305615 /etc/ld.so.cache
7ffff7ffa000-7ffff7ffb000 rw-p 00000000 00:00 0
7ffff7ffb000-7ffff7ffd000 r--p 00000000 00:00 0 [vvar]
7ffff7ffd000-7ffff7fff000 r-xp 00000000 00:00 0 [vdso]
7ffffffde000-7ffffffff000 rw-p 00000000 00:00 0 [stack]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
(gdb) bt
#0 0x000055555556c6aa in mmap64 () at ../sysdeps/unix/syscall-template.S:81
#1 0x000055555555a45f in _dl_map_object_from_fd (name=name@entry=0x4002a1 "libc.so.6", fd=7, fbp=fbp@entry=0x7fffffffdb78,
realname=0x7ffff7ffa640 "/lib64/libc.so.6", loader=loader@entry=0x555555777210, l_type=l_type@entry=1, mode=mode@entry=0,
stack_endp=stack_endp@entry=0x7fffffffdb70, nsid=nsid@entry=0) at dl-load.c:1295
#2 0x000055555555c49b in _dl_map_object (loader=0x555555777210, name=0x4002a1 "libc.so.6", type=1, trace_mode=0, mode=<optimized out>, nsid=<optimized out>)
at dl-load.c:2374
#3 0x0000555555560992 in openaux (a=a@entry=0x7fffffffe128) at dl-deps.c:63
#4 0x00005555555631b4 in _dl_catch_error (objname=objname@entry=0x7fffffffe120, errstring=errstring@entry=0x7fffffffe118,
mallocedp=mallocedp@entry=0x7fffffffe110, operate=operate@entry=0x555555560960 <openaux>, args=args@entry=0x7fffffffe128) at dl-error.c:177
#5 0x0000555555561092 in _dl_map_object_deps (map=<optimized out>, preloads=<optimized out>, npreloads=<optimized out>, trace_mode=<optimized out>,
open_mode=<optimized out>) at dl-deps.c:256
#6 0x00005555555572c5 in dl_main (phdr=<optimized out>, phdr@entry=0x555555554040, phnum=<optimized out>, phnum@entry=7,
user_entry=user_entry@entry=0x7fffffffe2b8, auxv=<optimized out>) at rtld.c:1727
#7 0x000055555556a7d5 in _dl_sysdep_start (start_argptr=<optimized out>, dl_main=0x555555555a70 <dl_main>) at ../elf/dl-sysdep.c:244
#8 0x0000555555558cc1 in _dl_start_final (arg=0x7fffffffe370) at rtld.c:318
#9 _dl_start (arg=0x7fffffffe370) at rtld.c:544
#10 0x0000555555555438 in _start ()