在上一篇文章中讲到了ptrace，那么我们完全可以用ptrace来写一个非常简单的trace工具，用以trace程序的具体运行过程。
用它可以很清楚的回答，使用glibc编译后的hello world是从什么地方开始运行的。
(注：本文内容根据“A really simple tracing debugger"翻译而来，具体链接见参考资料一节)
itrace.c
#include <stdio.h>
#include <sys/wait.h>
#include <unistd.h> #include <sys/user.h>
#include <sys/ptrace.h> int main(int argc, char **argv)
{
int pid = fork();
if(pid == ) {
if(ptrace(PTRACE_TRACEME) < ) {
perror("ptrace");
_exit();
}
execvp(argv[], argv + );
perror("exec");
_exit();
}
while() {
int status;
struct user_regs_struct regs;
if(waitpid(pid, &status, ) < )
perror("waitpid");
if(!WIFSTOPPED(status))
break;
if(ptrace(PTRACE_GETREGS, pid, , ®s) < )
perror("ptrace/GETREGS");
printf("%lx %lx\n", regs.eip, regs.esp);
if(ptrace(PTRACE_SINGLESTEP, pid, , ) < )
perror("ptrace/SINGLESTEP");
}
return ;
}
编译
gcc -m32 itrace.c -o itrace
译者注: -m32表示编译成32位格式，如果是在64位机器上，不需要加此选项，同时将itrace.c源码中的eip和esp转换为rip,rsp.
hellow.c
#include <stdio.h>
int main() {
printf("Hello, world!\n");
return ;
}
编译
gcc -static -o hellow hellow.c
译者注: itrace保持一致，itrace如果是按32位格式来编译的，此处也应该一样。
测试运行
./itrace ./hellow | addr2line -e ./hellow -f | grep -v "??\|:?" | uniq
说明如下
addr2line 是将地址转换为相应的源码
运行的结果很长，所以就不打算没有贴出来了。
treeify
为了让运行结果在显示的时候能够更好的反映出调用关系，根据堆栈(%esp)中的信息采用python脚本将其层次化的打印出来。
import subprocess
import sys def read():
for line in sys.stdin:
try:
regs = [int(x, 16) for x in line.split(" ")]
yield {"eip": regs[0], "esp": regs[1]}
# Ignore lines interspersed with other output!
except (ValueError, IndexError):
pass def addr2line(iterable):
proc = subprocess.Popen(["addr2line", "-e", sys.argv[1], "-f"],
stdin=subprocess.PIPE, stdout=subprocess.PIPE)
for regs in iterable:
proc.stdin.write("%x\n" % regs["eip"])
a = proc.stdout.readline().rstrip("\n")
b = proc.stdout.readline().rstrip("\n")
regs["func"] = "%s %s" % (a, b)
yield regs def entry_points(iterable):
funcs = {}
# We treat the first address we see for the function as its entry
# point, and only report those entries from this point on.
for regs in iterable:
func = regs["func"].split(":")[0]
if funcs.setdefault(func, regs["eip"]) == regs["eip"]:
yield regs def add_nesting(iterable):
stack = [2 ** 64]
for regs in iterable:
stack_pos = regs["esp"]
if stack_pos < stack[-1]:
stack.append(stack_pos)
while stack_pos > stack[-1]:
stack.pop()
regs["indent"] = " " * len(stack)
yield regs for x in add_nesting(entry_points(addr2line(read()))):
print x["indent"], x["func"], "%x" % x["eip"]
运行
./itrace ./hellow|python2 ./treeify.py ./hellow
测试结果
_start /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/start.S: 8048d40
__libc_start_main ??:? 8048ea0
_dl_aux_init ??:? 806e590
_dl_discover_osversion ??:? 806f3b0
uname ??:? 80921c0
?? ??: b77e0414
index ??:? 805b250
__x86.get_pc_thunk.bx /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S: 8048d70
__init_cpu_features ??:? 806f570
strncasecmp_l ??:? 80b5ac0
strcmp ??:? 805b460
memset ??:? 805ba70
strcasecmp_l ??:? 805bc10
bcmp ??:? 805b6b0
strstr ??:? 806b080
memchr ??:? 808ce90
__x86.get_pc_thunk.bx /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S: 8048d70
strrchr ??:? 808c660
__x86.get_pc_thunk.bx /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S: 8048d70
wcslen ??:? 808eae0
__x86.get_pc_thunk.bx /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S: 8048d70
__rawmemchr ??:? 805bcc0
__x86.get_pc_thunk.bx /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S: 8048d70
memmove ??:? 805b9d0
__strnlen ??:? 808c620
__x86.get_pc_thunk.bx /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S: 8048d70
strcpy ??:? 805b4d0
stpcpy ??:? 805bb30
__pthread_initialize_minimal ??:? 80494d0
__libc_setup_tls ??:?
sbrk ??:? 806cd70
__brk ??:? 80928e0
?? ??: b77e0414
__brk ??:? 80928e0
?? ??: b77e0414
memcpy ??:? 805bc50
__libc_init_first ??:? 806f4b0
__setfpucw ??:? 807ac00
__libc_init_secure ??:? 806f360
_dl_non_dynamic_init ??:? 806e7f0
_dl_get_origin ??:? 809a800
?? ??: b77e0414
malloc ??:? 8058f60
malloc_hook_ini malloc.o:? 805a020
ptmalloc_init.part. malloc.o:? 8059c20
__linkin_atfork ??:? 806e0f0
malloc ??:? 8058f60
_int_malloc malloc.o:?
malloc_consolidate malloc.o:? 80560b0
malloc_init_state malloc.o:? 80552e0
__default_morecore ??:? 805b230
sbrk ??:? 806cd70
__brk ??:? 80928e0
?? ??: b77e0414
__default_morecore ??:? 805b230
sbrk ??:? 806cd70
__brk ??:? 80928e0
?? ??: b77e0414
mempcpy ??:? 805bb00
getenv ??:? 804e240
strlen ??:? 805b5f0
_dl_new_object ??:? 80972a0
strlen ??:? 805b5f0
__calloc ??:?
_int_malloc malloc.o:?
__memset_sse2_rep ??:? 805f690
memcpy ??:? 805bc50
_dl_setup_hash ??:?
strlen ??:? 805b5f0
malloc ??:? 8058f60
_int_malloc malloc.o:?
memcpy ??:? 805bc50
_dl_add_to_namespace_list ??:?
getenv ??:? 804e240
strlen ??:? 805b5f0
_dl_init_paths ??:? 80951f0
_dl_important_hwcaps ??:? 80991b0
malloc ??:? 8058f60
_int_malloc malloc.o:?
mempcpy ??:? 805bb00
malloc ??:? 8058f60
_int_malloc malloc.o:?
malloc ??:? 8058f60
_int_malloc malloc.o:?
getenv ??:? 804e240
strlen ??:? 805b5f0
getenv ??:? 804e240
strlen ??:? 805b5f0
getenv ??:? 804e240
strlen ??:? 805b5f0
getenv ??:? 804e240
strlen ??:? 805b5f0
getenv ??:? 804e240
strlen ??:? 805b5f0
__init_misc ??:? 806dd90
__strrchr_sse2_bsf ??:? 808d830
__ctype_init ??:? 807abb0
__cxa_atexit ??:? 804e5d0
__new_exitfn ??:? 804e440
__libc_csu_init ??:? 80494f0
_init /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S:
__x86.get_pc_thunk.bx /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S: 8048d70
_init /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crtn.S: 80481ae
frame_dummy crtstuff.c:? 8048e20
__register_frame_info_bases ??:? 80bd5a0
__x86.get_pc_thunk.bx /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S: 8048d70
register_tm_clones crtstuff.c:? 8048db0
init_cacheinfo cacheinfo.o:? 8048b10
handle_intel cacheinfo.o:? 806b380
intel_check_word cacheinfo.o:? 806b0b0
intel_check_word cacheinfo.o:? 806b0b0
intel_check_word cacheinfo.o:? 806b0b0
intel_check_word cacheinfo.o:? 806b0b0
handle_intel cacheinfo.o:? 806b380
intel_check_word cacheinfo.o:? 806b0b0
intel_check_word cacheinfo.o:? 806b0b0
_setjmp ??:? 804d970
main ??:? 8048e7c
puts ??:? 804f350
strlen ??:? 805b5f0
_IO_new_file_xsputn ??:?
_IO_file_overflow ??:? 8052e60
_IO_doallocbuf ??:? 8053b10
_IO_file_doallocate ??:? 808a730
_IO_file_stat ??:? 8051f20
___fxstat64 ??:? 806c300
?? ??: b77e0414
__mmap ??:? 806ce60
?? ??: b77e0414
_IO_setb ??:? 8053aa0
_IO_new_do_write ??:? 80527b0
_IO_default_xsputn ??:? 8053bc0
exit ??:? 804e420
__run_exit_handlers ??:? 804e320
__libc_csu_fini ??:?
fini sdlerror.o:? 8048b00
check_free.isra. sdlerror.o:? 80a6f30
__do_global_dtors_aux crtstuff.c:? 8048df0
deregister_tm_clones crtstuff.c:? 8048d80
__deregister_frame_info_bases ??:? 80bd7c0
__x86.get_pc_thunk.bx /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S: 8048d70
_fini /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S: 80bec78
__x86.get_pc_thunk.bx /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crti.S: 8048d70
_fini /root/glibc/src/glibc-2.18/csu/../sysdeps/i386/crtn.S: 80bec87
_IO_cleanup ??:? 80543b0
_IO_flush_all_lockp ??:?
_IO_file_overflow ??:? 8052e60
_IO_new_do_write ??:? 80527b0
new_do_write fileops.o:?
_IO_file_write ??:? 8051f50
__write ??:? 806c420
?? ??: b77e0414
_IO_file_setbuf ??:?
_IO_default_setbuf ??:? 8053d10
_IO_file_sync ??:?
_IO_setb ??:? 8053aa0
_Exit ??:? 806ba24
?? ??: b77e0414