[hellogcc] Re: Fwd: Why running the next command will jump back to the previous line position
- From: asmwarrior <asmwarrior@xxxxxxxxx>
- To: hellogcc@xxxxxxxxxxxxx
- Date: Sat, 29 Oct 2011 21:46:25 +0800
On 2011-10-29 21:35, Yao Qi wrote:
这样的问题就是gcc在产生 debug info 不是很准确造成的。我没有办法在我的
gcc 4.4 上重现这个问题，但是我相信这个问题是存在的。
在dwarf里边，.debug_line这个段是用来记录把地址映射回到源代码
行号的。你可以用 readelf -wl 1.exe 看看，就能看明白。这样的问题一般
都是gcc 产生的debug info不对，虽然在也是gcc的bug，但是这样的bug优先级
比较低，所以，可能没有人修吧。
谢谢。我对dwarf是不太懂，今天去gcc help上面发了个贴，似乎没有人回答。
gdb的邮件列表里面有人回复了我，我用
objdump -dSC a.exe
这个命令输出了结果看了一下，我不太看得懂内容，但是从里面有一段话的情况来看，似乎同一个行号，对应了很多指令地址：
00401660<main>:
#include<string>
#include<map>
int main()
{
401660: 55 push %ebp
401661: 89 e5 mov %esp,%ebp
401663: 53 push %ebx
401664: 83 e4 f0 and $0xfffffff0,%esp
401667: 83 ec 40 sub $0x40,%esp
40166a: e8 c1 ca 00 00 call 40e130<__main>
std::map<int, std::string> m;
40166f: 8d 44 24 20 lea 0x20(%esp),%eax
401673: 89 04 24 mov %eax,(%esp)
401676: e8 3d aa 01 00 call 41c0b8<std::map<int, std::string, std::less<int>,
std::allocator<std::pair<int const, std::string> > >::map()>
m[0] = "000";
40167b: c7 44 24 38 00 00 00 movl $0x0,0x38(%esp)
401682: 00
401683: 8d 44 24 38 lea 0x38(%esp),%eax
401687: 89 44 24 04 mov %eax,0x4(%esp)
40168b: 8d 44 24 20 lea 0x20(%esp),%eax
40168f: 89 04 24 mov %eax,(%esp)
401692: e8 49 aa 01 00 call 41c0e0<std::map<int, std::string, std::less<int>,
std::allocator<std::pair<int const, std::string> > >::operator[](int&&)>
401697: c7 44 24 04 86 f0 41 movl $0x41f086,0x4(%esp)
40169e: 00
40169f: 89 04 24 mov %eax,(%esp)
4016a2: e8 a9 a6 01 00 call 41bd50<std::string::operator=(char
const*)>
m[1] = "111";
4016a7: c7 44 24 3c 01 00 00 movl $0x1,0x3c(%esp)
4016ae: 00
4016af: 8d 44 24 3c lea 0x3c(%esp),%eax
4016b3: 89 44 24 04 mov %eax,0x4(%esp)
4016b7: 8d 44 24 20 lea 0x20(%esp),%eax
4016bb: 89 04 24 mov %eax,(%esp)
4016be: e8 1d aa 01 00 call 41c0e0<std::map<int, std::string, std::less<int>,
std::allocator<std::pair<int const, std::string> > >::operator[](int&&)>
4016c3: c7 44 24 04 8a f0 41 movl $0x41f08a,0x4(%esp)
4016ca: 00
4016cb: 89 04 24 mov %eax,(%esp)
4016ce: e8 7d a6 01 00 call 41bd50<std::string::operator=(char
const*)>
for( int i = 0; i< 3; i++)
4016d3: c7 44 24 1c 00 00 00 movl $0x0,0x1c(%esp)
4016da: 00
4016db: eb 2f jmp 40170c<main+0xac>
{
m[i] = "ssss";
4016dd: 8d 44 24 1c lea 0x1c(%esp),%eax
4016e1: 89 44 24 04 mov %eax,0x4(%esp)
4016e5: 8d 44 24 20 lea 0x20(%esp),%eax
4016e9: 89 04 24 mov %eax,(%esp)
4016ec: e8 1f ab 01 00 call 41c210<std::map<int, std::string, std::less<int>,
std::allocator<std::pair<int const, std::string> > >::operator[](int const&)>
4016f1: c7 44 24 04 8e f0 41 movl $0x41f08e,0x4(%esp)
4016f8: 00
4016f9: 89 04 24 mov %eax,(%esp)
4016fc: e8 4f a6 01 00 call 41bd50<std::string::operator=(char
const*)>
int main()
{
std::map<int, std::string> m;
m[0] = "000";
m[1] = "111";
for( int i = 0; i< 3; i++)
401701: 8b 44 24 1c mov 0x1c(%esp),%eax
401705: 83 c0 01 add $0x1,%eax
401708: 89 44 24 1c mov %eax,0x1c(%esp)
40170c: 8b 44 24 1c mov 0x1c(%esp),%eax
401710: 83 f8 02 cmp $0x2,%eax
401713: 0f 9e c0 setle %al
401716: 84 c0 test %al,%al
401718: 75 c3 jne 4016dd<main+0x7d>
{
m[i] = "ssss";
}
return 0;
40171a: bb 00 00 00 00 mov $0x0,%ebx
#include<string>
#include<map>
int main()
{
std::map<int, std::string> m;
40171f: 8d 44 24 20 lea 0x20(%esp),%eax
401723: 89 04 24 mov %eax,(%esp)
401726: e8 a1 a9 01 00 call 41c0cc<std::map<int, std::string, std::less<int>,
std::allocator<std::pair<int const, std::string> > >::~map()>
40172b: 89 d8 mov %ebx,%eax
for( int i = 0; i< 3; i++)
{
m[i] = "ssss";
}
return 0;
}
40172d: 8b 5d fc mov -0x4(%ebp),%ebx
401730: c9 leave
401731: c3 ret
401732: 89 c3 mov %eax,%ebx
#include<string>
#include<map>
int main()
{
std::map<int, std::string> m;
401734: 8d 44 24 20 lea 0x20(%esp),%eax
401738: 89 04 24 mov %eax,(%esp)
40173b: e8 8c a9 01 00 call 41c0cc<std::map<int, std::string, std::less<int>,
std::allocator<std::pair<int const, std::string> > >::~map()>
401740: 89 d8 mov %ebx,%eax
401742: 89 04 24 mov %eax,(%esp)
401745: e8 26 f4 00 00 call 410b70<_Unwind_Resume>
40174a: 90 nop
40174b: 90 nop
40174c: 00 00 add %al,(%eax)
...
上面这段话的意思，是不是说：当return语句之后，接下来的语句，又跳回到main的开头行号了？
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