考虑代码：
#include <stdio.h>
#include <stdlib.h>
int update (int *arr, int size);
#define SIZE 10
int main() { // <---------------------- Breakpoint 1
int x[SIZE];
// Initialize array
for (int c = 0 ; c < SIZE ; c++) {
x[c] = c * 2;
}
// Do some random updates to an array
update((int*) &x, SIZE);
// Print the elements
for (int c = 0 ; c < SIZE ; c++) {
printf("%d\n", x[c]);
}
return EXIT_SUCCESS;
} // <----------------------Breakpoint 2
int update (int *arr, int size) {
for (int i = 0 ; i < size ; i++) {
arr[i] += i;
update(arr+i, size-1);
}
return 1;
}
在断点1处运行info frame的结果：
Stack level 0, frame at 0x7ffc176b2610:
rip = 0x56434b0d76b8 in main (array.c:12); saved rip = 0x7f8190fb92b1
source language c.
Arglist at 0x7ffc176b2600, args:
Locals at 0x7ffc176b2600, Previous frame's sp is 0x7ffc176b2610
Saved registers:
rbp at 0x7ffc176b2600, rip at 0x7ffc176b2608
在断点2处运行info frame的结果：
Stack level 0, frame at 0x7ffc176b2610:
rip = 0x56434b0d771a in main (array.c:24); saved rip = 0x2d28490fd6501
source language c.
Arglist at 0x7ffc176b2600, args:
Locals at 0x7ffc176b2600, Previous frame's sp is 0x7ffc176b2610
Saved registers:
rbp at 0x7ffc176b2600, rip at 0x7ffc176b2608
我们发现main()已保存的返回地址rip at 0x7ffc176b2608在两个断点之间从0x7f8190fb92b1变为0x2d28490fd6501。
但是，使用rip在watch * 0x7ffc176b2608的地址上设置监视点并重新运行可执行文件不会按预期暂停断点之间的执行。
这怎么可能？
----------- ----------- EDIT
disassemble /s main的输出：
Dump of assembler code for function main:
array.c:
8 int main() {
0x000056434b0d76b0 <+0>: push rbp
0x000056434b0d76b1 <+1>: mov rbp,rsp
0x000056434b0d76b4 <+4>: sub rsp,0x30
9 int x[SIZE];
10
11 // Initialize array
12 for (int c = 0 ; c < SIZE ; c++) {
0x000056434b0d76b8 <+8>: mov DWORD PTR [rbp-0x4],0x0
0x000056434b0d76bf <+15>: jmp 0x56434b0d76d4 <main+36>
13 x[c] = c * 2;
0x000056434b0d76c1 <+17>: mov eax,DWORD PTR [rbp-0x4]
0x000056434b0d76c4 <+20>: lea edx,[rax+rax*1]
0x000056434b0d76c7 <+23>: mov eax,DWORD PTR [rbp-0x4]
0x000056434b0d76ca <+26>: cdqe
0x000056434b0d76cc <+28>: mov DWORD PTR [rbp+rax*4-0x30],edx
12 for (int c = 0 ; c < SIZE ; c++) {
0x000056434b0d76d0 <+32>: add DWORD PTR [rbp-0x4],0x1
0x000056434b0d76d4 <+36>: cmp DWORD PTR [rbp-0x4],0x9
0x000056434b0d76d8 <+40>: jle 0x56434b0d76c1 <main+17>
14 }
15
16 // Do some random updates to an array
17 update((int*) &x, SIZE);
0x000056434b0d76da <+42>: lea rax,[rbp-0x30]
0x000056434b0d76de <+46>: mov esi,0xa
0x000056434b0d76e3 <+51>: mov rdi,rax
0x000056434b0d76e6 <+54>: call 0x56434b0d7721 <update>
18
19 // Print the elements
20 for (int c = 0 ; c < SIZE ; c++) {
0x000056434b0d76eb <+59>: mov DWORD PTR [rbp-0x8],0x0
0x000056434b0d76f2 <+66>: jmp 0x56434b0d7714 <main+100>
21 printf("%d\n", x[c]);
0x000056434b0d76f4 <+68>: mov eax,DWORD PTR [rbp-0x8]
0x000056434b0d76f7 <+71>: cdqe
0x000056434b0d76f9 <+73>: mov eax,DWORD PTR [rbp+rax*4-0x30]
0x000056434b0d76fd <+77>: mov esi,eax
0x000056434b0d76ff <+79>: lea rdi,[rip+0x12e] # 0x56434b0d7834
0x000056434b0d7706 <+86>: mov eax,0x0
0x000056434b0d770b <+91>: call 0x56434b0d7560 <printf@plt>
20 for (int c = 0 ; c < SIZE ; c++) {
0x000056434b0d7710 <+96>: add DWORD PTR [rbp-0x8],0x1
0x000056434b0d7714 <+100>: cmp DWORD PTR [rbp-0x8],0x9
0x000056434b0d7718 <+104>: jle 0x56434b0d76f4 <main+68>
22 }
23
24 return EXIT_SUCCESS;
=> 0x000056434b0d771a <+106>: mov eax,0x0
25 }
0x000056434b0d771f <+111>: leave
0x000056434b0d7720 <+112>: ret
End of assembler dump.
disassemble /s update的输出：
Dump of assembler code for function update:
array.c:
27 int update (int *arr, int size) {
0x000056434b0d7721 <+0>: push rbp
0x000056434b0d7722 <+1>: mov rbp,rsp
0x000056434b0d7725 <+4>: sub rsp,0x20
0x000056434b0d7729 <+8>: mov QWORD PTR [rbp-0x18],rdi
0x000056434b0d772d <+12>: mov DWORD PTR [rbp-0x1c],esi
28 for (int i = 0 ; i < size ; i++) {
0x000056434b0d7730 <+15>: mov DWORD PTR [rbp-0x4],0x0
0x000056434b0d7737 <+22>: jmp 0x56434b0d7793 <update+114>
29 arr[i] += i;
0x000056434b0d7739 <+24>: mov eax,DWORD PTR [rbp-0x4]
0x000056434b0d773c <+27>: cdqe
0x000056434b0d773e <+29>: lea rdx,[rax*4+0x0]
0x000056434b0d7746 <+37>: mov rax,QWORD PTR [rbp-0x18]
0x000056434b0d774a <+41>: add rax,rdx
0x000056434b0d774d <+44>: mov edx,DWORD PTR [rbp-0x4]
0x000056434b0d7750 <+47>: movsxd rdx,edx
0x000056434b0d7753 <+50>: lea rcx,[rdx*4+0x0]
0x000056434b0d775b <+58>: mov rdx,QWORD PTR [rbp-0x18]
0x000056434b0d775f <+62>: add rdx,rcx
0x000056434b0d7762 <+65>: mov ecx,DWORD PTR [rdx]
0x000056434b0d7764 <+67>: mov edx,DWORD PTR [rbp-0x4]
0x000056434b0d7767 <+70>: add edx,ecx
0x000056434b0d7769 <+72>: mov DWORD PTR [rax],edx
30 update(arr+i, size-1);
0x000056434b0d776b <+74>: mov eax,DWORD PTR [rbp-0x1c]
0x000056434b0d776e <+77>: lea edx,[rax-0x1]
0x000056434b0d7771 <+80>: mov eax,DWORD PTR [rbp-0x4]
0x000056434b0d7774 <+83>: cdqe
0x000056434b0d7776 <+85>: lea rcx,[rax*4+0x0]
0x000056434b0d777e <+93>: mov rax,QWORD PTR [rbp-0x18]
0x000056434b0d7782 <+97>: add rax,rcx
0x000056434b0d7785 <+100>: mov esi,edx
0x000056434b0d7787 <+102>: mov rdi,rax
0x000056434b0d778a <+105>: call 0x56434b0d7721 <update>
28 for (int i = 0 ; i < size ; i++) {
0x000056434b0d778f <+110>: add DWORD PTR [rbp-0x4],0x1
0x000056434b0d7793 <+114>: mov eax,DWORD PTR [rbp-0x4]
0x000056434b0d7796 <+117>: cmp eax,DWORD PTR [rbp-0x1c]
0x000056434b0d7799 <+120>: jl 0x56434b0d7739 <update+24>
31 }
32 return 1;
0x000056434b0d779b <+122>: mov eax,0x1
33 }
0x000056434b0d77a0 <+127>: leave
0x000056434b0d77a1 <+128>: ret
End of assembler dump.
~/.gdbinit
# Security
set auto-load safe-path /
# Misc
set disassembly-flavor intel
set disable-randomization off
set pagination off
set follow-fork-mode child
# History
set history filename ~/.gdbhistory
set history save
set history expansion
disp/10i $pc
handle SIGXCPU SIG33 SIG35 SIGPWR nostop noprint
set tui enable
答案 0 :(得分：1)
.gdbinit中的这一行可能是您遇到问题的根源：
set disable-randomization off
默认情况下，GDB禁用地址空间布局随机化（ASLR）。这意味着GDB下的二进制文件从完全相同的地址开始，每次运行时都有完全相同的堆栈指针。这默认为正好，因此您可以在给定地址上设置观察点和断点，并在每次运行时触发它。
通过设置disable-randomization，您要求GDB以与在GDB之外运行相同的方式运行二进制文件，即启用ASLR。现在堆栈变量的位置（以及你拥有的PIE binary的全局变量）将从一次运行更改为运行，并且在给定的堆栈地址上设置一个观察点只能随机而且很少。
您可以多次发出info frame和run来确认这是原因。您将观察到保存寄存器的位置在运行之间发生变化。
TL; DR：不要将您不熟悉的设置放入.gdbinit。
答案 1 :(得分：-1)
代码的问题是堆栈的破坏。
@Mark Plotnick的评论澄清了问题，并提出了如何解决问题的建议。