Osheep

时光不回头,当下最重要。

gcc AddressSanitizer

程序中发生内存相关的问题,向来都是让人头大的。这里介绍一下ASan相关的内容,希望可以对debug内存相关的问题有所帮助。

ASan相关的简介可以参考wiki:https://en.wikipedia.org/wiki/AddressSanitizer

ASan在clang(3.1之后)和gcc(4.8之后)均支持,以下以gcc举例:

int main(int argc ,char **argv)
{
    int stack_array[100];
    stack_array[1] = 100;
    return stack_array[argc + 100];
}

g++ -g -fsanitize=address main.cpp

编译好后,运行

./a.out
=================================================================
==7163==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fff9666ccd4 at pc 0x000000400906 bp 0x7fff9666cb00 sp 0x7fff9666caf0
READ of size 4 at 0x7fff9666ccd4 thread T0
    #0 0x400905 in main /home/tsing/asan/main.cpp:5
    #1 0x7f199d0e982f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
    #2 0x400748 in _start (/home/tsing/asan/a.out+0x400748)

Address 0x7fff9666ccd4 is located in stack of thread T0 at offset 436 in frame
    #0 0x400825 in main /home/tsing/asan/main.cpp:2

  This frame has 1 object(s):
    [32, 432) 'stack_array' <== Memory access at offset 436 overflows this variable
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow /home/tsing/asan/main.cpp:5 main
Shadow bytes around the buggy address:
  0x100072cc5940: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100072cc5950: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100072cc5960: 00 00 00 00 f1 f1 f1 f1 00 00 00 00 00 00 00 00
  0x100072cc5970: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100072cc5980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x100072cc5990: 00 00 00 00 00 00 00 00 00 00[f4]f4 f3 f3 f3 f3
  0x100072cc59a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100072cc59b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100072cc59c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100072cc59d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100072cc59e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
==7163==ABORTING

运行程序,会把越界访问地方的call stack打印出来。

gcc -fsanitize选项真的非常强大,heap区动态申请的内存、全局data段的内存,均可以被侦测到。另外-fsanitize选项较多,具体可以参考gcc的手册:
https://gcc.gnu.org/onlinedocs/
强烈建议备一份。这些选项包括内存泄漏的检测,多线程临界资源监测等等。

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