c++ - gdb - 查找 strncmp() 函数的值

Question

我有一个代码遇到了 strncmp() 的段错误，我在下面有这个信息:

#7  0x00007f3662e5d4e7 in __strncmp_sse42 () from /lib64/libc.so.6
(gdb) info locals
No symbol table info available.
(gdb) info args
No symbol table info available.
(gdb) info frame
Stack level 7, frame at 0x7f35f4413b70:
 rip = 0x7f3662e5d4e7 in __strncmp_sse42; saved rip = 0x7f35f64f5d6d
 called by frame at 0x7f35f4413cc0, caller of frame at 0x7f35f4413b68
 Arglist at 0x7f35f4413b60, args:
 Locals at 0x7f35f4413b60, Previous frame's sp is 0x7f35f4413b70
 Saved registers:
  rip at 0x7f35f4413b68

有没有办法检查传递给这个函数的参数？任何解释都将帮助我了解正在发生的事情。

提前感谢您的帮助。

Answer 1

跟踪传递给系统调用的参数的一种方法是使用 ltrace。并不总是保证有帮助，但尝试起来又快又轻松。下面是使用 ltrace 跟踪通过特定调用 grep 命令进行的调用的示例:

$ ltrace -s 200   grep XYZ hello.cc  2>&1 | grep XYZ
memcpy(0xe7f030, "XYZ\0", 4)                     = 0xe7f030
memchr("XYZ", '\n', 3)                           = nil
memcpy(0xe7f6b0, "XYZ", 3)                       = 0xe7f6b0
strlen("XYZ")                                    = 3
strncmp("Y", "XYZ", 3)                           = 1
strncmp("XYZ", "Y", 1)                           = -1
strlen("XYZ")                                    = 3
strcmp("XYZ", "XYZ")                             = 0
strlen("XYZ")                                    = 3
memcpy(0xe7f630, "XYZ\0", 4)                     = 0xe7f630
strlen("XYZ")                                    = 3
memcpy(0xe7f840, "XYZ", 3)                       = 0xe7f840