c – gdb |查看变量参数列表

我使用bt命令查看堆栈跟踪.输出是

(gdb) bt
#0  0x001ae4cd in Debugger (message=0x1 "???\a") at /SourceCache/xnu/xnu-1228.7.58/osfmk/i386/AT386/model_dep.c:705
#1  0x3bf97000 in ?? ()
#2  0x0012b0fa in panic (str=0x5ef "") at /SourceCache/xnu/xnu-1228.7.58/osfmk/kern/debug.c:274
#3  0x001a8cd4 in kernel_trap (state=0x51a67c80) at /SourceCache/xnu/xnu-1228.7.58/osfmk/i386/trap.c:680
#4  0x0019ede5 in return_from_trap () at pmap.h:176
#5  0x00132bea in __doprnt (fmt=<value temporarily unavailable,due to optimizations>,argp=0x51a67e6c,putc=0x38ad24 <kvprintf+33>,arg=0x51a67e48,radix=10) at /SourceCache/xnu/xnu-1228.7.58/osfmk/kern/printf.c:439
#6  0x0038ad11 in kvprintf (fmt=0x1 "???\a",func=0x1,arg=0x1,radix=1,ap=0x51a67e84 "\\?\034I\"") at /SourceCache/xnu/xnu-1228.7.58/bsd/kern/subr_prf.c:525
#7  0x491b5dac in com_my_drv_Log (format=0x491cbff8 "%s::%s:%n\n") at Logger.cpp:37
#8  0x491b3d36 in MyDrv::init (this=0x5c1f200,properties=0x58a8040) at MyDrv.cpp:34
#9  0x00412887 in IOService::probeCandidates (this=0x599a980,matches=0x58ade80) at /SourceCache/xnu/xnu-1228.7.58/iokit/Kernel/IOService.cpp:2512
#10 0x004124ab in IOService::doServiceMatch (this=0x534180,options=8) at /SourceCache/xnu/xnu-1228.7.58/iokit/Kernel/IOService.cpp:2921
#11 0x00411127 in _IOConfigThread::main (self=0x58c6790) at /SourceCache/xnu/xnu-1228.7.58/iokit/Kernel/IOService.cpp:3125
(gdb)

在框架

#7  0x491b5dac in com_my_drv_Log

我如何查看通过签名传递给我的com_my_drv_Log的参数

void com_my_drv_Log (const char* format,...);
/* with the variable argument list */

？

解决方法

看起来像这样可以做一个简单的程序：

#include <stdarg.h>
#include <stdio.h>

void myfunc(const char *fmt,...)
{
        va_list args;
        va_start(args,fmt);
        vprintf(fmt,args);
        va_end(args);
        return;
}

int main(int argc,char *argv[])
{
        myfunc("test 1: %s %s\n","one","two");
        myfunc("test 2: %s %d %c\n","apple",222,'y');
        return 0;
}

这是gdb会话示例：

$gdb testprog
GNU gdb (GDB) 7.1-debian
[snip]
Reading symbols from /home/user/testprog...done.
(gdb) break myfunc
Breakpoint 1 at 0x400552: file testprog.c,line 7.
(gdb) run
Starting program: /home/user/testprog

Breakpoint 1,myfunc (fmt=0x4006f4 "test 1: %s %s\n") at testprog.c:7
7               va_start(args,fmt);
(gdb) # initialize args to hold correct values:
(gdb) step
8               vprintf(fmt,args);
(gdb) # print first argument in "..." list which we kNow is a char*:
(gdb) p *(char **)(((char *)args[0].reg_save_area)+args[0].gp_offset)
$1 = 0x4006f0 "one"

我没有测试所有这一切,看这个link完整的解决方案. This blog也将有用.

原文地址：https://www.jb51.cc/c/114972.html