GDB Debugging Skills (3)

by Bramante - - | Comments

在gdb batch mode要怎麼印出每次執行某API的return value, 方法如下.

範例程式:

test.c
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#include <stdio.h>
#include <time.h>
#include <stdlib.h>

int test(int arg)
{
 printf("@test(arg:%d)\n",arg);
 return arg ;
}

int main(int argc, char *argv[])
{
 if(argc == 2)
   {
    int num = atoi(argv[1]);
    int i ;
    for( i = 0 ; i < num ; i ++ )
       {
        test(i);
        sleep(1);
       }
   }
 return 0 ;
}

編譯與執行:

Terminal
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bramante@matrix:~/test$ gcc -g -o ./test ./test.c
bramante@matrix:~/test$ gdb --batch --command=gdb.cmds --args ./test 3
Breakpoint 1 at 0x40058f: file ./test.c, line 7.

Breakpoint 1, test (arg=0) at ./test.c:7
7        printf("@test(arg:%d)\n",arg);
arg = 0
@test(arg:0)
main (argc=2, argv=0x7fffffffe5b8) at ./test.c:20
20              sleep(1);
Value returned is $1 = 0

Breakpoint 1, test (arg=1) at ./test.c:7
7        printf("@test(arg:%d)\n",arg);
arg = 1
@test(arg:1)
main (argc=2, argv=0x7fffffffe5b8) at ./test.c:20
20              sleep(1);
Value returned is $2 = 1

Breakpoint 1, test (arg=2) at ./test.c:7
7        printf("@test(arg:%d)\n",arg);
arg = 2
@test(arg:2)
main (argc=2, argv=0x7fffffffe5b8) at ./test.c:20
20              sleep(1);
Value returned is $3 = 2
[Inferior 1 (process 2986) exited normally]
bramante@matrix:~/test$

可以看到test()被執行了3次, 它的return value都被gdb給印了出來.

前面所用到的gdb.cmds檔案的內容如下:

gdb.cmds
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b test

define printFuncInfo
  info args
  finish
  continue
end

commands 1
  printFuncInfo
end

run

要注意, gdb.cmds的內容不能寫成下面這樣, 不然commands在執行到finish後, 在finish後面的command都不會被執行, 需要寫成像前面那樣, 用個user-defined commands把這些command多包一層, 才能避開這個問題.

錯誤的gdb.cmds
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b test

commands 1
  info args
  finish
  continue
end

run

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