gdb Commands List - the first time a breakpoint is hit, commands aren't invoked

Question

When I run a program with gdb and have a commands list, the commands aren't invoked the first time the breakpoint is hit. I setup a little test program to demonstrate.

test.c:

#include <stdio.h>
void incrementI(){
     static int i = 0;
     i++;
     printf("i: %d\n", i);
     sleep(10);
}
int main() {
     int i = 0;
     while(1){
         incrementI();
     }
     return 0;
}

commands list: testgdbBreakpoint

set breakpoint pending on
b incrementI
commands
backtrace
continue
end

shell script which runs gdb: testgdbinvoke.sh

#!/bin/sh
gdb -x testGDBBreakpoint -ex=r --args testGDB

The output I see when running testgdbinvoke.sh is:

GNU gdb (GDB) 7.12.1
Copyright (C) 2017 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from testGDB...done.
Breakpoint 1 at 0x10478
Starting program: /data/config/testGDB

Breakpoint 1, 0x00010478 in incrementI ()
(gdb) c
Continuing.
i: 1

Breakpoint 1, 0x00010478 in incrementI ()
#0  0x00010478 in incrementI ()
#1  0x000104d8 in main ()
i: 2

Breakpoint 1, 0x00010478 in incrementI ()
#0  0x00010478 in incrementI ()
#1  0x000104d8 in main ()
i: 3

The first time the break point is hit, I don't see a backtrace, instead I have to manually continue. Are there specific options I have to set in the commands list in order to have them run everytime the breakpoint is hit?

Employed Russian Employed Russian · Accepted Answer · 2020-11-03T03:35:33

Reproduced using GDB-10.0.

There appears to be some kind of unexpected interaction between using multiple -x or -ex arguments. This doesn't work:
gdb -x testgdbBreakpoint -ex run ./a.out
gdb -ex 'source testgdbBreakpoint' -ex run ./a.out

But adding run at the end of testgdbBreakpoint works as expected:

gdb -q -x 'testgdbBreakpoint' ./a.out

Breakpoint 1 at 0x401136: file test.c, line 4.

Breakpoint 1, incrementI () at test.c:4
4            i++;
#0  incrementI () at test.c:4
#1  0x0000000000401189 in main () at test.c:11
i: 1

Breakpoint 1, incrementI () at test.c:4
4            i++;
#0  incrementI () at test.c:4
#1  0x0000000000401189 in main () at test.c:11
i: 2
^C

gdb Commands List - the first time a breakpoint is hit, commands aren't invoked

1 Answers