How to 'tag' a location in a C source file for a later breakpoint definition?-CodePudding

Problem: I want to be able to put different potentially unique or repeated "tags" across my C code, such that I can use them in gdb to create breakpoints.

Similar Work:

Breakpoints to line-numbers: The main difference with breakpoints on source lines, is that if the code previous to the tag is modified in such a way that it results in more or less lines, a reference to the tag would still be semantically correct, a reference to the source line would not.
Labels: I am coming from my previous question, How to tell gcc to keep my unused labels?, in which I preconceived the idea that the answer was to insert labels. Upon discussion with knowledgeable members of the platform, I was taught that label's names are not preserved after compilation. Labels not used within C are removed by the compiler.
Injecting asm labels: Related to the previous approach, if I inject asm code in the C source, certain problems arise, due to inline functions, compiler optimizations, and lack of scoping. This makes this approach not robust.
Define a dummy function: On this other question, Set GDB breakpoint in C file, there is an interesting approach, in which a "dummy" function can be placed in the code, and then add a breakpoint to the function call. The problem with this approach is that the definition of such function must be replicated for each different tag.

Is there a better solution to accomplish this? Or a different angle to attack the presented problem?

CodePudding user response：

You could create a dummy variable and set it to different values. Then you can use conditional watchpoints. Example:

#include <stdio.h>
static volatile int loc;
int main()
{
    loc = 1;
    puts("hello world");
    loc = 2;
    return 0;
}

(gdb) watch loc if loc == 2
Hardware watchpoint 1: loc
(gdb) r
Starting program: /tmp/a.out 
hello world

Hardware watchpoint 1: loc

Old value = 1
New value = 2
main () at test.c:8
8       return 0;

You can of course wrap the assignment in a macro so you only get it in debug builds. Usual caveats apply: optimizations and inlining may be affected.

CodePudding user response：

You could insert a #warning at each line where you want a breakpoint, then have a script to parse the file and line numbers from the compiler messages and write a .gdbinit file placing breakpoints at those locations.