CODEWITHSUNDEEP
gdbbreakpoints
Celelibi
Celelibi

Reputation: 1501

gdb: A "continue" that doesn't interfer with "next" or "step"

I'm currently debugging syslinux (a boot loader) through the gdb stub of qemu.

Recently, I wrote some gdb commands that (un)load the debug symbols everytime a module is dynamically (un)loaded. In order not to disrupt the execution, I ended the commands with continue.

break com32/lib/sys/module/elf_module.c:282
commands
    silent
    python
name = gdb.parse_and_eval("module->name").string()
addr = int(str(gdb.parse_and_eval("module->base_addr")), 0)
gdb.execute("load-syslinux-module %s 0x%08x" % (name, addr))
    end
    continue
end

However, when stepping through the code line by line, if the next or step command makes the execution hit the breakpoint, the breakpoints takes precedence, the commands are executed, including the continue. And the execution continue irrespectively of the line-by-line debugging I was doign. This also happen if I try to step over the function that has this breakpoint.

How can I keep (un)loading the debug symbols on the fly while not interfering with the debugging?

Is there an alternative to the continue command? Maybe using breakpoints isn't the right way? I'd take any solution.

Upvotes: 1

Views: 849

Answers (1)

Tom Tromey
Tom Tromey

Reputation: 22539

This can't be done from the gdb CLI. However, it is easy to do from Python.

In Python the simplest way is to define one's own gdb.Breakpoint subclass, and define the stop method on it. This method can do the work you like, then return False to tell gdb to continue.

The stop facility was designed to avoid the problems with cont in commands. See the documentation for more details.

Upvotes: 2

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