Re: [PATCH 1/2] Allow debugging of runtime loader / dynamic linker

[Lancelot SIX <lsix@lancelotsix.com>]

Hi Kevin,

We have recently encountered a bug with the master branch.  Simon have
opened https://sourceware.org/bugzilla/show_bug.cgi?id=29747 to track
it.

By running `git bisect`, it seems that this problem appeared with this
patch.

Do you think you would have time to investigate this issue?  I have not
looked at the actual problem yet.  I have just been looking at when the
regression got introduced.

I do not expect it to be too long to fix, but I am not familiar with
this part of the code.

Please let me know if you do not have time to investigate this.

Best,
Lancelot.

On Fri, Oct 07, 2022 at 08:57:15PM -0700, Kevin Buettner via Gdb-patches wrote:
> At present, GDB does not allow for the debugging of the runtime loader
> and/or dynamic linker.  Much of the time, this makes sense.  An
> application programmer doesn't normally want to see symbol resolution
> code when stepping into a function that hasn't been resolved yet.
> 
> But someone who wishes to debug the runtime loader / dynamic linker
> might place a breakpoint in that code and then wish to debug it
> as normal.  At the moment, this is not possible.  Attempting to step
> will cause GDB to internally step (and not stop) until code
> unrelated to the dynamic linker is reached.
> 
> This commit makes a minor change to infrun.c which allows the dynamic
> loader / linker to be debugged in the case where a step, next, etc.
> is initiated from within that code.
> 
> While developing this fix, I tried some approaches which weren't quite
> right.  The GDB testusite definitely contains tests which FAIL when
> it's done incorrectly.  (At one point, I saw 17 regressions!) This
> commit has been tested on x86-64 linux with no regressions.
> ---
>  gdb/infrun.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 1957e8020dd..52441b7ab5c 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -6961,7 +6961,10 @@ process_event_stop_test (struct execution_control_state *ecs)
>  
>    if (execution_direction != EXEC_REVERSE
>        && ecs->event_thread->control.step_over_calls == STEP_OVER_UNDEBUGGABLE
> -      && in_solib_dynsym_resolve_code (ecs->event_thread->stop_pc ()))
> +      && in_solib_dynsym_resolve_code (ecs->event_thread->stop_pc ())
> +      && !in_solib_dynsym_resolve_code (
> +	  ecs->event_thread->control.step_start_function->value_block ()
> +	      ->entry_pc ()))
>      {
>        CORE_ADDR pc_after_resolver =
>  	gdbarch_skip_solib_resolver (gdbarch, ecs->event_thread->stop_pc ());
> -- 
> 2.37.3
>