Re: [PATCH v11 04/10] gdb: Skip trampoline frames for the backtrace command.

[Tom Tromey <tom@tromey.com>]

>>>>> Abdul Basit Ijaz <abdul.b.ijaz@intel.com> writes:

> This change filters trampoline functions when the option
> 'skip-trampoline-functions' is set to 'on' for the backtrace command.
> Before the change, GDB prints the frames indicated by the compiler with
> DIE "DW_AT_trampoline" in the backtrace, but for better user experience,
> all such frames can be hidden from the user.

> For O2 optimized code where inlined trampoline wrappers are inlined into
> regular functions.  Check the frame's function directly for inline frames
> instead of looking up by PC, which would incorrectly return the caller's
> function.

> The test 'gdb.fortran/mixed-lang-stack' test used to fail for the IFX
> compiler because of extra trampoline frames in the backtrace.  After the
> commit, those trampoline frames are filtered and test is updated accordingly.

It's maybe somewhat unfortunate that this doesn't follow the precedent
set by Python frame filters, where a frame can be marked "elided" and
then is either printed indented (the default) or hidden (with "bt
-hide").

> diff --git a/gdb/stack.c b/gdb/stack.c
> index f41f818cebb..fa217ae9f6f 100644
> --- a/gdb/stack.c
> +++ b/gdb/stack.c
> @@ -1978,6 +1978,14 @@ backtrace_command_1 (const frame_print_options &fp_opts,
>  	{
>  	  QUIT;
 
> +	  if (skip_trampoline_functions && in_trampoline_frame (fi))
> +	    {
> +	      /* Trampoline frames are not printed so they are not counted in
> +		 the backtrace limit.  */
> +	      count++;
> +	      continue;
> +	    }

What happens if I "break 0x..." using an address in a trampoline
function and then "bt" from there?

I think this means the frame won't be printed.  But this could be
confusing because gdb will be lying about the PC.

In this scenario what would "disassemble" by itself show?

That is, I somewhat suspect that there should be a special case here for
the "live" frame.

Tom