RE: [PATCH 6/9] gdb: Implement 'bt shadow' to print the shadow stack backtrace.

["Schimpe, Christina" <christina.schimpe@intel.com>]

Hi Eli, 

Thanks for the quick feedback! Please find my comments below.

> -----Original Message-----
> From: Eli Zaretskii <eliz@gnu.org>
> Sent: Tuesday, September 23, 2025 1:47 PM
> To: Schimpe, Christina <christina.schimpe@intel.com>
> Cc: gdb-patches@sourceware.org
> Subject: Re: [PATCH 6/9] gdb: Implement 'bt shadow' to print the shadow
> stack backtrace.
> 
> > From: Christina Schimpe <christina.schimpe@intel.com>
> > Date: Tue, 23 Sep 2025 11:18:39 +0000
> >
> > Add a subcommand 'bt shadow' for the ordinary backtrace command which
> > prints the shadow stack backtrace.
> > Similar to the ordinary backtrace command 'bt shadow' can be
> > configured using COUNT and the command line option -frame-info.
> > However, we always print the address and the command is not affected
> > by the setting "print address" as well as the setting "print frame-info
> location-and-address".
> > Also we do not print the frame arguments.
> >
> > Usage: backtrace|bt shadow [OPTION]... [COUNT | -COUNT]
> >
> > Help output:
> > ~~
> > (gdb) help bt shadow
> > Print backtrace of all shadow stack frames, or innermost COUNT frames.
> > Usage: backtrace shadow [OPTION]... [COUNT | -COUNT]
> 
> Thanks, but I wonder if this UI is the best we can come up with.
> The "backtrace" command doesn't currently have non-option arguments
> except COUNT. 

Hm, not sure if I fully understand what you mean by non-option arguments.
"bt shadow" does not introduce more non-option arguments, except if you say
that "shadow" itself is interpreted as "non-option" argument.

> We have just got rid of qualifier arguments like "full"
> and "hide".  Instead of introducing qualifier arguments anew, why not go the
> way of thread-related commands and add a new command "shadow", so the
> user could say "shadow backtrace" and maybe in the future also other sub-
> commands?

This has been discussed in a thread years ago:
https://sourceware.org/pipermail/gdb/2023-December/051024.html
The direction was to make it part of the ordinary bt command. 

Currently, we don't plan any further commands for the shadow stack. But
maybe for ARM's Guarded Control Stack any further options are planned?
I added Thiago in cc here. Maybe he has some more input.

> Also, a question: can I say something like "thread apply 1-10 bt shadow"?

Yes, this is possible:
~~~
(gdb) thread apply all bt shadow

Thread 2.1 (Thread 0x7ffff7fae740 (LWP 403202) "sample"):
#0  0x00007ffff7c2a1ca in __libc_start_call_main at ../sysdeps/nptl/libc_start_call_main.h:74
#1  0x00007ffff7c2a28b in __libc_start_main_impl at ../csu/libc-start.c:128
#2  0x0000555555555065 in _start

Thread 1.1 (Thread 0x7ffff7fae740 (LWP 403193) "sample"):
#0  0x00007ffff7c2a1ca in __libc_start_call_main at ../sysdeps/nptl/libc_start_call_main.h:74
#1  0x00007ffff7c2a28b in __libc_start_main_impl at ../csu/libc-start.c:128
#2  0x0000555555555065 in _start
~~~

> > +* New commands
> > +
> > +backtrace shadow [option]... [count | -count] bt shadow [option]...
> > +[count | -count]
> > +  Print backtrace of all shadow stack frames, or innermost 'count' frames.
> > +  The command is a subcommand of the ordinary backtrace command.
> > +
> >  *** Changes in GDB 17
> 
> This part is okay (subject to the general comment above).
> 
> > +This is how a shadow stack backtrace looks like on amd64:
> > +@smallexample
> > +@group
> > +#0  0x000000000040111f in call1 at amd64-shadow-stack.c:14
> > +#1  0x000000000040112f in main at amd64-shadow-stack.c:21
> > +#2  0x00007ffff7c3fe70 in __libc_start_call_main at
> > +../sysdeps/nptl/libc_start_call_main.h:58
> 
> This line is too long.  Since this is just an example, I suggest to make it artificially
> shorter by editing the names of the functions and file names.

I agree and will fix. 

Kind Regards
Christina

> Reviewed-By: Eli Zaretskii <eliz@gnu.org>
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