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

[Thiago Jung Bauermann <thiago.bauermann@linaro.org>]

Hello,

"Schimpe, Christina" <christina.schimpe@intel.com> writes:

>> -----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]
>> 
>> 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.

Yes, I plan to add two commands for AArch64 Guarded Control Stack, as
mentioned in that thread:

https://inbox.sourceware.org/gdb/87h6kbfazh.fsf@linaro.org/

In that email, I suggested putting them under "info shadow-stack", but
later the people in the thread considered that just adding a top-level
"shadow-stack" command would be better.

I do think that "backtrace -shadow" is a good option, so IMO we could
have both it and the "shadow-stack" umbrella command. It could even have
"shadow-stack backtrace" as an alias to "backtrace -shadow" to improve
discoverability.

You mentioned that x86 doesn't need the "enabled" and "locked" commands
because for that architecture the user can look in /proc/$PID/status,
but with those commands I also plan to allow the user to change the
enabled and locked GCS features. Wouldn't that be useful for x86?

-- 
Thiago