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

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

> -----Original Message-----
> From: Schimpe, Christina
> Sent: Friday, September 26, 2025 9:45 AM
> To: 'Simon Marchi' <simark@simark.ca>; Eli Zaretskii <eliz@gnu.org>
> Cc: gdb-patches@sourceware.org; thiago.bauermann@linaro.org
> Subject: RE: [PATCH 6/9] gdb: Implement 'bt shadow' to print the shadow
> stack backtrace.
> 
> Hi Simon,
> 
> Thank you for the feedback.
> 
> > -----Original Message-----
> > From: Simon Marchi <simark@simark.ca>
> > Sent: Thursday, September 25, 2025 4:59 PM
> > To: Eli Zaretskii <eliz@gnu.org>; Schimpe, Christina
> > <christina.schimpe@intel.com>
> > Cc: gdb-patches@sourceware.org; thiago.bauermann@linaro.org
> > Subject: Re: [PATCH 6/9] gdb: Implement 'bt shadow' to print the
> > shadow stack backtrace.
> >
> > On 9/25/25 9:19 AM, Eli Zaretskii wrote:
> > >> From: "Schimpe, Christina" <christina.schimpe@intel.com>
> > >> CC: "gdb-patches@sourceware.org" <gdb-patches@sourceware.org>,
> > >> "Thiago Jung  Bauermann" <thiago.bauermann@linaro.org>
> > >> Date: Thu, 25 Sep 2025 11:06:32 +0000
> > >>
> > >>>> (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.
> > >
> > > That's what I'm saying, yes.
> > >
> > >>> 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.
> > >
> > > OK, if that's what the others want...
> >
> > My initial reaction was: why not use a "-shadow" option to the
> > backtrace command, instead of introducing "backtrace shadow", which is
> > effectively a separate command?  I then re-read the thread above, and
> > I saw that "- shadow" was actually part of the options considered, and
> > even seemed like the preferred option of many.  I didn't see "backtrace
> shadow"
> > proposed there, so I'm confused.
> 
> That's true. It has never been discussed.  When discussing this in the thread
> I didn't have the option of subcommands in mind.
> 
> > The thing I don't like about "backtrace shadow" is: I don't like when
> > a command ("backtrace") is both a prefix and a regular command.  It
> > can paint us in a corner at some point.  Let's say we want to
> > introduce the
> > syntax:
> >
> >   (gdb) backtrace SYMBOL
> >
> > at some point, then the sub-command "shadow" would conflict if
> someone
> > wanted to call the command "backtrace" with the symbol "shadow".
> 
> Good point, I did not think about that.
> 
> > From what I read in the thread above, the downside of the "backtrace -
> > shadow" option is that some other options wouldn't make sense for the
> > shadow backtrace.  I don't think it's a problem, those other options
> > can just be ignored when printing the shadow stack.
> 
> Yeah, this was one reason for me to not use "bt -shadow".
> Another reason was that the current options of the ordinary backtrace
> command only change the output format/range. The output of "bt shadow"
> looks similar in the first place, but is created completely different so I also
> wanted to make a difference by choosing the subcommand.
> 
> When moving to the implementation phase,  I decided to simply try it
> without reopening the discussion in the gdb archives again.
> But if the common opinion here is to use "bt -shadow" I have no problem in
> changing that.
> It should be straight forward to implement.

Kindly pinging for feedback on this discussion to clarify if we should better use
- "bt -shadow" (command line option) 
- "bt shadow" (subcommand approach, current implementation).

My personal opinion is still to use the subcommand approach, but, as I already said,
I think "bt -shadow" would be fine, too.

Please also see this discussion with Thiago:
https://sourceware.org/pipermail/gdb-patches/2025-October/221660.html

Kind Regards,
Christina
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