Re: [PATCH 7/9] gdb: Provide gdbarch hook to distinguish shadow stack backtrace elements.

[Eli Zaretskii <eliz@gnu.org>]

> From: Christina Schimpe <christina.schimpe@intel.com>
> Date: Tue, 23 Sep 2025 11:18:40 +0000
> 
> On x86 with CET there can be elements on the shadow stack which are not
> return addresses.  In this case, we just want to print the element itself
> in the shadow stack backtrace, but no further information.
> 
> Provide a gdbarch hook to distinguish between return and non-return
> addresses and use it to print the shadow stack backtrace as described
> above.
> ---
>  gdb/doc/gdb.texinfo       | 19 ++++++++++++
>  gdb/gdbarch-gen.c         | 32 ++++++++++++++++++++
>  gdb/gdbarch-gen.h         | 15 +++++++++
>  gdb/gdbarch.h             |  1 +
>  gdb/gdbarch_components.py | 17 +++++++++++
>  gdb/shadow-stack.c        | 64 +++++++++++++++++----------------------
>  gdb/shadow-stack.h        | 37 ++++++++++++++++++++++
>  7 files changed, 148 insertions(+), 37 deletions(-)

Thanks.

> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index ebda4546b58..a0fde385a8e 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -8887,6 +8887,25 @@ This is how a shadow stack backtrace looks like on amd64:
>  @end group
>  @end smallexample
>  
> +There can be elements on the shadow stack which are not return addresses,
> +for example on x86 with the Intel Control-Flow Enforcement Technology
> +(@xref{CET}).  In case of signals, the old shadow stack pointer is pushed
               ^
A cross-reference is missing here.

> +in a special format with bit 63 set.  For such shadow stack elements, the
> +shadow stack frame just contains the level and the address on the shadow
> +stack, as shown in the following example by frame 1:
> +
> +@smallexample
> +@group
> +(gdb) bt shadow 4
> +#0  0x00007ffff7c54d90 in __restore_rt from /lib64/libc.so.6
> +#1  0x80007ffff79fffd8
> +#2  0x00007ffff7c54ce6 in __GI_raise at ../sysdeps/posix/raise.c:27
> +#3  0x000000000040115d in main at /tmp/amd64-shadow-stack-signal.c:32
> +(More shadow stack frames follow...)
> +@end group
> +@end smallexample

Would it make sense to show something like "<signal caught>", instead
of a frame with only an address?

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