Re: [PATCH] GDB: aarch64: Fix inferior function call if GCS is present but disabled

Hi Thiago. Thanks for the patch.

On 08/07/2026 07:03, Thiago Jung Bauermann wrote:
> On AArch64, even if the Guarded Control Stack feature is present on the
> system the inferior may not have enabled it.
> 
> There's a bug in GDB's GCS support in that if the system supports GCS,
> GDB will always push a GCS entry when doing an inferior function call
> even if the inferior doesn't have it enabled.  This causes inferior
> function calls to fail. E.g.:
> 
>    (gdb) p foo ()
>    Can't write to Guarded Control Stack.
> 
> The error message is because the GCSPR doesn't point to a valid memory
> address.
> 
> Fix by checking whether GCS is enabled in the inferior before trying to
> push a GCS entry.
> 
> Regression tested on an aarch64-linux-gnu QEMU VM with GCS present.
> ---
> 
> GCS support first appeared in GDB 17, so if this patch is approved for
> trunk is it ok to also commit it to the branch?

Sounds good to me.

> 
>   gdb/aarch64-tdep.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
> index 886e7ce1e7b6..b4437dcccc8a 100644
> --- a/gdb/aarch64-tdep.c
> +++ b/gdb/aarch64-tdep.c
> @@ -1934,7 +1934,11 @@ static void
>   aarch64_shadow_stack_push (gdbarch *gdbarch, CORE_ADDR new_addr,
>   			   regcache *regcache)
>   {
> -  aarch64_push_gcs_entry (regcache, new_addr);
> +  bool gcs_is_enabled;
> +
> +  gdbarch_get_shadow_stack_pointer (gdbarch, regcache, gcs_is_enabled);
> +  if (gcs_is_enabled)
> +    aarch64_push_gcs_entry (regcache, new_addr);
>   }
>   
>   /* Implement the "push_dummy_call" gdbarch method.  */

LGTM, with Baris' suggestion.

Approved-By: Luis Machado <[email protected]>