[PATCH v4 1/2] aarch64: Lock GCS status at startup

[Yury Khrustalev]

On Tue, Feb 17, 2026 at 09:49:29AM -0300, Adhemerval Zanella Netto wrote:
> 
> On 16/02/26 14:25, Yury Khrustalev wrote:
> > If GCS is enabled (see tunable glibc.cpu.aarch64_gcs), we lock all GCS
> > operations (including status, write on shadow stack, and push to shadow
> > stack) unless OPTIONAL policy is used.
> 
> Patch look ok, some minor nits below. I think we can just fix them, install
> and send a committed version.
> 
> Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Thanks!

> ...
>
> > +  uint64_t gcs = GL (dl_aarch64_gcs);
> > +  if (gcs != GCS_POLICY_DISABLED)
> >      {
> > -      int ret = INLINE_SYSCALL_CALL (prctl, PR_SET_SHADOW_STACK_STATUS,
> > -				     PR_SHADOW_STACK_ENABLE, 0, 0, 0);
> > -      if (ret)
> > -        _dl_fatal_printf ("failed to enable GCS: %d\n", -ret);
> > +      int r0 = INLINE_SYSCALL_CALL (prctl, PR_SET_SHADOW_STACK_STATUS,
> > +				    PR_SHADOW_STACK_ENABLE, 0, 0, 0);
> > +      if (r0)
> 
> No implicit checks (r0 != 0)

OK

> and I think you can just remove r0 and
> check the INLINE_SYSCALL_CALL return directly in the if.

We use returned value for error reporting, so we need a variable.