The 10/13/2023 11:29, Richard Earnshaw (lists) wrote:
> On 05/09/2023 16:00, Richard Sandiford via Gcc-patches wrote:
> > Szabolcs Nagy <szabolcs.n...@arm.com> writes:
> >> @@ -4,19 +4,19 @@ void __attribute__ ((target("branch-protection=leaf")))
> >> foo1 ()
> >> {
> >> }
> >> -/* { dg-error {invalid protection type 'leaf' in
> >> 'target\("branch-protection="\)' pragma or attribute} "" { target *-*-* }
> >> 5 } */
> >> +/* { dg-error {invalid argument 'leaf' for
> >> 'target\("branch-protection="\)'} "" { target *-*-* } 5 } */
> >> /* { dg-error {pragma or attribute 'target\("branch-protection=leaf"\)'
> >> is not valid} "" { target *-*-* } 5 } */
>
> 'leaf' is really a modifier for the other branch protection strategies;
> perhaps it would be better to describe it as that.
this error message is used for arbitrary strings, e.g.
branch-protection=foobar or branch-protection=bti+foo.
with further processing we can figure out that 'leaf'
is a valid modifier for pac-ret and change the error to
invalid placement of modifier 'leaf' in 'target("branch-protection=")'
otherwise fall back to
invalid argument 'foobar' for 'target("branch-protection=")'.
does that help?
(currently 'leaf' and 'b-key' are the only modifiers.)
> But this brings up another issue/question. If the compiler has been
> configured with, say, '--enable-branch-protection=standard' or some other
> variety, is there (or do we want) a way to extend that to leaf functions
> without changing the underlying strategy?
there are several limitations in branch-protection handling,
i'm only fixing bugs and assumptions that don't work when arm
and aarch64 has different set of branch-protection options.
i think it can be useful to add/remove branch-protection options
incrementally in cflags instead of having one string, but it's
not obvious to me how to get there.
> >> void __attribute__ ((target("branch-protection=none+pac-ret")))
> >> foo2 ()
> >> {
> >> }
> >> -/* { dg-error "unexpected 'pac-ret' after 'none'" "" { target *-*-* } 12
> >> } */
> >> +/* { dg-error {argument 'none' can only appear alone in
> >> 'target\("branch-protection="\)'} "" { target *-*-* } 12 } */
>
> Or maybe better still: "branch protection strategies 'none' and 'pac-ret' are
> incompatible".
i can make this change, but e.g.
in case of branch-protection=standard+bti+foo it would
say "'standard' and 'bti' are incompatible" which can be
surprising given that standard includes bti, meanwhile
"'standard' can only appear alone" explains the problem.
> But this is all a matter of taste.
>
> However, this patch should be merged with the patch that changes the error
> messages. Or has that already gone in?
i can do that merge.
