Re: [PATCH] [PR target/96350]Force ENDBR immediate into memory to avoid fake ENDBR opcode.

[Uros Bizjak <ubizjak@gmail.com>]

On Fri, Aug 14, 2020 at 6:54 AM Hongtao Liu <crazylht@gmail.com> wrote:
>
> On Tue, Aug 11, 2020 at 5:56 PM Uros Bizjak <ubizjak@gmail.com> wrote:
> >
> > On Tue, Aug 11, 2020 at 11:36 AM Hongtao Liu <crazylht@gmail.com> wrote:
> > >
> > > On Tue, Aug 11, 2020 at 4:38 PM Uros Bizjak <ubizjak@gmail.com> wrote:
> > > >
> > > > On Tue, Aug 11, 2020 at 5:30 AM Hongtao Liu <crazylht@gmail.com> wrote:
> > > > >
> > > > > Hi:
> > > > >   The issue is described in the bugzilla.
> > > > >   Bootstrap is ok, regression test for i386/x86-64 backend is ok.
> > > > >   Ok for trunk?
> > > > >
> > > > > ChangeLog
> > > > > gcc/
> > > > >         PR target/96350
> > > > >         * config/i386/i386.c (ix86_legitimate_constant_p): Return
> > > > >         false for ENDBR immediate.
> > > > >         (ix86_legitimate_address_p): Ditto.
> > > > >         * config/i386/predicated.md
> > > > >         (x86_64_immediate_operand): Exclude ENDBR immediate.
> > > > >         (x86_64_zext_immediate_operand): Ditto.
> > > > >         (x86_64_dwzext_immediate_operand): Ditto.
> > > > >         (ix86_not_endbr_immediate_operand): New predicate.
> > > > >
> > > > > gcc/testsuite
> > > > >         * gcc.target/i386/endbr_immediate.c: New test.
> > > >
> > > > +;; Return true if VALUE isn't an ENDBR opcode in immediate field.
> > > > +(define_predicate "ix86_not_endbr_immediate_operand"
> > > > +  (match_test "1")
> > > >
> > > > Please reverse the above logic to introduce
> > > > ix86_endbr_immediate_operand, that returns true for unwanted
> > > > immediate. Something like:
> > > >
> > > > (define_predicate "ix86_endbr_immediate_operand"
> > > >   (match_code "const_int")
> > > > ...
> > > >
> > > > And you will be able to use it like:
> > > >
> > > > if (ix86_endbr_immediate_operand (x, VOIDmode)
> > > >   return false;
> > > >
> > >
> > > Changed.
> >
> > No, it is not.
> >
> > +  if ((flag_cf_protection & CF_BRANCH)
> > +      && CONST_INT_P (op))
> >
> > You don't need to check for const ints here.
> >
> > And please rewrite the body of the function to something like (untested):
> >
> > {
> >   unsigned HOST_WIDE_INT val = TARGET_64BIT ? 0xfa1e0ff3 : 0xfb1e0ff3;
> >
> >   if (x == val)
> >     return 1;
> >
> >   if (TARGET_64BIT)
> >     for (; x >= val; x >>= 8)
> >       if (x == val)
> >         return 1;
> >
> >   return 0;
> > }
> >
> > so it will at least *look* like some thoughts have been spent on this.
> > I don't plan to review the code where it is obvious from the first
> > look that it was thrown together in a hurry. Please get some internal
> > company signoff first. Ping me in a week for a review.
> >
>
> Sorry for the hurry, i know your time is precious.
>
> > Uros.
> > >
> > > >    /* Otherwise we handle everything else in the move patterns.  */
> > > > -  return true;
> > > > +  return ix86_not_endbr_immediate_operand (x, VOIDmode);
> > > >  }
> > > >
> > > > Please handle this in CASE_CONST_SCALAR_INT: part.
> > > >
> > > > +  if (disp && !ix86_not_endbr_immediate_operand (disp, VOIDmode))
> > > > +    return false;
> > > >
> > > > And this in:
> > > >
> > > >   /* Validate displacement.  */
> > > >   if (disp)
> > > >     {
> > > >
> > >
> > > Changed.
> >
> > A better place for these new special cases is at the beginning of the
> > part I referred, not at the end.
> >
>
> Yes.
>
> > Uros.
>
> Update patch.

OK with two nits below.

Thanks,
Uros.

+  if (flag_cf_protection & CF_BRANCH)
+     {
+       unsigned HOST_WIDE_INT imm = INTVAL (op);

UINTVAL, just for the consistency.

+       unsigned HOST_WIDE_INT val = TARGET_64BIT ? 0xfa1e0ff3 : 0xfb1e0ff3;

@@ -374,6 +402,8 @@
 (define_predicate "x86_64_dwzext_immediate_operand"
   (match_code "const_int,const_wide_int")
 {
+  if (ix86_endbr_immediate_operand (op, VOIDmode))
+    return false;

vertical space here.
   switch (GET_CODE (op))

>
> --
> BR,
> Hongtao