Hi All,
I'm looking for permission to backport this patch to the GCC-8 branch
to fix PR86486.
OK for backport?
Thanks,
Tamar
> -----Original Message-----
> From: James Greenhalgh <james.greenha...@arm.com>
> Sent: Tuesday, September 11, 2018 16:56
> To: Tamar Christina <tamar.christ...@arm.com>
> Cc: Richard Sandiford <richard.sandif...@arm.com>; Jeff Law
> <l...@redhat.com>; gcc-patches@gcc.gnu.org; nd <n...@arm.com>; Richard
> Earnshaw <richard.earns...@arm.com>; Marcus Shawcroft
> <marcus.shawcr...@arm.com>
> Subject: Re: [PATCH][GCC][AArch64] Updated stack-clash implementation
> supporting 64k probes. [patch (1/7)]
>
> On Fri, Sep 07, 2018 at 11:03:28AM -0500, Tamar Christina wrote:
> > Hi Richard,
> >
> > The 08/28/2018 21:58, Richard Sandiford wrote:
> > > Tamar Christina <tamar.christ...@arm.com> writes:
> > > > + HOST_WIDE_INT guard_used_by_caller =
> STACK_CLASH_CALLER_GUARD;
> > > > + /* When doing the final adjustment for the outgoing argument size
> we can't
> > > > + assume that LR was saved at position 0. So subtract it's offset
> > > > from
> the
> > > > + ABI safe buffer so that we don't accidentally allow an adjustment
> that
> > > > + would result in an allocation larger than the ABI buffer without
> > > > + probing. */
> > > > + HOST_WIDE_INT min_probe_threshold
> > > > + = final_adjustment_p
> > > > + ? guard_used_by_caller - cfun->machine-
> >frame.reg_offset[LR_REGNUM]
> > > > + : guard_size - guard_used_by_caller;
> > > [...]
> > > > + if (residual)
> > > > + {
> > > > + aarch64_sub_sp (temp1, temp2, residual, frame_related_p);
> > > > + if (residual >= min_probe_threshold)
> > > > + {
> > > > + if (dump_file)
> > > > + fprintf (dump_file,
> > > > + "Stack clash AArch64 prologue residuals: "
> > > > + HOST_WIDE_INT_PRINT_DEC " bytes, probing will be
> required."
> > > > + "\n", residual);
> > > > + emit_stack_probe (plus_constant (Pmode, stack_pointer_rtx,
> > > > + STACK_CLASH_CALLER_GUARD));
> > >
> > > reg_offsets are nonnegative, so if LR_REGNUM isn't saved at position
> > > 0, min_probe_threshold will be less than STACK_CLASH_CALLER_GUARD.
> > > It looks like the probe would then write above the region.
> > >
> > > Using >= rather than > means that the same thing could happen when
> > > LR_REGNUM is at position 0, if the residual is exactly
> > > STACK_CLASH_CALLER_GUARD.
> >
> > That's true. While addressing this we changed how the residuals are
> probed.
> >
> > To address a comment you raised offline about the saving of LR when
> > calling a no-return function using a tail call and
> > -fomit-frame-pointer, I think this should be safe as the code in
> frame_layout (line 4131-4136) would ensure that R30 is saved.
> >
> > I have added two new tests to check for this, so that if it does
> > change in the future they would fail.
> >
> > Attached is the updated patch and new changelog
> >
> > Ok for trunk?
>
> I'm happy with this patch version; I'd have preferred a FORNOW comment on
> this:
>
> > + /* If SIZE is not large enough to require probing, just adjust the stack
> > and
> > + exit. */
> > + if (!poly_size.is_constant (&size)
> > + || known_lt (poly_size, min_probe_threshold)
> > + || !flag_stack_clash_protection)
>
> as you don't fix it until 2/7, but that is a minor point.
>
> I'm happy with you responding to Richard S' request for an assert either in
> this patch, or tacked on as an 8/7.
>
> OK.
>
> Thanks,
> James
>
> > Thanks,
> > Tamar
> >
> > gcc/
> > 2018-09-07 Jeff Law <l...@redhat.com>
> > Richard Sandiford <richard.sandif...@linaro.org>
> > Tamar Christina <tamar.christ...@arm.com>
> >
> > PR target/86486
> > * config/aarch64/aarch64.md
> > (probe_stack_range): Add k (SP) constraint.
> > * config/aarch64/aarch64.h (STACK_CLASH_CALLER_GUARD,
> > STACK_CLASH_MAX_UNROLL_PAGES): New.
> > * config/aarch64/aarch64.c (aarch64_output_probe_stack_range):
> Emit
> > stack probes for stack clash.
> > (aarch64_allocate_and_probe_stack_space): New.
> > (aarch64_expand_prologue): Use it.
> > (aarch64_expand_epilogue): Likewise and update IP regs re-use
> criteria.
> > (aarch64_sub_sp): Add emit_move_imm optional param.
> >
> > gcc/testsuite/
> > 2018-09-07 Jeff Law <l...@redhat.com>
> > Richard Sandiford <richard.sandif...@linaro.org>
> > Tamar Christina <tamar.christ...@arm.com>
> >
> > PR target/86486
> > * gcc.target/aarch64/stack-check-12.c: New.
> > * gcc.target/aarch64/stack-check-13.c: New.
> > * gcc.target/aarch64/stack-check-cfa-1.c: New.
> > * gcc.target/aarch64/stack-check-cfa-2.c: New.
> > * gcc.target/aarch64/stack-check-prologue-1.c: New.
> > * gcc.target/aarch64/stack-check-prologue-10.c: New.
> > * gcc.target/aarch64/stack-check-prologue-11.c: New.
> > * gcc.target/aarch64/stack-check-prologue-12.c: New.
> > * gcc.target/aarch64/stack-check-prologue-13.c: New.
> > * gcc.target/aarch64/stack-check-prologue-14.c: New.
> > * gcc.target/aarch64/stack-check-prologue-15.c: New.
> > * gcc.target/aarch64/stack-check-prologue-2.c: New.
> > * gcc.target/aarch64/stack-check-prologue-3.c: New.
> > * gcc.target/aarch64/stack-check-prologue-4.c: New.
> > * gcc.target/aarch64/stack-check-prologue-5.c: New.
> > * gcc.target/aarch64/stack-check-prologue-6.c: New.
> > * gcc.target/aarch64/stack-check-prologue-7.c: New.
> > * gcc.target/aarch64/stack-check-prologue-8.c: New.
> > * gcc.target/aarch64/stack-check-prologue-9.c: New.
> > * gcc.target/aarch64/stack-check-prologue.h: New.
> > * lib/target-supports.exp
> > (check_effective_target_supports_stack_clash_protection): Add
> AArch64.
> >
