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.
>
