[PATCH 00/19] aarch64: Fix -fstack-protector issue

[PATCH 00/19] aarch64: Fix -fstack-protector issue

[Richard Sandiford]

This series of patches fixes deficiencies in GCC's -fstack-protector
implementation for AArch64 when using dynamically allocated stack space.
This is CVE-2023-4039.  See:

https://developer.arm.com/Arm%20Security%20Center/GCC%20Stack%20Protector%20Vulnerability%20AArch64
https://github.com/metaredteam/external-disclosures/security/advisories/GHSA-x7ch-h5rf-w2mf

for more details.

The fix is to put the saved registers above the locals area when
-fstack-protector is used.

The series also fixes a stack-clash problem that I found while working
on the CVE.  In unpatched sources, the stack-clash problem would only
trigger for unrealistic numbers of arguments (8K 64-bit arguments, or an
equivalent).  But it would be a more significant issue with the new
-fstack-protector frame layout.  It's therefore important that both
problems are fixed together.

Some reorganisation of the code seemed necessary to fix the problems in a
cleanish way.  The series is therefore quite long, but only a handful of
patches should have any effect on code generation.

See the individual patches for a detailed description.

Tested on aarch64-linux-gnu. Pushed to trunk and to all active branches.
I've also pushed backports to GCC 7+ to vendors/ARM/heads/CVE-2023-4039.

Richard Sandiford (19):
  aarch64: Use local frame vars in shrink-wrapping code
  aarch64: Avoid a use of callee_offset
  aarch64: Explicitly handle frames with no saved registers
  aarch64: Add bytes_below_saved_regs to frame info
  aarch64: Add bytes_below_hard_fp to frame info
  aarch64: Tweak aarch64_save/restore_callee_saves
  aarch64: Only calculate chain_offset if there is a chain
  aarch64: Rename locals_offset to bytes_above_locals
  aarch64: Rename hard_fp_offset to bytes_above_hard_fp
  aarch64: Tweak frame_size comment
  aarch64: Measure reg_offset from the bottom of the frame
  aarch64: Simplify top of frame allocation
  aarch64: Minor initial adjustment tweak
  aarch64: Tweak stack clash boundary condition
  aarch64: Put LR save probe in first 16 bytes
  aarch64: Simplify probe of final frame allocation
  aarch64: Explicitly record probe registers in frame info
  aarch64: Remove below_hard_fp_saved_regs_size
  aarch64: Make stack smash canary protect saved registers

 gcc/config/aarch64/aarch64.cc                 | 518 ++++++++++--------
 gcc/config/aarch64/aarch64.h                  |  44 +-
 .../aarch64/stack-check-prologue-17.c         |  55 ++
 .../aarch64/stack-check-prologue-18.c         | 100 ++++
 .../aarch64/stack-check-prologue-19.c         | 100 ++++
 .../aarch64/stack-check-prologue-20.c         |   3 +
 .../gcc.target/aarch64/stack-protector-8.c    |  95 ++++
 .../gcc.target/aarch64/stack-protector-9.c    |  33 ++
 .../aarch64/sve/pcs/stack_clash_3.c           |   6 +-
 9 files changed, 699 insertions(+), 255 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-17.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-18.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-19.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-20.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-protector-8.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-protector-9.c

-- 
2.25.1

[PATCH 01/19] aarch64: Use local frame vars in shrink-wrapping code

[Richard Sandiford]

aarch64_layout_frame uses a shorthand for referring to
cfun->machine->frame:

  aarch64_frame &frame = cfun->machine->frame;

This patch does the same for some other heavy users of the structure.
No functional change intended.

gcc/
	* config/aarch64/aarch64.cc (aarch64_save_callee_saves): Use
	a local shorthand for cfun->machine->frame.
	(aarch64_restore_callee_saves, aarch64_get_separate_components):
	(aarch64_process_components): Likewise.
	(aarch64_allocate_and_probe_stack_space): Likewise.
	(aarch64_expand_prologue, aarch64_expand_epilogue): Likewise.
	(aarch64_layout_frame): Use existing shorthand for one more case.
---
 gcc/config/aarch64/aarch64.cc | 123 ++++++++++++++++++----------------
 1 file changed, 64 insertions(+), 59 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 37d414021ca..b91f77d7b1f 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8651,7 +8651,7 @@ aarch64_layout_frame (void)
   frame.is_scs_enabled
     = (!crtl->calls_eh_return
        && sanitize_flags_p (SANITIZE_SHADOW_CALL_STACK)
-       && known_ge (cfun->machine->frame.reg_offset[LR_REGNUM], 0));
+       && known_ge (frame.reg_offset[LR_REGNUM], 0));
 
   /* When shadow call stack is enabled, the scs_pop in the epilogue will
      restore x30, and we don't need to pop x30 again in the traditional
@@ -9117,6 +9117,7 @@ aarch64_save_callee_saves (poly_int64 start_offset,
 			   unsigned start, unsigned limit, bool skip_wb,
 			   bool hard_fp_valid_p)
 {
+  aarch64_frame &frame = cfun->machine->frame;
   rtx_insn *insn;
   unsigned regno;
   unsigned regno2;
@@ -9131,8 +9132,8 @@ aarch64_save_callee_saves (poly_int64 start_offset,
       bool frame_related_p = aarch64_emit_cfi_for_reg_p (regno);
 
       if (skip_wb
-	  && (regno == cfun->machine->frame.wb_push_candidate1
-	      || regno == cfun->machine->frame.wb_push_candidate2))
+	  && (regno == frame.wb_push_candidate1
+	      || regno == frame.wb_push_candidate2))
 	continue;
 
       if (cfun->machine->reg_is_wrapped_separately[regno])
@@ -9140,7 +9141,7 @@ aarch64_save_callee_saves (poly_int64 start_offset,
 
       machine_mode mode = aarch64_reg_save_mode (regno);
       reg = gen_rtx_REG (mode, regno);
-      offset = start_offset + cfun->machine->frame.reg_offset[regno];
+      offset = start_offset + frame.reg_offset[regno];
       rtx base_rtx = stack_pointer_rtx;
       poly_int64 sp_offset = offset;
 
@@ -9153,7 +9154,7 @@ aarch64_save_callee_saves (poly_int64 start_offset,
 	{
 	  gcc_assert (known_eq (start_offset, 0));
 	  poly_int64 fp_offset
-	    = cfun->machine->frame.below_hard_fp_saved_regs_size;
+	    = frame.below_hard_fp_saved_regs_size;
 	  if (hard_fp_valid_p)
 	    base_rtx = hard_frame_pointer_rtx;
 	  else
@@ -9175,8 +9176,7 @@ aarch64_save_callee_saves (poly_int64 start_offset,
 	  && (regno2 = aarch64_next_callee_save (regno + 1, limit)) <= limit
 	  && !cfun->machine->reg_is_wrapped_separately[regno2]
 	  && known_eq (GET_MODE_SIZE (mode),
-		       cfun->machine->frame.reg_offset[regno2]
-		       - cfun->machine->frame.reg_offset[regno]))
+		       frame.reg_offset[regno2] - frame.reg_offset[regno]))
 	{
 	  rtx reg2 = gen_rtx_REG (mode, regno2);
 	  rtx mem2;
@@ -9226,6 +9226,7 @@ static void
 aarch64_restore_callee_saves (poly_int64 start_offset, unsigned start,
 			      unsigned limit, bool skip_wb, rtx *cfi_ops)
 {
+  aarch64_frame &frame = cfun->machine->frame;
   unsigned regno;
   unsigned regno2;
   poly_int64 offset;
@@ -9242,13 +9243,13 @@ aarch64_restore_callee_saves (poly_int64 start_offset, unsigned start,
       rtx reg, mem;
 
       if (skip_wb
-	  && (regno == cfun->machine->frame.wb_pop_candidate1
-	      || regno == cfun->machine->frame.wb_pop_candidate2))
+	  && (regno == frame.wb_pop_candidate1
+	      || regno == frame.wb_pop_candidate2))
 	continue;
 
       machine_mode mode = aarch64_reg_save_mode (regno);
       reg = gen_rtx_REG (mode, regno);
-      offset = start_offset + cfun->machine->frame.reg_offset[regno];
+      offset = start_offset + frame.reg_offset[regno];
       rtx base_rtx = stack_pointer_rtx;
       if (mode == VNx2DImode && BYTES_BIG_ENDIAN)
 	aarch64_adjust_sve_callee_save_base (mode, base_rtx, anchor_reg,
@@ -9259,8 +9260,7 @@ aarch64_restore_callee_saves (poly_int64 start_offset, unsigned start,
 	  && (regno2 = aarch64_next_callee_save (regno + 1, limit)) <= limit
 	  && !cfun->machine->reg_is_wrapped_separately[regno2]
 	  && known_eq (GET_MODE_SIZE (mode),
-		       cfun->machine->frame.reg_offset[regno2]
-		       - cfun->machine->frame.reg_offset[regno]))
+		       frame.reg_offset[regno2] - frame.reg_offset[regno]))
 	{
 	  rtx reg2 = gen_rtx_REG (mode, regno2);
 	  rtx mem2;
@@ -9365,6 +9365,7 @@ offset_12bit_unsigned_scaled_p (machine_mode mode, poly_int64 offset)
 static sbitmap
 aarch64_get_separate_components (void)
 {
+  aarch64_frame &frame = cfun->machine->frame;
   sbitmap components = sbitmap_alloc (LAST_SAVED_REGNUM + 1);
   bitmap_clear (components);
 
@@ -9381,18 +9382,18 @@ aarch64_get_separate_components (void)
 	if (mode == VNx2DImode && BYTES_BIG_ENDIAN)
 	  continue;
 
-	poly_int64 offset = cfun->machine->frame.reg_offset[regno];
+	poly_int64 offset = frame.reg_offset[regno];
 
 	/* If the register is saved in the first SVE save slot, we use
 	   it as a stack probe for -fstack-clash-protection.  */
 	if (flag_stack_clash_protection
-	    && maybe_ne (cfun->machine->frame.below_hard_fp_saved_regs_size, 0)
+	    && maybe_ne (frame.below_hard_fp_saved_regs_size, 0)
 	    && known_eq (offset, 0))
 	  continue;
 
 	/* Get the offset relative to the register we'll use.  */
 	if (frame_pointer_needed)
-	  offset -= cfun->machine->frame.below_hard_fp_saved_regs_size;
+	  offset -= frame.below_hard_fp_saved_regs_size;
 	else
 	  offset += crtl->outgoing_args_size;
 
@@ -9411,11 +9412,11 @@ aarch64_get_separate_components (void)
   /* If the spare predicate register used by big-endian SVE code
      is call-preserved, it must be saved in the main prologue
      before any saves that use it.  */
-  if (cfun->machine->frame.spare_pred_reg != INVALID_REGNUM)
-    bitmap_clear_bit (components, cfun->machine->frame.spare_pred_reg);
+  if (frame.spare_pred_reg != INVALID_REGNUM)
+    bitmap_clear_bit (components, frame.spare_pred_reg);
 
-  unsigned reg1 = cfun->machine->frame.wb_push_candidate1;
-  unsigned reg2 = cfun->machine->frame.wb_push_candidate2;
+  unsigned reg1 = frame.wb_push_candidate1;
+  unsigned reg2 = frame.wb_push_candidate2;
   /* If registers have been chosen to be stored/restored with
      writeback don't interfere with them to avoid having to output explicit
      stack adjustment instructions.  */
@@ -9524,6 +9525,7 @@ aarch64_get_next_set_bit (sbitmap bmp, unsigned int start)
 static void
 aarch64_process_components (sbitmap components, bool prologue_p)
 {
+  aarch64_frame &frame = cfun->machine->frame;
   rtx ptr_reg = gen_rtx_REG (Pmode, frame_pointer_needed
 			     ? HARD_FRAME_POINTER_REGNUM
 			     : STACK_POINTER_REGNUM);
@@ -9538,9 +9540,9 @@ aarch64_process_components (sbitmap components, bool prologue_p)
       machine_mode mode = aarch64_reg_save_mode (regno);
       
       rtx reg = gen_rtx_REG (mode, regno);
-      poly_int64 offset = cfun->machine->frame.reg_offset[regno];
+      poly_int64 offset = frame.reg_offset[regno];
       if (frame_pointer_needed)
-	offset -= cfun->machine->frame.below_hard_fp_saved_regs_size;
+	offset -= frame.below_hard_fp_saved_regs_size;
       else
 	offset += crtl->outgoing_args_size;
 
@@ -9565,14 +9567,14 @@ aarch64_process_components (sbitmap components, bool prologue_p)
 	  break;
 	}
 
-      poly_int64 offset2 = cfun->machine->frame.reg_offset[regno2];
+      poly_int64 offset2 = frame.reg_offset[regno2];
       /* The next register is not of the same class or its offset is not
 	 mergeable with the current one into a pair.  */
       if (aarch64_sve_mode_p (mode)
 	  || !satisfies_constraint_Ump (mem)
 	  || GP_REGNUM_P (regno) != GP_REGNUM_P (regno2)
 	  || (crtl->abi->id () == ARM_PCS_SIMD && FP_REGNUM_P (regno))
-	  || maybe_ne ((offset2 - cfun->machine->frame.reg_offset[regno]),
+	  || maybe_ne ((offset2 - frame.reg_offset[regno]),
 		       GET_MODE_SIZE (mode)))
 	{
 	  insn = emit_insn (set);
@@ -9594,7 +9596,7 @@ aarch64_process_components (sbitmap components, bool prologue_p)
       /* REGNO2 can be saved/restored in a pair with REGNO.  */
       rtx reg2 = gen_rtx_REG (mode, regno2);
       if (frame_pointer_needed)
-	offset2 -= cfun->machine->frame.below_hard_fp_saved_regs_size;
+	offset2 -= frame.below_hard_fp_saved_regs_size;
       else
 	offset2 += crtl->outgoing_args_size;
       rtx addr2 = plus_constant (Pmode, ptr_reg, offset2);
@@ -9699,6 +9701,7 @@ aarch64_allocate_and_probe_stack_space (rtx temp1, rtx temp2,
 					bool frame_related_p,
 					bool final_adjustment_p)
 {
+  aarch64_frame &frame = cfun->machine->frame;
   HOST_WIDE_INT guard_size
     = 1 << param_stack_clash_protection_guard_size;
   HOST_WIDE_INT guard_used_by_caller = STACK_CLASH_CALLER_GUARD;
@@ -9719,25 +9722,25 @@ aarch64_allocate_and_probe_stack_space (rtx temp1, rtx temp2,
        register as a probe.  We can't assume that LR was saved at position 0
        though, so treat any space below it as unprobed.  */
   if (final_adjustment_p
-      && known_eq (cfun->machine->frame.below_hard_fp_saved_regs_size, 0))
+      && known_eq (frame.below_hard_fp_saved_regs_size, 0))
     {
-      poly_int64 lr_offset = cfun->machine->frame.reg_offset[LR_REGNUM];
+      poly_int64 lr_offset = frame.reg_offset[LR_REGNUM];
       if (known_ge (lr_offset, 0))
 	min_probe_threshold -= lr_offset.to_constant ();
       else
 	gcc_assert (!flag_stack_clash_protection || known_eq (poly_size, 0));
     }
 
-  poly_int64 frame_size = cfun->machine->frame.frame_size;
+  poly_int64 frame_size = frame.frame_size;
 
   /* We should always have a positive probe threshold.  */
   gcc_assert (min_probe_threshold > 0);
 
   if (flag_stack_clash_protection && !final_adjustment_p)
     {
-      poly_int64 initial_adjust = cfun->machine->frame.initial_adjust;
-      poly_int64 sve_callee_adjust = cfun->machine->frame.sve_callee_adjust;
-      poly_int64 final_adjust = cfun->machine->frame.final_adjust;
+      poly_int64 initial_adjust = frame.initial_adjust;
+      poly_int64 sve_callee_adjust = frame.sve_callee_adjust;
+      poly_int64 final_adjust = frame.final_adjust;
 
       if (known_eq (frame_size, 0))
 	{
@@ -10026,17 +10029,18 @@ aarch64_epilogue_uses (int regno)
 void
 aarch64_expand_prologue (void)
 {
-  poly_int64 frame_size = cfun->machine->frame.frame_size;
-  poly_int64 initial_adjust = cfun->machine->frame.initial_adjust;
-  HOST_WIDE_INT callee_adjust = cfun->machine->frame.callee_adjust;
-  poly_int64 final_adjust = cfun->machine->frame.final_adjust;
-  poly_int64 callee_offset = cfun->machine->frame.callee_offset;
-  poly_int64 sve_callee_adjust = cfun->machine->frame.sve_callee_adjust;
+  aarch64_frame &frame = cfun->machine->frame;
+  poly_int64 frame_size = frame.frame_size;
+  poly_int64 initial_adjust = frame.initial_adjust;
+  HOST_WIDE_INT callee_adjust = frame.callee_adjust;
+  poly_int64 final_adjust = frame.final_adjust;
+  poly_int64 callee_offset = frame.callee_offset;
+  poly_int64 sve_callee_adjust = frame.sve_callee_adjust;
   poly_int64 below_hard_fp_saved_regs_size
-    = cfun->machine->frame.below_hard_fp_saved_regs_size;
-  unsigned reg1 = cfun->machine->frame.wb_push_candidate1;
-  unsigned reg2 = cfun->machine->frame.wb_push_candidate2;
-  bool emit_frame_chain = cfun->machine->frame.emit_frame_chain;
+    = frame.below_hard_fp_saved_regs_size;
+  unsigned reg1 = frame.wb_push_candidate1;
+  unsigned reg2 = frame.wb_push_candidate2;
+  bool emit_frame_chain = frame.emit_frame_chain;
   rtx_insn *insn;
 
   if (flag_stack_clash_protection && known_eq (callee_adjust, 0))
@@ -10067,7 +10071,7 @@ aarch64_expand_prologue (void)
     }
 
   /* Push return address to shadow call stack.  */
-  if (cfun->machine->frame.is_scs_enabled)
+  if (frame.is_scs_enabled)
     emit_insn (gen_scs_push ());
 
   if (flag_stack_usage_info)
@@ -10106,7 +10110,7 @@ aarch64_expand_prologue (void)
 
   /* The offset of the frame chain record (if any) from the current SP.  */
   poly_int64 chain_offset = (initial_adjust + callee_adjust
-			     - cfun->machine->frame.hard_fp_offset);
+			     - frame.hard_fp_offset);
   gcc_assert (known_ge (chain_offset, 0));
 
   /* The offset of the bottom of the save area from the current SP.  */
@@ -10209,16 +10213,17 @@ aarch64_use_return_insn_p (void)
 void
 aarch64_expand_epilogue (bool for_sibcall)
 {
-  poly_int64 initial_adjust = cfun->machine->frame.initial_adjust;
-  HOST_WIDE_INT callee_adjust = cfun->machine->frame.callee_adjust;
-  poly_int64 final_adjust = cfun->machine->frame.final_adjust;
-  poly_int64 callee_offset = cfun->machine->frame.callee_offset;
-  poly_int64 sve_callee_adjust = cfun->machine->frame.sve_callee_adjust;
+  aarch64_frame &frame = cfun->machine->frame;
+  poly_int64 initial_adjust = frame.initial_adjust;
+  HOST_WIDE_INT callee_adjust = frame.callee_adjust;
+  poly_int64 final_adjust = frame.final_adjust;
+  poly_int64 callee_offset = frame.callee_offset;
+  poly_int64 sve_callee_adjust = frame.sve_callee_adjust;
   poly_int64 below_hard_fp_saved_regs_size
-    = cfun->machine->frame.below_hard_fp_saved_regs_size;
-  unsigned reg1 = cfun->machine->frame.wb_pop_candidate1;
-  unsigned reg2 = cfun->machine->frame.wb_pop_candidate2;
-  unsigned int last_gpr = (cfun->machine->frame.is_scs_enabled
+    = frame.below_hard_fp_saved_regs_size;
+  unsigned reg1 = frame.wb_pop_candidate1;
+  unsigned reg2 = frame.wb_pop_candidate2;
+  unsigned int last_gpr = (frame.is_scs_enabled
 			   ? R29_REGNUM : R30_REGNUM);
   rtx cfi_ops = NULL;
   rtx_insn *insn;
@@ -10252,7 +10257,7 @@ aarch64_expand_epilogue (bool for_sibcall)
   /* We need to add memory barrier to prevent read from deallocated stack.  */
   bool need_barrier_p
     = maybe_ne (get_frame_size ()
-		+ cfun->machine->frame.saved_varargs_size, 0);
+		+ frame.saved_varargs_size, 0);
 
   /* Emit a barrier to prevent loads from a deallocated stack.  */
   if (maybe_gt (final_adjust, crtl->outgoing_args_size)
@@ -10333,7 +10338,7 @@ aarch64_expand_epilogue (bool for_sibcall)
     }
 
   /* Pop return address from shadow call stack.  */
-  if (cfun->machine->frame.is_scs_enabled)
+  if (frame.is_scs_enabled)
     {
       machine_mode mode = aarch64_reg_save_mode (R30_REGNUM);
       rtx reg = gen_rtx_REG (mode, R30_REGNUM);
@@ -12840,24 +12845,24 @@ aarch64_can_eliminate (const int from ATTRIBUTE_UNUSED, const int to)
 poly_int64
 aarch64_initial_elimination_offset (unsigned from, unsigned to)
 {
+  aarch64_frame &frame = cfun->machine->frame;
+
   if (to == HARD_FRAME_POINTER_REGNUM)
     {
       if (from == ARG_POINTER_REGNUM)
-	return cfun->machine->frame.hard_fp_offset;
+	return frame.hard_fp_offset;
 
       if (from == FRAME_POINTER_REGNUM)
-	return cfun->machine->frame.hard_fp_offset
-	       - cfun->machine->frame.locals_offset;
+	return frame.hard_fp_offset - frame.locals_offset;
     }
 
   if (to == STACK_POINTER_REGNUM)
     {
       if (from == FRAME_POINTER_REGNUM)
-	  return cfun->machine->frame.frame_size
-		 - cfun->machine->frame.locals_offset;
+	return frame.frame_size - frame.locals_offset;
     }
 
-  return cfun->machine->frame.frame_size;
+  return frame.frame_size;
 }
 
 
-- 
2.25.1

[PATCH 02/19] aarch64: Avoid a use of callee_offset

[Richard Sandiford]

When we emit the frame chain, i.e. when we reach Here in this statement
of aarch64_expand_prologue:

  if (emit_frame_chain)
    {
      // Here
      ...
    }

the stack is in one of two states:

- We've allocated up to the frame chain, but no more.

- We've allocated the whole frame, and the frame chain is within easy
  reach of the new SP.

The offset of the frame chain from the current SP is available
in aarch64_frame as callee_offset.  It is also available as the
chain_offset local variable, where the latter is calculated from other
data.  (However, chain_offset is not always equal to callee_offset when
!emit_frame_chain, so chain_offset isn't redundant.)

In c600df9a4060da3c6121ff4d0b93f179eafd69d1 I switched to using
chain_offset for the initialisation of the hard frame pointer:

       aarch64_add_offset (Pmode, hard_frame_pointer_rtx,
-                         stack_pointer_rtx, callee_offset,
+                         stack_pointer_rtx, chain_offset,
                          tmp1_rtx, tmp0_rtx, frame_pointer_needed);

But the later REG_CFA_ADJUST_CFA handling still used callee_offset.

I think the difference is harmless, but it's more logical for the
CFA note to be in sync, and it's more convenient for later patches
if it uses chain_offset.

gcc/
	* config/aarch64/aarch64.cc (aarch64_expand_prologue): Use
	chain_offset rather than callee_offset.
---
 gcc/config/aarch64/aarch64.cc | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index b91f77d7b1f..9fb94623693 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -10034,7 +10034,6 @@ aarch64_expand_prologue (void)
   poly_int64 initial_adjust = frame.initial_adjust;
   HOST_WIDE_INT callee_adjust = frame.callee_adjust;
   poly_int64 final_adjust = frame.final_adjust;
-  poly_int64 callee_offset = frame.callee_offset;
   poly_int64 sve_callee_adjust = frame.sve_callee_adjust;
   poly_int64 below_hard_fp_saved_regs_size
     = frame.below_hard_fp_saved_regs_size;
@@ -10147,8 +10146,7 @@ aarch64_expand_prologue (void)
 	     implicit.  */
 	  if (!find_reg_note (insn, REG_CFA_ADJUST_CFA, NULL_RTX))
 	    {
-	      rtx src = plus_constant (Pmode, stack_pointer_rtx,
-				       callee_offset);
+	      rtx src = plus_constant (Pmode, stack_pointer_rtx, chain_offset);
 	      add_reg_note (insn, REG_CFA_ADJUST_CFA,
 			    gen_rtx_SET (hard_frame_pointer_rtx, src));
 	    }
-- 
2.25.1

[PATCH 03/19] aarch64: Explicitly handle frames with no saved registers

[Richard Sandiford]

If a frame has no saved registers, it can be allocated in one go.
There is no need to treat the areas below and above the saved
registers as separate.

And if we allocate the frame in one go, it should be allocated
as the initial_adjust rather than the final_adjust.  This allows the
frame size to grow to guard_size - guard_used_by_caller before a stack
probe is needed.  (A frame with no register saves is necessarily a
leaf frame.)

This is a no-op as thing stand, since a leaf function will have
no outgoing arguments, and so all the frame will be above where
the saved registers normally go.

gcc/
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Explicitly
	allocate the frame in one go if there are no saved registers.
---
 gcc/config/aarch64/aarch64.cc | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 9fb94623693..34d0ccc9a67 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8678,9 +8678,11 @@ aarch64_layout_frame (void)
 
   HOST_WIDE_INT const_size, const_outgoing_args_size, const_fp_offset;
   HOST_WIDE_INT const_saved_regs_size;
-  if (frame.frame_size.is_constant (&const_size)
-      && const_size < max_push_offset
-      && known_eq (frame.hard_fp_offset, const_size))
+  if (known_eq (frame.saved_regs_size, 0))
+    frame.initial_adjust = frame.frame_size;
+  else if (frame.frame_size.is_constant (&const_size)
+	   && const_size < max_push_offset
+	   && known_eq (frame.hard_fp_offset, const_size))
     {
       /* Simple, small frame with no outgoing arguments:
 
-- 
2.25.1

[PATCH 04/19] aarch64: Add bytes_below_saved_regs to frame info

[Richard Sandiford]

The frame layout code currently hard-codes the assumption that
the number of bytes below the saved registers is equal to the
size of the outgoing arguments.  This patch abstracts that
value into a new field of aarch64_frame.

gcc/
	* config/aarch64/aarch64.h (aarch64_frame::bytes_below_saved_regs): New
	field.
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Initialize it,
	and use it instead of crtl->outgoing_args_size.
	(aarch64_get_separate_components): Use bytes_below_saved_regs instead
	of outgoing_args_size.
	(aarch64_process_components): Likewise.
---
 gcc/config/aarch64/aarch64.cc | 71 ++++++++++++++++++-----------------
 gcc/config/aarch64/aarch64.h  |  5 +++
 2 files changed, 41 insertions(+), 35 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 34d0ccc9a67..49c2fbedd14 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8517,6 +8517,8 @@ aarch64_layout_frame (void)
   gcc_assert (crtl->is_leaf
 	      || maybe_ne (frame.reg_offset[R30_REGNUM], SLOT_NOT_REQUIRED));
 
+  frame.bytes_below_saved_regs = crtl->outgoing_args_size;
+
   /* Now assign stack slots for the registers.  Start with the predicate
      registers, since predicate LDR and STR have a relatively small
      offset range.  These saves happen below the hard frame pointer.  */
@@ -8621,18 +8623,18 @@ aarch64_layout_frame (void)
 
   poly_int64 varargs_and_saved_regs_size = offset + frame.saved_varargs_size;
 
-  poly_int64 above_outgoing_args
+  poly_int64 saved_regs_and_above
     = aligned_upper_bound (varargs_and_saved_regs_size
 			   + get_frame_size (),
 			   STACK_BOUNDARY / BITS_PER_UNIT);
 
   frame.hard_fp_offset
-    = above_outgoing_args - frame.below_hard_fp_saved_regs_size;
+    = saved_regs_and_above - frame.below_hard_fp_saved_regs_size;
 
   /* Both these values are already aligned.  */
-  gcc_assert (multiple_p (crtl->outgoing_args_size,
+  gcc_assert (multiple_p (frame.bytes_below_saved_regs,
 			  STACK_BOUNDARY / BITS_PER_UNIT));
-  frame.frame_size = above_outgoing_args + crtl->outgoing_args_size;
+  frame.frame_size = saved_regs_and_above + frame.bytes_below_saved_regs;
 
   frame.locals_offset = frame.saved_varargs_size;
 
@@ -8676,7 +8678,7 @@ aarch64_layout_frame (void)
   else if (frame.wb_pop_candidate1 != INVALID_REGNUM)
     max_push_offset = 256;
 
-  HOST_WIDE_INT const_size, const_outgoing_args_size, const_fp_offset;
+  HOST_WIDE_INT const_size, const_below_saved_regs, const_fp_offset;
   HOST_WIDE_INT const_saved_regs_size;
   if (known_eq (frame.saved_regs_size, 0))
     frame.initial_adjust = frame.frame_size;
@@ -8684,31 +8686,31 @@ aarch64_layout_frame (void)
 	   && const_size < max_push_offset
 	   && known_eq (frame.hard_fp_offset, const_size))
     {
-      /* Simple, small frame with no outgoing arguments:
+      /* Simple, small frame with no data below the saved registers.
 
 	 stp reg1, reg2, [sp, -frame_size]!
 	 stp reg3, reg4, [sp, 16]  */
       frame.callee_adjust = const_size;
     }
-  else if (crtl->outgoing_args_size.is_constant (&const_outgoing_args_size)
+  else if (frame.bytes_below_saved_regs.is_constant (&const_below_saved_regs)
 	   && frame.saved_regs_size.is_constant (&const_saved_regs_size)
-	   && const_outgoing_args_size + const_saved_regs_size < 512
-	   /* We could handle this case even with outgoing args, provided
-	      that the number of args left us with valid offsets for all
-	      predicate and vector save slots.  It's such a rare case that
-	      it hardly seems worth the effort though.  */
-	   && (!saves_below_hard_fp_p || const_outgoing_args_size == 0)
+	   && const_below_saved_regs + const_saved_regs_size < 512
+	   /* We could handle this case even with data below the saved
+	      registers, provided that that data left us with valid offsets
+	      for all predicate and vector save slots.  It's such a rare
+	      case that it hardly seems worth the effort though.  */
+	   && (!saves_below_hard_fp_p || const_below_saved_regs == 0)
 	   && !(cfun->calls_alloca
 		&& frame.hard_fp_offset.is_constant (&const_fp_offset)
 		&& const_fp_offset < max_push_offset))
     {
-      /* Frame with small outgoing arguments:
+      /* Frame with small area below the saved registers:
 
 	 sub sp, sp, frame_size
-	 stp reg1, reg2, [sp, outgoing_args_size]
-	 stp reg3, reg4, [sp, outgoing_args_size + 16]  */
+	 stp reg1, reg2, [sp, bytes_below_saved_regs]
+	 stp reg3, reg4, [sp, bytes_below_saved_regs + 16]  */
       frame.initial_adjust = frame.frame_size;
-      frame.callee_offset = const_outgoing_args_size;
+      frame.callee_offset = const_below_saved_regs;
     }
   else if (saves_below_hard_fp_p
 	   && known_eq (frame.saved_regs_size,
@@ -8718,30 +8720,29 @@ aarch64_layout_frame (void)
 
 	 sub sp, sp, hard_fp_offset + below_hard_fp_saved_regs_size
 	 save SVE registers relative to SP
-	 sub sp, sp, outgoing_args_size  */
+	 sub sp, sp, bytes_below_saved_regs  */
       frame.initial_adjust = (frame.hard_fp_offset
 			      + frame.below_hard_fp_saved_regs_size);
-      frame.final_adjust = crtl->outgoing_args_size;
+      frame.final_adjust = frame.bytes_below_saved_regs;
     }
   else if (frame.hard_fp_offset.is_constant (&const_fp_offset)
 	   && const_fp_offset < max_push_offset)
     {
-      /* Frame with large outgoing arguments or SVE saves, but with
-	 a small local area:
+      /* Frame with large area below the saved registers, or with SVE saves,
+	 but with a small area above:
 
 	 stp reg1, reg2, [sp, -hard_fp_offset]!
 	 stp reg3, reg4, [sp, 16]
 	 [sub sp, sp, below_hard_fp_saved_regs_size]
 	 [save SVE registers relative to SP]
-	 sub sp, sp, outgoing_args_size  */
+	 sub sp, sp, bytes_below_saved_regs  */
       frame.callee_adjust = const_fp_offset;
       frame.sve_callee_adjust = frame.below_hard_fp_saved_regs_size;
-      frame.final_adjust = crtl->outgoing_args_size;
+      frame.final_adjust = frame.bytes_below_saved_regs;
     }
   else
     {
-      /* Frame with large local area and outgoing arguments or SVE saves,
-	 using frame pointer:
+      /* General case:
 
 	 sub sp, sp, hard_fp_offset
 	 stp x29, x30, [sp, 0]
@@ -8749,10 +8750,10 @@ aarch64_layout_frame (void)
 	 stp reg3, reg4, [sp, 16]
 	 [sub sp, sp, below_hard_fp_saved_regs_size]
 	 [save SVE registers relative to SP]
-	 sub sp, sp, outgoing_args_size  */
+	 sub sp, sp, bytes_below_saved_regs  */
       frame.initial_adjust = frame.hard_fp_offset;
       frame.sve_callee_adjust = frame.below_hard_fp_saved_regs_size;
-      frame.final_adjust = crtl->outgoing_args_size;
+      frame.final_adjust = frame.bytes_below_saved_regs;
     }
 
   /* Make sure the individual adjustments add up to the full frame size.  */
@@ -9397,7 +9398,7 @@ aarch64_get_separate_components (void)
 	if (frame_pointer_needed)
 	  offset -= frame.below_hard_fp_saved_regs_size;
 	else
-	  offset += crtl->outgoing_args_size;
+	  offset += frame.bytes_below_saved_regs;
 
 	/* Check that we can access the stack slot of the register with one
 	   direct load with no adjustments needed.  */
@@ -9546,7 +9547,7 @@ aarch64_process_components (sbitmap components, bool prologue_p)
       if (frame_pointer_needed)
 	offset -= frame.below_hard_fp_saved_regs_size;
       else
-	offset += crtl->outgoing_args_size;
+	offset += frame.bytes_below_saved_regs;
 
       rtx addr = plus_constant (Pmode, ptr_reg, offset);
       rtx mem = gen_frame_mem (mode, addr);
@@ -9600,7 +9601,7 @@ aarch64_process_components (sbitmap components, bool prologue_p)
       if (frame_pointer_needed)
 	offset2 -= frame.below_hard_fp_saved_regs_size;
       else
-	offset2 += crtl->outgoing_args_size;
+	offset2 += frame.bytes_below_saved_regs;
       rtx addr2 = plus_constant (Pmode, ptr_reg, offset2);
       rtx mem2 = gen_frame_mem (mode, addr2);
       rtx set2 = prologue_p ? gen_rtx_SET (mem2, reg2)
@@ -9684,10 +9685,10 @@ aarch64_emit_stack_tie (rtx reg)
    registers.  If POLY_SIZE is not large enough to require a probe this function
    will only adjust the stack.  When allocating the stack space
    FRAME_RELATED_P is then used to indicate if the allocation is frame related.
-   FINAL_ADJUSTMENT_P indicates whether we are allocating the outgoing
-   arguments.  If we are then we ensure that any allocation larger than the ABI
-   defined buffer needs a probe so that the invariant of having a 1KB buffer is
-   maintained.
+   FINAL_ADJUSTMENT_P indicates whether we are allocating the area below
+   the saved registers.  If we are then we ensure that any allocation
+   larger than the ABI defined buffer needs a probe so that the
+   invariant of having a 1KB buffer is maintained.
 
    We emit barriers after each stack adjustment to prevent optimizations from
    breaking the invariant that we never drop the stack more than a page.  This
@@ -9896,7 +9897,7 @@ aarch64_allocate_and_probe_stack_space (rtx temp1, rtx temp2,
   /* Handle any residuals.  Residuals of at least MIN_PROBE_THRESHOLD have to
      be probed.  This maintains the requirement that each page is probed at
      least once.  For initial probing we probe only if the allocation is
-     more than GUARD_SIZE - buffer, and for the outgoing arguments we probe
+     more than GUARD_SIZE - buffer, and below the saved registers we probe
      if the amount is larger than buffer.  GUARD_SIZE - buffer + buffer ==
      GUARD_SIZE.  This works that for any allocation that is large enough to
      trigger a probe here, we'll have at least one, and if they're not large
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index c783cb96c48..83939991eb1 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -776,6 +776,11 @@ struct GTY (()) aarch64_frame
   /* The size of the callee-save registers with a slot in REG_OFFSET.  */
   poly_int64 saved_regs_size;
 
+  /* The number of bytes between the bottom of the static frame (the bottom
+     of the outgoing arguments) and the bottom of the register save area.
+     This value is always a multiple of STACK_BOUNDARY.  */
+  poly_int64 bytes_below_saved_regs;
+
   /* The size of the callee-save registers with a slot in REG_OFFSET that
      are saved below the hard frame pointer.  */
   poly_int64 below_hard_fp_saved_regs_size;
-- 
2.25.1

[PATCH 05/19] aarch64: Add bytes_below_hard_fp to frame info

[Richard Sandiford]

Following on from the previous bytes_below_saved_regs patch, this one
records the number of bytes that are below the hard frame pointer.
This eventually replaces below_hard_fp_saved_regs_size.

If a frame pointer is not needed, the epilogue adds final_adjust
to the stack pointer before restoring registers:

     aarch64_add_sp (tmp1_rtx, tmp0_rtx, final_adjust, true);

Therefore, if the epilogue needs to restore the stack pointer from
the hard frame pointer, the directly corresponding offset is:

     -bytes_below_hard_fp + final_adjust

i.e. go from the hard frame pointer to the bottom of the frame,
then add the same amount as if we were using the stack pointer
from the outset.

gcc/
	* config/aarch64/aarch64.h (aarch64_frame::bytes_below_hard_fp): New
	field.
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Initialize it.
	(aarch64_expand_epilogue): Use it instead of
	below_hard_fp_saved_regs_size.
---
 gcc/config/aarch64/aarch64.cc | 6 +++---
 gcc/config/aarch64/aarch64.h  | 5 +++++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 49c2fbedd14..58dd8946232 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8569,6 +8569,7 @@ aarch64_layout_frame (void)
      of the callee save area.  */
   bool saves_below_hard_fp_p = maybe_ne (offset, 0);
   frame.below_hard_fp_saved_regs_size = offset;
+  frame.bytes_below_hard_fp = offset + frame.bytes_below_saved_regs;
   if (frame.emit_frame_chain)
     {
       /* FP and LR are placed in the linkage record.  */
@@ -10220,8 +10221,7 @@ aarch64_expand_epilogue (bool for_sibcall)
   poly_int64 final_adjust = frame.final_adjust;
   poly_int64 callee_offset = frame.callee_offset;
   poly_int64 sve_callee_adjust = frame.sve_callee_adjust;
-  poly_int64 below_hard_fp_saved_regs_size
-    = frame.below_hard_fp_saved_regs_size;
+  poly_int64 bytes_below_hard_fp = frame.bytes_below_hard_fp;
   unsigned reg1 = frame.wb_pop_candidate1;
   unsigned reg2 = frame.wb_pop_candidate2;
   unsigned int last_gpr = (frame.is_scs_enabled
@@ -10279,7 +10279,7 @@ aarch64_expand_epilogue (bool for_sibcall)
        is restored on the instruction doing the writeback.  */
     aarch64_add_offset (Pmode, stack_pointer_rtx,
 			hard_frame_pointer_rtx,
-			-callee_offset - below_hard_fp_saved_regs_size,
+			-bytes_below_hard_fp + final_adjust,
 			tmp1_rtx, tmp0_rtx, callee_adjust == 0);
   else
      /* The case where we need to re-use the register here is very rare, so
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 83939991eb1..75fd3b59b0d 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -785,6 +785,11 @@ struct GTY (()) aarch64_frame
      are saved below the hard frame pointer.  */
   poly_int64 below_hard_fp_saved_regs_size;
 
+  /* The number of bytes between the bottom of the static frame (the bottom
+     of the outgoing arguments) and the hard frame pointer.  This value is
+     always a multiple of STACK_BOUNDARY.  */
+  poly_int64 bytes_below_hard_fp;
+
   /* Offset from the base of the frame (incomming SP) to the
      top of the locals area.  This value is always a multiple of
      STACK_BOUNDARY.  */
-- 
2.25.1

[PATCH 06/19] aarch64: Tweak aarch64_save/restore_callee_saves

[Richard Sandiford]

aarch64_save_callee_saves and aarch64_restore_callee_saves took
a parameter called start_offset that gives the offset of the
bottom of the saved register area from the current stack pointer.
However, it's more convenient for later patches if we use the
bottom of the entire frame as the reference point, rather than
the bottom of the saved registers.

Doing that removes the need for the callee_offset field.
Other than that, this is not a win on its own.  It only really
makes sense in combination with the follow-on patches.

gcc/
	* config/aarch64/aarch64.h (aarch64_frame::callee_offset): Delete.
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Remove
	callee_offset handling.
	(aarch64_save_callee_saves): Replace the start_offset parameter
	with a bytes_below_sp parameter.
	(aarch64_restore_callee_saves): Likewise.
	(aarch64_expand_prologue): Update accordingly.
	(aarch64_expand_epilogue): Likewise.
---
 gcc/config/aarch64/aarch64.cc | 56 +++++++++++++++++------------------
 gcc/config/aarch64/aarch64.h  |  4 ---
 2 files changed, 28 insertions(+), 32 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 58dd8946232..2c218c90906 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8643,7 +8643,6 @@ aarch64_layout_frame (void)
   frame.final_adjust = 0;
   frame.callee_adjust = 0;
   frame.sve_callee_adjust = 0;
-  frame.callee_offset = 0;
 
   frame.wb_pop_candidate1 = frame.wb_push_candidate1;
   frame.wb_pop_candidate2 = frame.wb_push_candidate2;
@@ -8711,7 +8710,6 @@ aarch64_layout_frame (void)
 	 stp reg1, reg2, [sp, bytes_below_saved_regs]
 	 stp reg3, reg4, [sp, bytes_below_saved_regs + 16]  */
       frame.initial_adjust = frame.frame_size;
-      frame.callee_offset = const_below_saved_regs;
     }
   else if (saves_below_hard_fp_p
 	   && known_eq (frame.saved_regs_size,
@@ -9112,12 +9110,13 @@ aarch64_add_cfa_expression (rtx_insn *insn, rtx reg,
 }
 
 /* Emit code to save the callee-saved registers from register number START
-   to LIMIT to the stack at the location starting at offset START_OFFSET,
-   skipping any write-back candidates if SKIP_WB is true.  HARD_FP_VALID_P
-   is true if the hard frame pointer has been set up.  */
+   to LIMIT to the stack.  The stack pointer is currently BYTES_BELOW_SP
+   bytes above the bottom of the static frame.  Skip any write-back
+   candidates if SKIP_WB is true.  HARD_FP_VALID_P is true if the hard
+   frame pointer has been set up.  */
 
 static void
-aarch64_save_callee_saves (poly_int64 start_offset,
+aarch64_save_callee_saves (poly_int64 bytes_below_sp,
 			   unsigned start, unsigned limit, bool skip_wb,
 			   bool hard_fp_valid_p)
 {
@@ -9145,7 +9144,9 @@ aarch64_save_callee_saves (poly_int64 start_offset,
 
       machine_mode mode = aarch64_reg_save_mode (regno);
       reg = gen_rtx_REG (mode, regno);
-      offset = start_offset + frame.reg_offset[regno];
+      offset = (frame.reg_offset[regno]
+		+ frame.bytes_below_saved_regs
+		- bytes_below_sp);
       rtx base_rtx = stack_pointer_rtx;
       poly_int64 sp_offset = offset;
 
@@ -9156,9 +9157,7 @@ aarch64_save_callee_saves (poly_int64 start_offset,
       else if (GP_REGNUM_P (regno)
 	       && (!offset.is_constant (&const_offset) || const_offset >= 512))
 	{
-	  gcc_assert (known_eq (start_offset, 0));
-	  poly_int64 fp_offset
-	    = frame.below_hard_fp_saved_regs_size;
+	  poly_int64 fp_offset = frame.bytes_below_hard_fp - bytes_below_sp;
 	  if (hard_fp_valid_p)
 	    base_rtx = hard_frame_pointer_rtx;
 	  else
@@ -9222,12 +9221,13 @@ aarch64_save_callee_saves (poly_int64 start_offset,
 }
 
 /* Emit code to restore the callee registers from register number START
-   up to and including LIMIT.  Restore from the stack offset START_OFFSET,
-   skipping any write-back candidates if SKIP_WB is true.  Write the
-   appropriate REG_CFA_RESTORE notes into CFI_OPS.  */
+   up to and including LIMIT.  The stack pointer is currently BYTES_BELOW_SP
+   bytes above the bottom of the static frame.  Skip any write-back
+   candidates if SKIP_WB is true.  Write the appropriate REG_CFA_RESTORE
+   notes into CFI_OPS.  */
 
 static void
-aarch64_restore_callee_saves (poly_int64 start_offset, unsigned start,
+aarch64_restore_callee_saves (poly_int64 bytes_below_sp, unsigned start,
 			      unsigned limit, bool skip_wb, rtx *cfi_ops)
 {
   aarch64_frame &frame = cfun->machine->frame;
@@ -9253,7 +9253,9 @@ aarch64_restore_callee_saves (poly_int64 start_offset, unsigned start,
 
       machine_mode mode = aarch64_reg_save_mode (regno);
       reg = gen_rtx_REG (mode, regno);
-      offset = start_offset + frame.reg_offset[regno];
+      offset = (frame.reg_offset[regno]
+		+ frame.bytes_below_saved_regs
+		- bytes_below_sp);
       rtx base_rtx = stack_pointer_rtx;
       if (mode == VNx2DImode && BYTES_BIG_ENDIAN)
 	aarch64_adjust_sve_callee_save_base (mode, base_rtx, anchor_reg,
@@ -10039,8 +10041,6 @@ aarch64_expand_prologue (void)
   HOST_WIDE_INT callee_adjust = frame.callee_adjust;
   poly_int64 final_adjust = frame.final_adjust;
   poly_int64 sve_callee_adjust = frame.sve_callee_adjust;
-  poly_int64 below_hard_fp_saved_regs_size
-    = frame.below_hard_fp_saved_regs_size;
   unsigned reg1 = frame.wb_push_candidate1;
   unsigned reg2 = frame.wb_push_candidate2;
   bool emit_frame_chain = frame.emit_frame_chain;
@@ -10116,8 +10116,8 @@ aarch64_expand_prologue (void)
 			     - frame.hard_fp_offset);
   gcc_assert (known_ge (chain_offset, 0));
 
-  /* The offset of the bottom of the save area from the current SP.  */
-  poly_int64 saved_regs_offset = chain_offset - below_hard_fp_saved_regs_size;
+  /* The offset of the current SP from the bottom of the static frame.  */
+  poly_int64 bytes_below_sp = frame_size - initial_adjust - callee_adjust;
 
   if (emit_frame_chain)
     {
@@ -10125,7 +10125,7 @@ aarch64_expand_prologue (void)
 	{
 	  reg1 = R29_REGNUM;
 	  reg2 = R30_REGNUM;
-	  aarch64_save_callee_saves (saved_regs_offset, reg1, reg2,
+	  aarch64_save_callee_saves (bytes_below_sp, reg1, reg2,
 				     false, false);
 	}
       else
@@ -10165,7 +10165,7 @@ aarch64_expand_prologue (void)
       aarch64_emit_stack_tie (hard_frame_pointer_rtx);
     }
 
-  aarch64_save_callee_saves (saved_regs_offset, R0_REGNUM, R30_REGNUM,
+  aarch64_save_callee_saves (bytes_below_sp, R0_REGNUM, R30_REGNUM,
 			     callee_adjust != 0 || emit_frame_chain,
 			     emit_frame_chain);
   if (maybe_ne (sve_callee_adjust, 0))
@@ -10175,16 +10175,17 @@ aarch64_expand_prologue (void)
       aarch64_allocate_and_probe_stack_space (tmp1_rtx, tmp0_rtx,
 					      sve_callee_adjust,
 					      !frame_pointer_needed, false);
-      saved_regs_offset += sve_callee_adjust;
+      bytes_below_sp -= sve_callee_adjust;
     }
-  aarch64_save_callee_saves (saved_regs_offset, P0_REGNUM, P15_REGNUM,
+  aarch64_save_callee_saves (bytes_below_sp, P0_REGNUM, P15_REGNUM,
 			     false, emit_frame_chain);
-  aarch64_save_callee_saves (saved_regs_offset, V0_REGNUM, V31_REGNUM,
+  aarch64_save_callee_saves (bytes_below_sp, V0_REGNUM, V31_REGNUM,
 			     callee_adjust != 0 || emit_frame_chain,
 			     emit_frame_chain);
 
   /* We may need to probe the final adjustment if it is larger than the guard
      that is assumed by the called.  */
+  gcc_assert (known_eq (bytes_below_sp, final_adjust));
   aarch64_allocate_and_probe_stack_space (tmp1_rtx, tmp0_rtx, final_adjust,
 					  !frame_pointer_needed, true);
 }
@@ -10219,7 +10220,6 @@ aarch64_expand_epilogue (bool for_sibcall)
   poly_int64 initial_adjust = frame.initial_adjust;
   HOST_WIDE_INT callee_adjust = frame.callee_adjust;
   poly_int64 final_adjust = frame.final_adjust;
-  poly_int64 callee_offset = frame.callee_offset;
   poly_int64 sve_callee_adjust = frame.sve_callee_adjust;
   poly_int64 bytes_below_hard_fp = frame.bytes_below_hard_fp;
   unsigned reg1 = frame.wb_pop_candidate1;
@@ -10289,9 +10289,9 @@ aarch64_expand_epilogue (bool for_sibcall)
 
   /* Restore the vector registers before the predicate registers,
      so that we can use P4 as a temporary for big-endian SVE frames.  */
-  aarch64_restore_callee_saves (callee_offset, V0_REGNUM, V31_REGNUM,
+  aarch64_restore_callee_saves (final_adjust, V0_REGNUM, V31_REGNUM,
 				callee_adjust != 0, &cfi_ops);
-  aarch64_restore_callee_saves (callee_offset, P0_REGNUM, P15_REGNUM,
+  aarch64_restore_callee_saves (final_adjust, P0_REGNUM, P15_REGNUM,
 				false, &cfi_ops);
   if (maybe_ne (sve_callee_adjust, 0))
     aarch64_add_sp (NULL_RTX, NULL_RTX, sve_callee_adjust, true);
@@ -10299,7 +10299,7 @@ aarch64_expand_epilogue (bool for_sibcall)
   /* When shadow call stack is enabled, the scs_pop in the epilogue will
      restore x30, we don't need to restore x30 again in the traditional
      way.  */
-  aarch64_restore_callee_saves (callee_offset - sve_callee_adjust,
+  aarch64_restore_callee_saves (final_adjust + sve_callee_adjust,
 				R0_REGNUM, last_gpr,
 				callee_adjust != 0, &cfi_ops);
 
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 75fd3b59b0d..46dd981b85c 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -812,10 +812,6 @@ struct GTY (()) aarch64_frame
      It is zero when no push is used.  */
   HOST_WIDE_INT callee_adjust;
 
-  /* The offset from SP to the callee-save registers after initial_adjust.
-     It may be non-zero if no push is used (ie. callee_adjust == 0).  */
-  poly_int64 callee_offset;
-
   /* The size of the stack adjustment before saving or after restoring
      SVE registers.  */
   poly_int64 sve_callee_adjust;
-- 
2.25.1

[PATCH 07/19] aarch64: Only calculate chain_offset if there is a chain

[Richard Sandiford]

After previous patches, it is no longer necessary to calculate
a chain_offset in cases where there is no chain record.

gcc/
	* config/aarch64/aarch64.cc (aarch64_expand_prologue): Move the
	calculation of chain_offset into the emit_frame_chain block.
---
 gcc/config/aarch64/aarch64.cc | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 2c218c90906..25b5fb243a6 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -10111,16 +10111,16 @@ aarch64_expand_prologue (void)
   if (callee_adjust != 0)
     aarch64_push_regs (reg1, reg2, callee_adjust);
 
-  /* The offset of the frame chain record (if any) from the current SP.  */
-  poly_int64 chain_offset = (initial_adjust + callee_adjust
-			     - frame.hard_fp_offset);
-  gcc_assert (known_ge (chain_offset, 0));
-
   /* The offset of the current SP from the bottom of the static frame.  */
   poly_int64 bytes_below_sp = frame_size - initial_adjust - callee_adjust;
 
   if (emit_frame_chain)
     {
+      /* The offset of the frame chain record (if any) from the current SP.  */
+      poly_int64 chain_offset = (initial_adjust + callee_adjust
+				 - frame.hard_fp_offset);
+      gcc_assert (known_ge (chain_offset, 0));
+
       if (callee_adjust == 0)
 	{
 	  reg1 = R29_REGNUM;
-- 
2.25.1

[PATCH 08/19] aarch64: Rename locals_offset to bytes_above_locals

[Richard Sandiford]

locals_offset was described as:

  /* Offset from the base of the frame (incomming SP) to the
     top of the locals area.  This value is always a multiple of
     STACK_BOUNDARY.  */

This is implicitly an “upside down” view of the frame: the incoming
SP is at offset 0, and anything N bytes below the incoming SP is at
offset N (rather than -N).

However, reg_offset instead uses a “right way up” view; that is,
it views offsets in address terms.  Something above X is at a
positive offset from X and something below X is at a negative
offset from X.

Also, even on FRAME_GROWS_DOWNWARD targets like AArch64,
target-independent code views offsets in address terms too:
locals are allocated at negative offsets to virtual_stack_vars.

It seems confusing to have *_offset fields of the same structure
using different polarities like this.  This patch tries to avoid
that by renaming locals_offset to bytes_above_locals.

gcc/
	* config/aarch64/aarch64.h (aarch64_frame::locals_offset): Rename to...
	(aarch64_frame::bytes_above_locals): ...this.
	* config/aarch64/aarch64.cc (aarch64_layout_frame)
	(aarch64_initial_elimination_offset): Update accordingly.
---
 gcc/config/aarch64/aarch64.cc | 6 +++---
 gcc/config/aarch64/aarch64.h  | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 25b5fb243a6..bcd1dec6f51 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8637,7 +8637,7 @@ aarch64_layout_frame (void)
 			  STACK_BOUNDARY / BITS_PER_UNIT));
   frame.frame_size = saved_regs_and_above + frame.bytes_below_saved_regs;
 
-  frame.locals_offset = frame.saved_varargs_size;
+  frame.bytes_above_locals = frame.saved_varargs_size;
 
   frame.initial_adjust = 0;
   frame.final_adjust = 0;
@@ -12854,13 +12854,13 @@ aarch64_initial_elimination_offset (unsigned from, unsigned to)
 	return frame.hard_fp_offset;
 
       if (from == FRAME_POINTER_REGNUM)
-	return frame.hard_fp_offset - frame.locals_offset;
+	return frame.hard_fp_offset - frame.bytes_above_locals;
     }
 
   if (to == STACK_POINTER_REGNUM)
     {
       if (from == FRAME_POINTER_REGNUM)
-	return frame.frame_size - frame.locals_offset;
+	return frame.frame_size - frame.bytes_above_locals;
     }
 
   return frame.frame_size;
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 46dd981b85c..3382f819e72 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -790,10 +790,10 @@ struct GTY (()) aarch64_frame
      always a multiple of STACK_BOUNDARY.  */
   poly_int64 bytes_below_hard_fp;
 
-  /* Offset from the base of the frame (incomming SP) to the
-     top of the locals area.  This value is always a multiple of
+  /* The number of bytes between the top of the locals area and the top
+     of the frame (the incomming SP).  This value is always a multiple of
      STACK_BOUNDARY.  */
-  poly_int64 locals_offset;
+  poly_int64 bytes_above_locals;
 
   /* Offset from the base of the frame (incomming SP) to the
      hard_frame_pointer.  This value is always a multiple of
-- 
2.25.1

[PATCH 09/19] aarch64: Rename hard_fp_offset to bytes_above_hard_fp

[Richard Sandiford]

Similarly to the previous locals_offset patch, hard_fp_offset
was described as:

  /* Offset from the base of the frame (incomming SP) to the
     hard_frame_pointer.  This value is always a multiple of
     STACK_BOUNDARY.  */
  poly_int64 hard_fp_offset;

which again took an “upside-down” view: higher offsets meant lower
addresses.  This patch renames the field to bytes_above_hard_fp instead.

gcc/
	* config/aarch64/aarch64.h (aarch64_frame::hard_fp_offset): Rename
	to...
	(aarch64_frame::bytes_above_hard_fp): ...this.
	* config/aarch64/aarch64.cc (aarch64_layout_frame)
	(aarch64_expand_prologue): Update accordingly.
	(aarch64_initial_elimination_offset): Likewise.
---
 gcc/config/aarch64/aarch64.cc | 26 +++++++++++++-------------
 gcc/config/aarch64/aarch64.h  |  6 +++---
 2 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index bcd1dec6f51..7d642d06871 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8629,7 +8629,7 @@ aarch64_layout_frame (void)
 			   + get_frame_size (),
 			   STACK_BOUNDARY / BITS_PER_UNIT);
 
-  frame.hard_fp_offset
+  frame.bytes_above_hard_fp
     = saved_regs_and_above - frame.below_hard_fp_saved_regs_size;
 
   /* Both these values are already aligned.  */
@@ -8678,13 +8678,13 @@ aarch64_layout_frame (void)
   else if (frame.wb_pop_candidate1 != INVALID_REGNUM)
     max_push_offset = 256;
 
-  HOST_WIDE_INT const_size, const_below_saved_regs, const_fp_offset;
+  HOST_WIDE_INT const_size, const_below_saved_regs, const_above_fp;
   HOST_WIDE_INT const_saved_regs_size;
   if (known_eq (frame.saved_regs_size, 0))
     frame.initial_adjust = frame.frame_size;
   else if (frame.frame_size.is_constant (&const_size)
 	   && const_size < max_push_offset
-	   && known_eq (frame.hard_fp_offset, const_size))
+	   && known_eq (frame.bytes_above_hard_fp, const_size))
     {
       /* Simple, small frame with no data below the saved registers.
 
@@ -8701,8 +8701,8 @@ aarch64_layout_frame (void)
 	      case that it hardly seems worth the effort though.  */
 	   && (!saves_below_hard_fp_p || const_below_saved_regs == 0)
 	   && !(cfun->calls_alloca
-		&& frame.hard_fp_offset.is_constant (&const_fp_offset)
-		&& const_fp_offset < max_push_offset))
+		&& frame.bytes_above_hard_fp.is_constant (&const_above_fp)
+		&& const_above_fp < max_push_offset))
     {
       /* Frame with small area below the saved registers:
 
@@ -8720,12 +8720,12 @@ aarch64_layout_frame (void)
 	 sub sp, sp, hard_fp_offset + below_hard_fp_saved_regs_size
 	 save SVE registers relative to SP
 	 sub sp, sp, bytes_below_saved_regs  */
-      frame.initial_adjust = (frame.hard_fp_offset
+      frame.initial_adjust = (frame.bytes_above_hard_fp
 			      + frame.below_hard_fp_saved_regs_size);
       frame.final_adjust = frame.bytes_below_saved_regs;
     }
-  else if (frame.hard_fp_offset.is_constant (&const_fp_offset)
-	   && const_fp_offset < max_push_offset)
+  else if (frame.bytes_above_hard_fp.is_constant (&const_above_fp)
+	   && const_above_fp < max_push_offset)
     {
       /* Frame with large area below the saved registers, or with SVE saves,
 	 but with a small area above:
@@ -8735,7 +8735,7 @@ aarch64_layout_frame (void)
 	 [sub sp, sp, below_hard_fp_saved_regs_size]
 	 [save SVE registers relative to SP]
 	 sub sp, sp, bytes_below_saved_regs  */
-      frame.callee_adjust = const_fp_offset;
+      frame.callee_adjust = const_above_fp;
       frame.sve_callee_adjust = frame.below_hard_fp_saved_regs_size;
       frame.final_adjust = frame.bytes_below_saved_regs;
     }
@@ -8750,7 +8750,7 @@ aarch64_layout_frame (void)
 	 [sub sp, sp, below_hard_fp_saved_regs_size]
 	 [save SVE registers relative to SP]
 	 sub sp, sp, bytes_below_saved_regs  */
-      frame.initial_adjust = frame.hard_fp_offset;
+      frame.initial_adjust = frame.bytes_above_hard_fp;
       frame.sve_callee_adjust = frame.below_hard_fp_saved_regs_size;
       frame.final_adjust = frame.bytes_below_saved_regs;
     }
@@ -10118,7 +10118,7 @@ aarch64_expand_prologue (void)
     {
       /* The offset of the frame chain record (if any) from the current SP.  */
       poly_int64 chain_offset = (initial_adjust + callee_adjust
-				 - frame.hard_fp_offset);
+				 - frame.bytes_above_hard_fp);
       gcc_assert (known_ge (chain_offset, 0));
 
       if (callee_adjust == 0)
@@ -12851,10 +12851,10 @@ aarch64_initial_elimination_offset (unsigned from, unsigned to)
   if (to == HARD_FRAME_POINTER_REGNUM)
     {
       if (from == ARG_POINTER_REGNUM)
-	return frame.hard_fp_offset;
+	return frame.bytes_above_hard_fp;
 
       if (from == FRAME_POINTER_REGNUM)
-	return frame.hard_fp_offset - frame.bytes_above_locals;
+	return frame.bytes_above_hard_fp - frame.bytes_above_locals;
     }
 
   if (to == STACK_POINTER_REGNUM)
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 3382f819e72..4a4de9c044e 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -795,10 +795,10 @@ struct GTY (()) aarch64_frame
      STACK_BOUNDARY.  */
   poly_int64 bytes_above_locals;
 
-  /* Offset from the base of the frame (incomming SP) to the
-     hard_frame_pointer.  This value is always a multiple of
+  /* The number of bytes between the hard_frame_pointer and the top of
+     the frame (the incomming SP).  This value is always a multiple of
      STACK_BOUNDARY.  */
-  poly_int64 hard_fp_offset;
+  poly_int64 bytes_above_hard_fp;
 
   /* The size of the frame.  This value is the offset from base of the
      frame (incomming SP) to the stack_pointer.  This value is always
-- 
2.25.1

[PATCH 10/19] aarch64: Tweak frame_size comment

[Richard Sandiford]

This patch fixes another case in which a value was described with
an “upside-down” view.

gcc/
	* config/aarch64/aarch64.h (aarch64_frame::frame_size): Tweak comment.
---
 gcc/config/aarch64/aarch64.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 4a4de9c044e..92965eced0a 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -800,8 +800,8 @@ struct GTY (()) aarch64_frame
      STACK_BOUNDARY.  */
   poly_int64 bytes_above_hard_fp;
 
-  /* The size of the frame.  This value is the offset from base of the
-     frame (incomming SP) to the stack_pointer.  This value is always
+  /* The size of the frame, i.e. the number of bytes between the bottom
+     of the outgoing arguments and the incoming SP.  This value is always
      a multiple of STACK_BOUNDARY.  */
   poly_int64 frame_size;
 
-- 
2.25.1

[PATCH 11/19] aarch64: Measure reg_offset from the bottom of the frame

[Richard Sandiford]

reg_offset was measured from the bottom of the saved register area.
This made perfect sense with the original layout, since the bottom
of the saved register area was also the hard frame pointer address.
It became slightly less obvious with SVE, since we save SVE
registers below the hard frame pointer, but it still made sense.

However, if we want to allow different frame layouts, it's more
convenient and obvious to measure reg_offset from the bottom of
the frame.  After previous patches, it's also a slight simplification
in its own right.

gcc/
	* config/aarch64/aarch64.h (aarch64_frame): Add comment above
	reg_offset.
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Walk offsets
	from the bottom of the frame, rather than the bottom of the saved
	register area.  Measure reg_offset from the bottom of the frame
	rather than the bottom of the saved register area.
	(aarch64_save_callee_saves): Update accordingly.
	(aarch64_restore_callee_saves): Likewise.
	(aarch64_get_separate_components): Likewise.
	(aarch64_process_components): Likewise.
---
 gcc/config/aarch64/aarch64.cc | 53 ++++++++++++++++-------------------
 gcc/config/aarch64/aarch64.h  |  3 ++
 2 files changed, 27 insertions(+), 29 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 7d642d06871..ca2e6af5d12 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8439,7 +8439,6 @@ aarch64_needs_frame_chain (void)
 static void
 aarch64_layout_frame (void)
 {
-  poly_int64 offset = 0;
   int regno, last_fp_reg = INVALID_REGNUM;
   machine_mode vector_save_mode = aarch64_reg_save_mode (V8_REGNUM);
   poly_int64 vector_save_size = GET_MODE_SIZE (vector_save_mode);
@@ -8517,7 +8516,9 @@ aarch64_layout_frame (void)
   gcc_assert (crtl->is_leaf
 	      || maybe_ne (frame.reg_offset[R30_REGNUM], SLOT_NOT_REQUIRED));
 
-  frame.bytes_below_saved_regs = crtl->outgoing_args_size;
+  poly_int64 offset = crtl->outgoing_args_size;
+  gcc_assert (multiple_p (offset, STACK_BOUNDARY / BITS_PER_UNIT));
+  frame.bytes_below_saved_regs = offset;
 
   /* Now assign stack slots for the registers.  Start with the predicate
      registers, since predicate LDR and STR have a relatively small
@@ -8529,7 +8530,8 @@ aarch64_layout_frame (void)
 	offset += BYTES_PER_SVE_PRED;
       }
 
-  if (maybe_ne (offset, 0))
+  poly_int64 saved_prs_size = offset - frame.bytes_below_saved_regs;
+  if (maybe_ne (saved_prs_size, 0))
     {
       /* If we have any vector registers to save above the predicate registers,
 	 the offset of the vector register save slots need to be a multiple
@@ -8547,10 +8549,10 @@ aarch64_layout_frame (void)
 	offset = aligned_upper_bound (offset, STACK_BOUNDARY / BITS_PER_UNIT);
       else
 	{
-	  if (known_le (offset, vector_save_size))
-	    offset = vector_save_size;
-	  else if (known_le (offset, vector_save_size * 2))
-	    offset = vector_save_size * 2;
+	  if (known_le (saved_prs_size, vector_save_size))
+	    offset = frame.bytes_below_saved_regs + vector_save_size;
+	  else if (known_le (saved_prs_size, vector_save_size * 2))
+	    offset = frame.bytes_below_saved_regs + vector_save_size * 2;
 	  else
 	    gcc_unreachable ();
 	}
@@ -8567,9 +8569,10 @@ aarch64_layout_frame (void)
 
   /* OFFSET is now the offset of the hard frame pointer from the bottom
      of the callee save area.  */
-  bool saves_below_hard_fp_p = maybe_ne (offset, 0);
-  frame.below_hard_fp_saved_regs_size = offset;
-  frame.bytes_below_hard_fp = offset + frame.bytes_below_saved_regs;
+  frame.below_hard_fp_saved_regs_size = offset - frame.bytes_below_saved_regs;
+  bool saves_below_hard_fp_p
+    = maybe_ne (frame.below_hard_fp_saved_regs_size, 0);
+  frame.bytes_below_hard_fp = offset;
   if (frame.emit_frame_chain)
     {
       /* FP and LR are placed in the linkage record.  */
@@ -8620,9 +8623,10 @@ aarch64_layout_frame (void)
 
   offset = aligned_upper_bound (offset, STACK_BOUNDARY / BITS_PER_UNIT);
 
-  frame.saved_regs_size = offset;
+  frame.saved_regs_size = offset - frame.bytes_below_saved_regs;
 
-  poly_int64 varargs_and_saved_regs_size = offset + frame.saved_varargs_size;
+  poly_int64 varargs_and_saved_regs_size
+    = frame.saved_regs_size + frame.saved_varargs_size;
 
   poly_int64 saved_regs_and_above
     = aligned_upper_bound (varargs_and_saved_regs_size
@@ -9144,9 +9148,7 @@ aarch64_save_callee_saves (poly_int64 bytes_below_sp,
 
       machine_mode mode = aarch64_reg_save_mode (regno);
       reg = gen_rtx_REG (mode, regno);
-      offset = (frame.reg_offset[regno]
-		+ frame.bytes_below_saved_regs
-		- bytes_below_sp);
+      offset = frame.reg_offset[regno] - bytes_below_sp;
       rtx base_rtx = stack_pointer_rtx;
       poly_int64 sp_offset = offset;
 
@@ -9253,9 +9255,7 @@ aarch64_restore_callee_saves (poly_int64 bytes_below_sp, unsigned start,
 
       machine_mode mode = aarch64_reg_save_mode (regno);
       reg = gen_rtx_REG (mode, regno);
-      offset = (frame.reg_offset[regno]
-		+ frame.bytes_below_saved_regs
-		- bytes_below_sp);
+      offset = frame.reg_offset[regno] - bytes_below_sp;
       rtx base_rtx = stack_pointer_rtx;
       if (mode == VNx2DImode && BYTES_BIG_ENDIAN)
 	aarch64_adjust_sve_callee_save_base (mode, base_rtx, anchor_reg,
@@ -9394,14 +9394,12 @@ aarch64_get_separate_components (void)
 	   it as a stack probe for -fstack-clash-protection.  */
 	if (flag_stack_clash_protection
 	    && maybe_ne (frame.below_hard_fp_saved_regs_size, 0)
-	    && known_eq (offset, 0))
+	    && known_eq (offset, frame.bytes_below_saved_regs))
 	  continue;
 
 	/* Get the offset relative to the register we'll use.  */
 	if (frame_pointer_needed)
-	  offset -= frame.below_hard_fp_saved_regs_size;
-	else
-	  offset += frame.bytes_below_saved_regs;
+	  offset -= frame.bytes_below_hard_fp;
 
 	/* Check that we can access the stack slot of the register with one
 	   direct load with no adjustments needed.  */
@@ -9548,9 +9546,7 @@ aarch64_process_components (sbitmap components, bool prologue_p)
       rtx reg = gen_rtx_REG (mode, regno);
       poly_int64 offset = frame.reg_offset[regno];
       if (frame_pointer_needed)
-	offset -= frame.below_hard_fp_saved_regs_size;
-      else
-	offset += frame.bytes_below_saved_regs;
+	offset -= frame.bytes_below_hard_fp;
 
       rtx addr = plus_constant (Pmode, ptr_reg, offset);
       rtx mem = gen_frame_mem (mode, addr);
@@ -9602,9 +9598,7 @@ aarch64_process_components (sbitmap components, bool prologue_p)
       /* REGNO2 can be saved/restored in a pair with REGNO.  */
       rtx reg2 = gen_rtx_REG (mode, regno2);
       if (frame_pointer_needed)
-	offset2 -= frame.below_hard_fp_saved_regs_size;
-      else
-	offset2 += frame.bytes_below_saved_regs;
+	offset2 -= frame.bytes_below_hard_fp;
       rtx addr2 = plus_constant (Pmode, ptr_reg, offset2);
       rtx mem2 = gen_frame_mem (mode, addr2);
       rtx set2 = prologue_p ? gen_rtx_SET (mem2, reg2)
@@ -9730,7 +9724,8 @@ aarch64_allocate_and_probe_stack_space (rtx temp1, rtx temp2,
   if (final_adjustment_p
       && known_eq (frame.below_hard_fp_saved_regs_size, 0))
     {
-      poly_int64 lr_offset = frame.reg_offset[LR_REGNUM];
+      poly_int64 lr_offset = (frame.reg_offset[LR_REGNUM]
+			      - frame.bytes_below_saved_regs);
       if (known_ge (lr_offset, 0))
 	min_probe_threshold -= lr_offset.to_constant ();
       else
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 92965eced0a..3e891107e5d 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -765,6 +765,9 @@ extern enum aarch64_processor aarch64_tune;
 #ifdef HAVE_POLY_INT_H
 struct GTY (()) aarch64_frame
 {
+  /* The offset from the bottom of the static frame (the bottom of the
+     outgoing arguments) of each register save slot, or -2 if no save is
+     needed.  */
   poly_int64 reg_offset[LAST_SAVED_REGNUM + 1];
 
   /* The number of extra stack bytes taken up by register varargs.
-- 
2.25.1

[PATCH 12/19] aarch64: Simplify top of frame allocation

[Richard Sandiford]

After previous patches, it no longer really makes sense to allocate
the top of the frame in terms of varargs_and_saved_regs_size and
saved_regs_and_above.

gcc/
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Simplify
	the allocation of the top of the frame.
---
 gcc/config/aarch64/aarch64.cc | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index ca2e6af5d12..9578592d256 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8625,23 +8625,16 @@ aarch64_layout_frame (void)
 
   frame.saved_regs_size = offset - frame.bytes_below_saved_regs;
 
-  poly_int64 varargs_and_saved_regs_size
-    = frame.saved_regs_size + frame.saved_varargs_size;
-
-  poly_int64 saved_regs_and_above
-    = aligned_upper_bound (varargs_and_saved_regs_size
-			   + get_frame_size (),
-			   STACK_BOUNDARY / BITS_PER_UNIT);
-
-  frame.bytes_above_hard_fp
-    = saved_regs_and_above - frame.below_hard_fp_saved_regs_size;
+  offset += get_frame_size ();
+  offset = aligned_upper_bound (offset, STACK_BOUNDARY / BITS_PER_UNIT);
+  auto top_of_locals = offset;
 
-  /* Both these values are already aligned.  */
-  gcc_assert (multiple_p (frame.bytes_below_saved_regs,
-			  STACK_BOUNDARY / BITS_PER_UNIT));
-  frame.frame_size = saved_regs_and_above + frame.bytes_below_saved_regs;
+  offset += frame.saved_varargs_size;
+  gcc_assert (multiple_p (offset, STACK_BOUNDARY / BITS_PER_UNIT));
+  frame.frame_size = offset;
 
-  frame.bytes_above_locals = frame.saved_varargs_size;
+  frame.bytes_above_hard_fp = frame.frame_size - frame.bytes_below_hard_fp;
+  frame.bytes_above_locals = frame.frame_size - top_of_locals;
 
   frame.initial_adjust = 0;
   frame.final_adjust = 0;
-- 
2.25.1

[PATCH 13/19] aarch64: Minor initial adjustment tweak

[Richard Sandiford]

This patch just changes a calculation of initial_adjust
to one that makes it slightly more obvious that the total
adjustment is frame.frame_size.

gcc/
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Tweak
	calculation of initial_adjust for frames in which all saves
	are SVE saves.
---
 gcc/config/aarch64/aarch64.cc | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 9578592d256..e40ccc7d1cf 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8714,11 +8714,10 @@ aarch64_layout_frame (void)
     {
       /* Frame in which all saves are SVE saves:
 
-	 sub sp, sp, hard_fp_offset + below_hard_fp_saved_regs_size
+	 sub sp, sp, frame_size - bytes_below_saved_regs
 	 save SVE registers relative to SP
 	 sub sp, sp, bytes_below_saved_regs  */
-      frame.initial_adjust = (frame.bytes_above_hard_fp
-			      + frame.below_hard_fp_saved_regs_size);
+      frame.initial_adjust = frame.frame_size - frame.bytes_below_saved_regs;
       frame.final_adjust = frame.bytes_below_saved_regs;
     }
   else if (frame.bytes_above_hard_fp.is_constant (&const_above_fp)
-- 
2.25.1

[PATCH 14/19] aarch64: Tweak stack clash boundary condition

[Richard Sandiford]

The AArch64 ABI says that, when stack clash protection is used,
there can be a maximum of 1KiB of unprobed space at sp on entry
to a function.  Therefore, we need to probe when allocating
>= guard_size - 1KiB of data (>= rather than >).  This is what
GCC does.

If an allocation is exactly guard_size bytes, it is enough to allocate
those bytes and probe once at offset 1024.  It isn't possible to use a
single probe at any other offset: higher would conmplicate later code,
by leaving more unprobed space than usual, while lower would risk
leaving an entire page unprobed.  For simplicity, the code probes all
allocations at offset 1024.

Some register saves also act as probes.  If we need to allocate
more space below the last such register save probe, we need to
probe the allocation if it is > 1KiB.  Again, this allocation is
then sometimes (but not always) probed at offset 1024.  This sort of
allocation is currently only used for outgoing arguments, which are
rarely this big.

However, the code also probed if this final outgoing-arguments
allocation was == 1KiB, rather than just > 1KiB.  This isn't
necessary, since the register save then probes at offset 1024
as required.  Continuing to probe allocations of exactly 1KiB
would complicate later patches.

gcc/
	* config/aarch64/aarch64.cc (aarch64_allocate_and_probe_stack_space):
	Don't probe final allocations that are exactly 1KiB in size (after
	unprobed space above the final allocation has been deducted).

gcc/testsuite/
	* gcc.target/aarch64/stack-check-prologue-17.c: New test.
---
 gcc/config/aarch64/aarch64.cc                 |  4 +-
 .../aarch64/stack-check-prologue-17.c         | 55 +++++++++++++++++++
 2 files changed, 58 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-17.c

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index e40ccc7d1cf..b942bf3de4a 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -9697,9 +9697,11 @@ aarch64_allocate_and_probe_stack_space (rtx temp1, rtx temp2,
   HOST_WIDE_INT guard_size
     = 1 << param_stack_clash_protection_guard_size;
   HOST_WIDE_INT guard_used_by_caller = STACK_CLASH_CALLER_GUARD;
+  HOST_WIDE_INT byte_sp_alignment = STACK_BOUNDARY / BITS_PER_UNIT;
+  gcc_assert (multiple_p (poly_size, byte_sp_alignment));
   HOST_WIDE_INT min_probe_threshold
     = (final_adjustment_p
-       ? guard_used_by_caller
+       ? guard_used_by_caller + byte_sp_alignment
        : guard_size - guard_used_by_caller);
   /* When doing the final adjustment for the outgoing arguments, take into
      account any unprobed space there is above the current SP.  There are
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-17.c b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-17.c
new file mode 100644
index 00000000000..0d8a25d73a2
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-17.c
@@ -0,0 +1,55 @@
+/* { dg-options "-O2 -fstack-clash-protection -fomit-frame-pointer --param stack-clash-protection-guard-size=12" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+void f(int, ...);
+void g();
+
+/*
+** test1:
+**	...
+**	str	x30, \[sp\]
+**	sub	sp, sp, #1024
+**	cbnz	w0, .*
+**	bl	g
+**	...
+*/
+int test1(int z) {
+  __uint128_t x = 0;
+  int y[0x400];
+  if (z)
+    {
+      f(0, 0, 0, 0, 0, 0, 0, &y,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x);
+    }
+  g();
+  return 1;
+}
+
+/*
+** test2:
+**	...
+**	str	x30, \[sp\]
+**	sub	sp, sp, #1040
+**	str	xzr, \[sp\]
+**	cbnz	w0, .*
+**	bl	g
+**	...
+*/
+int test2(int z) {
+  __uint128_t x = 0;
+  int y[0x400];
+  if (z)
+    {
+      f(0, 0, 0, 0, 0, 0, 0, &y,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x);
+    }
+  g();
+  return 1;
+}
-- 
2.25.1

[PATCH 15/19] aarch64: Put LR save probe in first 16 bytes

[Richard Sandiford]

-fstack-clash-protection uses the save of LR as a probe for the next
allocation.  The next allocation could be:

* another part of the static frame, e.g. when allocating SVE save slots
  or outgoing arguments

* an alloca in the same function

* an allocation made by a callee function

However, when -fomit-frame-pointer is used, the LR save slot is placed
above the other GPR save slots.  It could therefore be up to 80 bytes
above the base of the GPR save area (which is also the hard fp address).

aarch64_allocate_and_probe_stack_space took this into account when
deciding how much subsequent space could be allocated without needing
a probe.  However, it interacted badly with:

      /* If doing a small final adjustment, we always probe at offset 0.
	 This is done to avoid issues when LR is not at position 0 or when
	 the final adjustment is smaller than the probing offset.  */
      else if (final_adjustment_p && rounded_size == 0)
	residual_probe_offset = 0;

which forces any allocation that is smaller than the guard page size
to be probed at offset 0 rather than the usual offset 1024.  It was
therefore possible to construct cases in which we had:

* a probe using LR at SP + 80 bytes (or some other value >= 16)
* an allocation of the guard page size - 16 bytes
* a probe at SP + 0

which allocates guard page size + 64 consecutive unprobed bytes.

This patch requires the LR probe to be in the first 16 bytes of the
save area when stack clash protection is active.  Doing it
unconditionally would cause code-quality regressions.

Putting LR before other registers prevents push/pop allocation
when shadow call stacks are enabled, since LR is restored
separately from the other callee-saved registers.

The new comment doesn't say that the probe register is required
to be LR, since a later patch removes that restriction.

gcc/
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Ensure that
	the LR save slot is in the first 16 bytes of the register save area.
	Only form STP/LDP push/pop candidates if both registers are valid.
	(aarch64_allocate_and_probe_stack_space): Remove workaround for
	when LR was not in the first 16 bytes.

gcc/testsuite/
	* gcc.target/aarch64/stack-check-prologue-18.c: New test.
	* gcc.target/aarch64/stack-check-prologue-19.c: Likewise.
	* gcc.target/aarch64/stack-check-prologue-20.c: Likewise.
---
 gcc/config/aarch64/aarch64.cc                 |  72 ++++++-------
 .../aarch64/stack-check-prologue-18.c         | 100 ++++++++++++++++++
 .../aarch64/stack-check-prologue-19.c         | 100 ++++++++++++++++++
 .../aarch64/stack-check-prologue-20.c         |   3 +
 4 files changed, 233 insertions(+), 42 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-18.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-19.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-check-prologue-20.c

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index b942bf3de4a..383b32f2078 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8573,26 +8573,34 @@ aarch64_layout_frame (void)
   bool saves_below_hard_fp_p
     = maybe_ne (frame.below_hard_fp_saved_regs_size, 0);
   frame.bytes_below_hard_fp = offset;
+
+  auto allocate_gpr_slot = [&](unsigned int regno)
+    {
+      frame.reg_offset[regno] = offset;
+      if (frame.wb_push_candidate1 == INVALID_REGNUM)
+	frame.wb_push_candidate1 = regno;
+      else if (frame.wb_push_candidate2 == INVALID_REGNUM)
+	frame.wb_push_candidate2 = regno;
+      offset += UNITS_PER_WORD;
+    };
+
   if (frame.emit_frame_chain)
     {
       /* FP and LR are placed in the linkage record.  */
-      frame.reg_offset[R29_REGNUM] = offset;
-      frame.wb_push_candidate1 = R29_REGNUM;
-      frame.reg_offset[R30_REGNUM] = offset + UNITS_PER_WORD;
-      frame.wb_push_candidate2 = R30_REGNUM;
-      offset += 2 * UNITS_PER_WORD;
+      allocate_gpr_slot (R29_REGNUM);
+      allocate_gpr_slot (R30_REGNUM);
     }
+  else if (flag_stack_clash_protection
+	   && known_eq (frame.reg_offset[R30_REGNUM], SLOT_REQUIRED))
+    /* Put the LR save slot first, since it makes a good choice of probe
+       for stack clash purposes.  The idea is that the link register usually
+       has to be saved before a call anyway, and so we lose little by
+       stopping it from being individually shrink-wrapped.  */
+    allocate_gpr_slot (R30_REGNUM);
 
   for (regno = R0_REGNUM; regno <= R30_REGNUM; regno++)
     if (known_eq (frame.reg_offset[regno], SLOT_REQUIRED))
-      {
-	frame.reg_offset[regno] = offset;
-	if (frame.wb_push_candidate1 == INVALID_REGNUM)
-	  frame.wb_push_candidate1 = regno;
-	else if (frame.wb_push_candidate2 == INVALID_REGNUM)
-	  frame.wb_push_candidate2 = regno;
-	offset += UNITS_PER_WORD;
-      }
+      allocate_gpr_slot (regno);
 
   poly_int64 max_int_offset = offset;
   offset = aligned_upper_bound (offset, STACK_BOUNDARY / BITS_PER_UNIT);
@@ -8670,10 +8678,13 @@ aarch64_layout_frame (void)
      max_push_offset to 0, because no registers are popped at this time,
      so callee_adjust cannot be adjusted.  */
   HOST_WIDE_INT max_push_offset = 0;
-  if (frame.wb_pop_candidate2 != INVALID_REGNUM)
-    max_push_offset = 512;
-  else if (frame.wb_pop_candidate1 != INVALID_REGNUM)
-    max_push_offset = 256;
+  if (frame.wb_pop_candidate1 != INVALID_REGNUM)
+    {
+      if (frame.wb_pop_candidate2 != INVALID_REGNUM)
+	max_push_offset = 512;
+      else
+	max_push_offset = 256;
+    }
 
   HOST_WIDE_INT const_size, const_below_saved_regs, const_above_fp;
   HOST_WIDE_INT const_saved_regs_size;
@@ -9703,29 +9714,6 @@ aarch64_allocate_and_probe_stack_space (rtx temp1, rtx temp2,
     = (final_adjustment_p
        ? guard_used_by_caller + byte_sp_alignment
        : guard_size - guard_used_by_caller);
-  /* When doing the final adjustment for the outgoing arguments, take into
-     account any unprobed space there is above the current SP.  There are
-     two cases:
-
-     - When saving SVE registers below the hard frame pointer, we force
-       the lowest save to take place in the prologue before doing the final
-       adjustment (i.e. we don't allow the save to be shrink-wrapped).
-       This acts as a probe at SP, so there is no unprobed space.
-
-     - When there are no SVE register saves, we use the store of the link
-       register as a probe.  We can't assume that LR was saved at position 0
-       though, so treat any space below it as unprobed.  */
-  if (final_adjustment_p
-      && known_eq (frame.below_hard_fp_saved_regs_size, 0))
-    {
-      poly_int64 lr_offset = (frame.reg_offset[LR_REGNUM]
-			      - frame.bytes_below_saved_regs);
-      if (known_ge (lr_offset, 0))
-	min_probe_threshold -= lr_offset.to_constant ();
-      else
-	gcc_assert (!flag_stack_clash_protection || known_eq (poly_size, 0));
-    }
-
   poly_int64 frame_size = frame.frame_size;
 
   /* We should always have a positive probe threshold.  */
@@ -9905,8 +9893,8 @@ aarch64_allocate_and_probe_stack_space (rtx temp1, rtx temp2,
       if (final_adjustment_p && rounded_size != 0)
 	min_probe_threshold = 0;
       /* If doing a small final adjustment, we always probe at offset 0.
-	 This is done to avoid issues when LR is not at position 0 or when
-	 the final adjustment is smaller than the probing offset.  */
+	 This is done to avoid issues when the final adjustment is smaller
+	 than the probing offset.  */
       else if (final_adjustment_p && rounded_size == 0)
 	residual_probe_offset = 0;
 
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-18.c b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-18.c
new file mode 100644
index 00000000000..82447d20fff
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-18.c
@@ -0,0 +1,100 @@
+/* { dg-options "-O2 -fstack-clash-protection -fomit-frame-pointer --param stack-clash-protection-guard-size=12" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+void f(int, ...);
+void g();
+
+/*
+** test1:
+**	...
+**	str	x30, \[sp\]
+**	sub	sp, sp, #4064
+**	str	xzr, \[sp\]
+**	cbnz	w0, .*
+**	bl	g
+**	...
+**	str	x26, \[sp, #?4128\]
+**	...
+*/
+int test1(int z) {
+  __uint128_t x = 0;
+  int y[0x400];
+  if (z)
+    {
+      asm volatile ("" :::
+		    "x19", "x20", "x21", "x22", "x23", "x24", "x25", "x26");
+      f(0, 0, 0, 0, 0, 0, 0, &y,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x);
+    }
+  g();
+  return 1;
+}
+
+/*
+** test2:
+**	...
+**	str	x30, \[sp\]
+**	sub	sp, sp, #1040
+**	str	xzr, \[sp\]
+**	cbnz	w0, .*
+**	bl	g
+**	...
+*/
+int test2(int z) {
+  __uint128_t x = 0;
+  int y[0x400];
+  if (z)
+    {
+      asm volatile ("" :::
+		    "x19", "x20", "x21", "x22", "x23", "x24", "x25", "x26");
+      f(0, 0, 0, 0, 0, 0, 0, &y,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x);
+    }
+  g();
+  return 1;
+}
+
+/*
+** test3:
+**	...
+**	str	x30, \[sp\]
+**	sub	sp, sp, #1024
+**	cbnz	w0, .*
+**	bl	g
+**	...
+*/
+int test3(int z) {
+  __uint128_t x = 0;
+  int y[0x400];
+  if (z)
+    {
+      asm volatile ("" :::
+		    "x19", "x20", "x21", "x22", "x23", "x24", "x25", "x26");
+      f(0, 0, 0, 0, 0, 0, 0, &y,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x);
+    }
+  g();
+  return 1;
+}
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-19.c b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-19.c
new file mode 100644
index 00000000000..73ac3e4e4eb
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-19.c
@@ -0,0 +1,100 @@
+/* { dg-options "-O2 -fstack-clash-protection -fomit-frame-pointer --param stack-clash-protection-guard-size=12 -fsanitize=shadow-call-stack -ffixed-x18" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+void f(int, ...);
+void g();
+
+/*
+** test1:
+**	...
+**	str	x30, \[sp\]
+**	sub	sp, sp, #4064
+**	str	xzr, \[sp\]
+**	cbnz	w0, .*
+**	bl	g
+**	...
+**	str	x26, \[sp, #?4128\]
+**	...
+*/
+int test1(int z) {
+  __uint128_t x = 0;
+  int y[0x400];
+  if (z)
+    {
+      asm volatile ("" :::
+		    "x19", "x20", "x21", "x22", "x23", "x24", "x25", "x26");
+      f(0, 0, 0, 0, 0, 0, 0, &y,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x);
+    }
+  g();
+  return 1;
+}
+
+/*
+** test2:
+**	...
+**	str	x30, \[sp\]
+**	sub	sp, sp, #1040
+**	str	xzr, \[sp\]
+**	cbnz	w0, .*
+**	bl	g
+**	...
+*/
+int test2(int z) {
+  __uint128_t x = 0;
+  int y[0x400];
+  if (z)
+    {
+      asm volatile ("" :::
+		    "x19", "x20", "x21", "x22", "x23", "x24", "x25", "x26");
+      f(0, 0, 0, 0, 0, 0, 0, &y,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x);
+    }
+  g();
+  return 1;
+}
+
+/*
+** test3:
+**	...
+**	str	x30, \[sp\]
+**	sub	sp, sp, #1024
+**	cbnz	w0, .*
+**	bl	g
+**	...
+*/
+int test3(int z) {
+  __uint128_t x = 0;
+  int y[0x400];
+  if (z)
+    {
+      asm volatile ("" :::
+		    "x19", "x20", "x21", "x22", "x23", "x24", "x25", "x26");
+      f(0, 0, 0, 0, 0, 0, 0, &y,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x,
+	x, x, x, x, x, x, x, x, x, x, x, x, x, x, x, x);
+    }
+  g();
+  return 1;
+}
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-20.c b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-20.c
new file mode 100644
index 00000000000..690aae8dfd5
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-20.c
@@ -0,0 +1,3 @@
+/* { dg-options "-O2 -fstack-protector-all -fstack-clash-protection -fomit-frame-pointer --param stack-clash-protection-guard-size=12 -fsanitize=shadow-call-stack -ffixed-x18" } */
+
+#include "stack-check-prologue-19.c"
-- 
2.25.1

[PATCH 16/19] aarch64: Simplify probe of final frame allocation

[Richard Sandiford]

Previous patches ensured that the final frame allocation only needs
a probe when the size is strictly greater than 1KiB.  It's therefore
safe to use the normal 1024 probe offset in all cases.

The main motivation for doing this is to simplify the code and
remove the number of special cases.

gcc/
	* config/aarch64/aarch64.cc (aarch64_allocate_and_probe_stack_space):
	Always probe the residual allocation at offset 1024, asserting
	that that is in range.

gcc/testsuite/
	* gcc.target/aarch64/stack-check-prologue-17.c: Expect the probe
	to be at offset 1024 rather than offset 0.
	* gcc.target/aarch64/stack-check-prologue-18.c: Likewise.
	* gcc.target/aarch64/stack-check-prologue-19.c: Likewise.
---
 gcc/config/aarch64/aarch64.cc                        | 12 ++++--------
 .../gcc.target/aarch64/stack-check-prologue-17.c     |  2 +-
 .../gcc.target/aarch64/stack-check-prologue-18.c     |  4 ++--
 .../gcc.target/aarch64/stack-check-prologue-19.c     |  4 ++--
 4 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 383b32f2078..bcb879ba94b 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -9887,16 +9887,12 @@ aarch64_allocate_and_probe_stack_space (rtx temp1, rtx temp2,
      are still safe.  */
   if (residual)
     {
-      HOST_WIDE_INT residual_probe_offset = guard_used_by_caller;
+      gcc_assert (guard_used_by_caller + byte_sp_alignment <= size);
+
       /* If we're doing final adjustments, and we've done any full page
 	 allocations then any residual needs to be probed.  */
       if (final_adjustment_p && rounded_size != 0)
 	min_probe_threshold = 0;
-      /* If doing a small final adjustment, we always probe at offset 0.
-	 This is done to avoid issues when the final adjustment is smaller
-	 than the probing offset.  */
-      else if (final_adjustment_p && rounded_size == 0)
-	residual_probe_offset = 0;
 
       aarch64_sub_sp (temp1, temp2, residual, frame_related_p);
       if (residual >= min_probe_threshold)
@@ -9907,8 +9903,8 @@ aarch64_allocate_and_probe_stack_space (rtx temp1, rtx temp2,
 		     HOST_WIDE_INT_PRINT_DEC " bytes, probing will be required."
 		     "\n", residual);
 
-	    emit_stack_probe (plus_constant (Pmode, stack_pointer_rtx,
-					     residual_probe_offset));
+	  emit_stack_probe (plus_constant (Pmode, stack_pointer_rtx,
+					   guard_used_by_caller));
 	  emit_insn (gen_blockage ());
 	}
     }
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-17.c b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-17.c
index 0d8a25d73a2..f0ec1389771 100644
--- a/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-17.c
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-17.c
@@ -33,7 +33,7 @@ int test1(int z) {
 **	...
 **	str	x30, \[sp\]
 **	sub	sp, sp, #1040
-**	str	xzr, \[sp\]
+**	str	xzr, \[sp, #?1024\]
 **	cbnz	w0, .*
 **	bl	g
 **	...
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-18.c b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-18.c
index 82447d20fff..6383bec5ebc 100644
--- a/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-18.c
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-18.c
@@ -9,7 +9,7 @@ void g();
 **	...
 **	str	x30, \[sp\]
 **	sub	sp, sp, #4064
-**	str	xzr, \[sp\]
+**	str	xzr, \[sp, #?1024\]
 **	cbnz	w0, .*
 **	bl	g
 **	...
@@ -50,7 +50,7 @@ int test1(int z) {
 **	...
 **	str	x30, \[sp\]
 **	sub	sp, sp, #1040
-**	str	xzr, \[sp\]
+**	str	xzr, \[sp, #?1024\]
 **	cbnz	w0, .*
 **	bl	g
 **	...
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-19.c b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-19.c
index 73ac3e4e4eb..562039b5e9b 100644
--- a/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-19.c
+++ b/gcc/testsuite/gcc.target/aarch64/stack-check-prologue-19.c
@@ -9,7 +9,7 @@ void g();
 **	...
 **	str	x30, \[sp\]
 **	sub	sp, sp, #4064
-**	str	xzr, \[sp\]
+**	str	xzr, \[sp, #?1024\]
 **	cbnz	w0, .*
 **	bl	g
 **	...
@@ -50,7 +50,7 @@ int test1(int z) {
 **	...
 **	str	x30, \[sp\]
 **	sub	sp, sp, #1040
-**	str	xzr, \[sp\]
+**	str	xzr, \[sp, #?1024\]
 **	cbnz	w0, .*
 **	bl	g
 **	...
-- 
2.25.1

[PATCH 17/19] aarch64: Explicitly record probe registers in frame info

[Richard Sandiford]

The stack frame is currently divided into three areas:

A: the area above the hard frame pointer
B: the SVE saves below the hard frame pointer
C: the outgoing arguments

If the stack frame is allocated in one chunk, the allocation needs a
probe if the frame size is >= guard_size - 1KiB.  In addition, if the
function is not a leaf function, it must probe an address no more than
1KiB above the outgoing SP.  We ensured the second condition by

(1) using single-chunk allocations for non-leaf functions only if
    the link register save slot is within 512 bytes of the bottom
    of the frame; and

(2) using the link register save as a probe (meaning, for instance,
    that it can't be individually shrink wrapped)

If instead the stack is allocated in multiple chunks, then:

* an allocation involving only the outgoing arguments (C above) requires
  a probe if the allocation size is > 1KiB

* any other allocation requires a probe if the allocation size
  is >= guard_size - 1KiB

* second and subsequent allocations require the previous allocation
  to probe at the bottom of the allocated area, regardless of the size
  of that previous allocation

The final point means that, unlike for single allocations,
it can be necessary to have both a non-SVE register probe and
an SVE register probe.  For example:

* allocate A, probe using a non-SVE register save
* allocate B, probe using an SVE register save
* allocate C

The non-SVE register used in this case was again the link register.
It was previously used even if the link register save slot was some
bytes above the bottom of the non-SVE register saves, but an earlier
patch avoided that by putting the link register save slot first.

As a belt-and-braces fix, this patch explicitly records which
probe registers we're using and allows the non-SVE probe to be
whichever register comes first (as for SVE).

The patch also avoids unnecessary probes in sve/pcs/stack_clash_3.c.

gcc/
	* config/aarch64/aarch64.h (aarch64_frame::sve_save_and_probe)
	(aarch64_frame::hard_fp_save_and_probe): New fields.
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Initialize them.
	Rather than asserting that a leaf function saves LR, instead assert
	that a leaf function saves something.
	(aarch64_get_separate_components): Prevent the chosen probe
	registers from being individually shrink-wrapped.
	(aarch64_allocate_and_probe_stack_space): Remove workaround for
	probe registers that aren't at the bottom of the previous allocation.

gcc/testsuite/
	* gcc.target/aarch64/sve/pcs/stack_clash_3.c: Avoid redundant probes.
---
 gcc/config/aarch64/aarch64.cc                 | 68 +++++++++++++++----
 gcc/config/aarch64/aarch64.h                  |  8 +++
 .../aarch64/sve/pcs/stack_clash_3.c           |  6 +-
 3 files changed, 64 insertions(+), 18 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index bcb879ba94b..3c7c476c4c6 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8510,15 +8510,11 @@ aarch64_layout_frame (void)
 	&& !crtl->abi->clobbers_full_reg_p (regno))
       frame.reg_offset[regno] = SLOT_REQUIRED;
 
-  /* With stack-clash, LR must be saved in non-leaf functions.  The saving of
-     LR counts as an implicit probe which allows us to maintain the invariant
-     described in the comment at expand_prologue.  */
-  gcc_assert (crtl->is_leaf
-	      || maybe_ne (frame.reg_offset[R30_REGNUM], SLOT_NOT_REQUIRED));
 
   poly_int64 offset = crtl->outgoing_args_size;
   gcc_assert (multiple_p (offset, STACK_BOUNDARY / BITS_PER_UNIT));
   frame.bytes_below_saved_regs = offset;
+  frame.sve_save_and_probe = INVALID_REGNUM;
 
   /* Now assign stack slots for the registers.  Start with the predicate
      registers, since predicate LDR and STR have a relatively small
@@ -8526,6 +8522,8 @@ aarch64_layout_frame (void)
   for (regno = P0_REGNUM; regno <= P15_REGNUM; regno++)
     if (known_eq (frame.reg_offset[regno], SLOT_REQUIRED))
       {
+	if (frame.sve_save_and_probe == INVALID_REGNUM)
+	  frame.sve_save_and_probe = regno;
 	frame.reg_offset[regno] = offset;
 	offset += BYTES_PER_SVE_PRED;
       }
@@ -8563,6 +8561,8 @@ aarch64_layout_frame (void)
     for (regno = V0_REGNUM; regno <= V31_REGNUM; regno++)
       if (known_eq (frame.reg_offset[regno], SLOT_REQUIRED))
 	{
+	  if (frame.sve_save_and_probe == INVALID_REGNUM)
+	    frame.sve_save_and_probe = regno;
 	  frame.reg_offset[regno] = offset;
 	  offset += vector_save_size;
 	}
@@ -8572,10 +8572,18 @@ aarch64_layout_frame (void)
   frame.below_hard_fp_saved_regs_size = offset - frame.bytes_below_saved_regs;
   bool saves_below_hard_fp_p
     = maybe_ne (frame.below_hard_fp_saved_regs_size, 0);
+  gcc_assert (!saves_below_hard_fp_p
+	      || (frame.sve_save_and_probe != INVALID_REGNUM
+		  && known_eq (frame.reg_offset[frame.sve_save_and_probe],
+			       frame.bytes_below_saved_regs)));
+
   frame.bytes_below_hard_fp = offset;
+  frame.hard_fp_save_and_probe = INVALID_REGNUM;
 
   auto allocate_gpr_slot = [&](unsigned int regno)
     {
+      if (frame.hard_fp_save_and_probe == INVALID_REGNUM)
+	frame.hard_fp_save_and_probe = regno;
       frame.reg_offset[regno] = offset;
       if (frame.wb_push_candidate1 == INVALID_REGNUM)
 	frame.wb_push_candidate1 = regno;
@@ -8609,6 +8617,8 @@ aarch64_layout_frame (void)
   for (regno = V0_REGNUM; regno <= V31_REGNUM; regno++)
     if (known_eq (frame.reg_offset[regno], SLOT_REQUIRED))
       {
+	if (frame.hard_fp_save_and_probe == INVALID_REGNUM)
+	  frame.hard_fp_save_and_probe = regno;
 	/* If there is an alignment gap between integer and fp callee-saves,
 	   allocate the last fp register to it if possible.  */
 	if (regno == last_fp_reg
@@ -8632,6 +8642,17 @@ aarch64_layout_frame (void)
   offset = aligned_upper_bound (offset, STACK_BOUNDARY / BITS_PER_UNIT);
 
   frame.saved_regs_size = offset - frame.bytes_below_saved_regs;
+  gcc_assert (known_eq (frame.saved_regs_size,
+			frame.below_hard_fp_saved_regs_size)
+	      || (frame.hard_fp_save_and_probe != INVALID_REGNUM
+		  && known_eq (frame.reg_offset[frame.hard_fp_save_and_probe],
+			       frame.bytes_below_hard_fp)));
+
+  /* With stack-clash, a register must be saved in non-leaf functions.
+     The saving of the bottommost register counts as an implicit probe,
+     which allows us to maintain the invariant described in the comment
+     at expand_prologue.  */
+  gcc_assert (crtl->is_leaf || maybe_ne (frame.saved_regs_size, 0));
 
   offset += get_frame_size ();
   offset = aligned_upper_bound (offset, STACK_BOUNDARY / BITS_PER_UNIT);
@@ -8762,6 +8783,25 @@ aarch64_layout_frame (void)
       frame.final_adjust = frame.bytes_below_saved_regs;
     }
 
+  /* The frame is allocated in pieces, with each non-final piece
+     including a register save at offset 0 that acts as a probe for
+     the following piece.  In addition, the save of the bottommost register
+     acts as a probe for callees and allocas.  Roll back any probes that
+     aren't needed.
+
+     A probe isn't needed if it is associated with the final allocation
+     (including callees and allocas) that happens before the epilogue is
+     executed.  */
+  if (crtl->is_leaf
+      && !cfun->calls_alloca
+      && known_eq (frame.final_adjust, 0))
+    {
+      if (maybe_ne (frame.sve_callee_adjust, 0))
+	frame.sve_save_and_probe = INVALID_REGNUM;
+      else
+	frame.hard_fp_save_and_probe = INVALID_REGNUM;
+    }
+
   /* Make sure the individual adjustments add up to the full frame size.  */
   gcc_assert (known_eq (frame.initial_adjust
 			+ frame.callee_adjust
@@ -9393,13 +9433,6 @@ aarch64_get_separate_components (void)
 
 	poly_int64 offset = frame.reg_offset[regno];
 
-	/* If the register is saved in the first SVE save slot, we use
-	   it as a stack probe for -fstack-clash-protection.  */
-	if (flag_stack_clash_protection
-	    && maybe_ne (frame.below_hard_fp_saved_regs_size, 0)
-	    && known_eq (offset, frame.bytes_below_saved_regs))
-	  continue;
-
 	/* Get the offset relative to the register we'll use.  */
 	if (frame_pointer_needed)
 	  offset -= frame.bytes_below_hard_fp;
@@ -9434,6 +9467,13 @@ aarch64_get_separate_components (void)
 
   bitmap_clear_bit (components, LR_REGNUM);
   bitmap_clear_bit (components, SP_REGNUM);
+  if (flag_stack_clash_protection)
+    {
+      if (frame.sve_save_and_probe != INVALID_REGNUM)
+	bitmap_clear_bit (components, frame.sve_save_and_probe);
+      if (frame.hard_fp_save_and_probe != INVALID_REGNUM)
+	bitmap_clear_bit (components, frame.hard_fp_save_and_probe);
+    }
 
   return components;
 }
@@ -9980,8 +10020,8 @@ aarch64_epilogue_uses (int regno)
    When probing is needed, we emit a probe at the start of the prologue
    and every PARAM_STACK_CLASH_PROTECTION_GUARD_SIZE bytes thereafter.
 
-   We have to track how much space has been allocated and the only stores
-   to the stack we track as implicit probes are the FP/LR stores.
+   We can also use register saves as probes.  These are stored in
+   sve_save_and_probe and hard_fp_save_and_probe.
 
    For outgoing arguments we probe if the size is larger than 1KB, such that
    the ABI specified buffer is maintained for the next callee.
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 3e891107e5d..8fcebeb5206 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -862,6 +862,14 @@ struct GTY (()) aarch64_frame
      This is the register they should use.  */
   unsigned spare_pred_reg;
 
+  /* An SVE register that is saved below the hard frame pointer and that acts
+     as a probe for later allocations, or INVALID_REGNUM if none.  */
+  unsigned sve_save_and_probe;
+
+  /* A register that is saved at the hard frame pointer and that acts
+     as a probe for later allocations, or INVALID_REGNUM if none.  */
+  unsigned hard_fp_save_and_probe;
+
   bool laid_out;
 
   /* True if shadow call stack should be enabled for the current function.  */
diff --git a/gcc/testsuite/gcc.target/aarch64/sve/pcs/stack_clash_3.c b/gcc/testsuite/gcc.target/aarch64/sve/pcs/stack_clash_3.c
index 3e01ec36c3a..3530a0d504b 100644
--- a/gcc/testsuite/gcc.target/aarch64/sve/pcs/stack_clash_3.c
+++ b/gcc/testsuite/gcc.target/aarch64/sve/pcs/stack_clash_3.c
@@ -11,11 +11,10 @@
 **	mov	x11, sp
 **	...
 **	sub	sp, sp, x13
-**	str	p4, \[sp\]
 **	cbz	w0, [^\n]*
+**	str	p4, \[sp\]
 **	...
 **	ptrue	p0\.b, all
-**	ldr	p4, \[sp\]
 **	addvl	sp, sp, #1
 **	ldr	x24, \[sp\], 32
 **	ret
@@ -39,13 +38,12 @@ test_1 (int n)
 **	mov	x11, sp
 **	...
 **	sub	sp, sp, x13
-**	str	p4, \[sp\]
 **	cbz	w0, [^\n]*
+**	str	p4, \[sp\]
 **	str	p5, \[sp, #1, mul vl\]
 **	str	p6, \[sp, #2, mul vl\]
 **	...
 **	ptrue	p0\.b, all
-**	ldr	p4, \[sp\]
 **	addvl	sp, sp, #1
 **	ldr	x24, \[sp\], 32
 **	ret
-- 
2.25.1

[PATCH 18/19] aarch64: Remove below_hard_fp_saved_regs_size

[Richard Sandiford]

After previous patches, it's no longer necessary to store
saved_regs_size and below_hard_fp_saved_regs_size in the frame info.
All measurements instead use the top or bottom of the frame as
reference points.

gcc/
	* config/aarch64/aarch64.h (aarch64_frame::saved_regs_size)
	(aarch64_frame::below_hard_fp_saved_regs_size): Delete.
	* config/aarch64/aarch64.cc (aarch64_layout_frame): Update accordingly.
---
 gcc/config/aarch64/aarch64.cc | 45 ++++++++++++++++-------------------
 gcc/config/aarch64/aarch64.h  |  7 ------
 2 files changed, 21 insertions(+), 31 deletions(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 3c7c476c4c6..51e57370807 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8569,9 +8569,8 @@ aarch64_layout_frame (void)
 
   /* OFFSET is now the offset of the hard frame pointer from the bottom
      of the callee save area.  */
-  frame.below_hard_fp_saved_regs_size = offset - frame.bytes_below_saved_regs;
-  bool saves_below_hard_fp_p
-    = maybe_ne (frame.below_hard_fp_saved_regs_size, 0);
+  auto below_hard_fp_saved_regs_size = offset - frame.bytes_below_saved_regs;
+  bool saves_below_hard_fp_p = maybe_ne (below_hard_fp_saved_regs_size, 0);
   gcc_assert (!saves_below_hard_fp_p
 	      || (frame.sve_save_and_probe != INVALID_REGNUM
 		  && known_eq (frame.reg_offset[frame.sve_save_and_probe],
@@ -8641,9 +8640,8 @@ aarch64_layout_frame (void)
 
   offset = aligned_upper_bound (offset, STACK_BOUNDARY / BITS_PER_UNIT);
 
-  frame.saved_regs_size = offset - frame.bytes_below_saved_regs;
-  gcc_assert (known_eq (frame.saved_regs_size,
-			frame.below_hard_fp_saved_regs_size)
+  auto saved_regs_size = offset - frame.bytes_below_saved_regs;
+  gcc_assert (known_eq (saved_regs_size, below_hard_fp_saved_regs_size)
 	      || (frame.hard_fp_save_and_probe != INVALID_REGNUM
 		  && known_eq (frame.reg_offset[frame.hard_fp_save_and_probe],
 			       frame.bytes_below_hard_fp)));
@@ -8652,7 +8650,7 @@ aarch64_layout_frame (void)
      The saving of the bottommost register counts as an implicit probe,
      which allows us to maintain the invariant described in the comment
      at expand_prologue.  */
-  gcc_assert (crtl->is_leaf || maybe_ne (frame.saved_regs_size, 0));
+  gcc_assert (crtl->is_leaf || maybe_ne (saved_regs_size, 0));
 
   offset += get_frame_size ();
   offset = aligned_upper_bound (offset, STACK_BOUNDARY / BITS_PER_UNIT);
@@ -8709,7 +8707,7 @@ aarch64_layout_frame (void)
 
   HOST_WIDE_INT const_size, const_below_saved_regs, const_above_fp;
   HOST_WIDE_INT const_saved_regs_size;
-  if (known_eq (frame.saved_regs_size, 0))
+  if (known_eq (saved_regs_size, 0))
     frame.initial_adjust = frame.frame_size;
   else if (frame.frame_size.is_constant (&const_size)
 	   && const_size < max_push_offset
@@ -8722,7 +8720,7 @@ aarch64_layout_frame (void)
       frame.callee_adjust = const_size;
     }
   else if (frame.bytes_below_saved_regs.is_constant (&const_below_saved_regs)
-	   && frame.saved_regs_size.is_constant (&const_saved_regs_size)
+	   && saved_regs_size.is_constant (&const_saved_regs_size)
 	   && const_below_saved_regs + const_saved_regs_size < 512
 	   /* We could handle this case even with data below the saved
 	      registers, provided that that data left us with valid offsets
@@ -8741,8 +8739,7 @@ aarch64_layout_frame (void)
       frame.initial_adjust = frame.frame_size;
     }
   else if (saves_below_hard_fp_p
-	   && known_eq (frame.saved_regs_size,
-			frame.below_hard_fp_saved_regs_size))
+	   && known_eq (saved_regs_size, below_hard_fp_saved_regs_size))
     {
       /* Frame in which all saves are SVE saves:
 
@@ -8764,7 +8761,7 @@ aarch64_layout_frame (void)
 	 [save SVE registers relative to SP]
 	 sub sp, sp, bytes_below_saved_regs  */
       frame.callee_adjust = const_above_fp;
-      frame.sve_callee_adjust = frame.below_hard_fp_saved_regs_size;
+      frame.sve_callee_adjust = below_hard_fp_saved_regs_size;
       frame.final_adjust = frame.bytes_below_saved_regs;
     }
   else
@@ -8779,7 +8776,7 @@ aarch64_layout_frame (void)
 	 [save SVE registers relative to SP]
 	 sub sp, sp, bytes_below_saved_regs  */
       frame.initial_adjust = frame.bytes_above_hard_fp;
-      frame.sve_callee_adjust = frame.below_hard_fp_saved_regs_size;
+      frame.sve_callee_adjust = below_hard_fp_saved_regs_size;
       frame.final_adjust = frame.bytes_below_saved_regs;
     }
 
@@ -9985,17 +9982,17 @@ aarch64_epilogue_uses (int regno)
 	|  local variables              | <-- frame_pointer_rtx
 	|                               |
 	+-------------------------------+
-	|  padding                      | \
-	+-------------------------------+  |
-	|  callee-saved registers       |  | frame.saved_regs_size
-	+-------------------------------+  |
-	|  LR'                          |  |
-	+-------------------------------+  |
-	|  FP'                          |  |
-	+-------------------------------+  |<- hard_frame_pointer_rtx (aligned)
-	|  SVE vector registers         |  | \
-	+-------------------------------+  |  | below_hard_fp_saved_regs_size
-	|  SVE predicate registers      | /  /
+	|  padding                      |
+	+-------------------------------+
+	|  callee-saved registers       |
+	+-------------------------------+
+	|  LR'                          |
+	+-------------------------------+
+	|  FP'                          |
+	+-------------------------------+ <-- hard_frame_pointer_rtx (aligned)
+	|  SVE vector registers         |
+	+-------------------------------+
+	|  SVE predicate registers      |
 	+-------------------------------+
 	|  dynamic allocation           |
 	+-------------------------------+
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 8fcebeb5206..d74e9116fc5 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -776,18 +776,11 @@ struct GTY (()) aarch64_frame
      STACK_BOUNDARY.  */
   HOST_WIDE_INT saved_varargs_size;
 
-  /* The size of the callee-save registers with a slot in REG_OFFSET.  */
-  poly_int64 saved_regs_size;
-
   /* The number of bytes between the bottom of the static frame (the bottom
      of the outgoing arguments) and the bottom of the register save area.
      This value is always a multiple of STACK_BOUNDARY.  */
   poly_int64 bytes_below_saved_regs;
 
-  /* The size of the callee-save registers with a slot in REG_OFFSET that
-     are saved below the hard frame pointer.  */
-  poly_int64 below_hard_fp_saved_regs_size;
-
   /* The number of bytes between the bottom of the static frame (the bottom
      of the outgoing arguments) and the hard frame pointer.  This value is
      always a multiple of STACK_BOUNDARY.  */
-- 
2.25.1

[PATCH 19/19] aarch64: Make stack smash canary protect saved registers

[Richard Sandiford]

AArch64 normally puts the saved registers near the bottom of the frame,
immediately above any dynamic allocations.  But this means that a
stack-smash attack on those dynamic allocations could overwrite the
saved registers without needing to reach as far as the stack smash
canary.

The same thing could also happen for variable-sized arguments that are
passed by value, since those are allocated before a call and popped on
return.

This patch avoids that by putting the locals (and thus the canary) below
the saved registers when stack smash protection is active.

The patch fixes CVE-2023-4039.

gcc/
	* config/aarch64/aarch64.cc (aarch64_save_regs_above_locals_p):
	New function.
	(aarch64_layout_frame): Use it to decide whether locals should
	go above or below the saved registers.
	(aarch64_expand_prologue): Update stack layout comment.
	Emit a stack tie after the final adjustment.

gcc/testsuite/
	* gcc.target/aarch64/stack-protector-8.c: New test.
	* gcc.target/aarch64/stack-protector-9.c: Likewise.
---
 gcc/config/aarch64/aarch64.cc                 | 46 +++++++--
 .../gcc.target/aarch64/stack-protector-8.c    | 95 +++++++++++++++++++
 .../gcc.target/aarch64/stack-protector-9.c    | 33 +++++++
 3 files changed, 168 insertions(+), 6 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-protector-8.c
 create mode 100644 gcc/testsuite/gcc.target/aarch64/stack-protector-9.c

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index 51e57370807..3739a44bfd9 100644
--- a/gcc/config/aarch64/aarch64.cc
+++ b/gcc/config/aarch64/aarch64.cc
@@ -8433,6 +8433,20 @@ aarch64_needs_frame_chain (void)
   return aarch64_use_frame_pointer;
 }
 
+/* Return true if the current function should save registers above
+   the locals area, rather than below it.  */
+
+static bool
+aarch64_save_regs_above_locals_p ()
+{
+  /* When using stack smash protection, make sure that the canary slot
+     comes between the locals and the saved registers.  Otherwise,
+     it would be possible for a carefully sized smash attack to change
+     the saved registers (particularly LR and FP) without reaching the
+     canary.  */
+  return crtl->stack_protect_guard;
+}
+
 /* Mark the registers that need to be saved by the callee and calculate
    the size of the callee-saved registers area and frame record (both FP
    and LR may be omitted).  */
@@ -8444,6 +8458,7 @@ aarch64_layout_frame (void)
   poly_int64 vector_save_size = GET_MODE_SIZE (vector_save_mode);
   bool frame_related_fp_reg_p = false;
   aarch64_frame &frame = cfun->machine->frame;
+  poly_int64 top_of_locals = -1;
 
   frame.emit_frame_chain = aarch64_needs_frame_chain ();
 
@@ -8510,9 +8525,16 @@ aarch64_layout_frame (void)
 	&& !crtl->abi->clobbers_full_reg_p (regno))
       frame.reg_offset[regno] = SLOT_REQUIRED;
 
+  bool regs_at_top_p = aarch64_save_regs_above_locals_p ();
 
   poly_int64 offset = crtl->outgoing_args_size;
   gcc_assert (multiple_p (offset, STACK_BOUNDARY / BITS_PER_UNIT));
+  if (regs_at_top_p)
+    {
+      offset += get_frame_size ();
+      offset = aligned_upper_bound (offset, STACK_BOUNDARY / BITS_PER_UNIT);
+      top_of_locals = offset;
+    }
   frame.bytes_below_saved_regs = offset;
   frame.sve_save_and_probe = INVALID_REGNUM;
 
@@ -8652,15 +8674,18 @@ aarch64_layout_frame (void)
      at expand_prologue.  */
   gcc_assert (crtl->is_leaf || maybe_ne (saved_regs_size, 0));
 
-  offset += get_frame_size ();
-  offset = aligned_upper_bound (offset, STACK_BOUNDARY / BITS_PER_UNIT);
-  auto top_of_locals = offset;
-
+  if (!regs_at_top_p)
+    {
+      offset += get_frame_size ();
+      offset = aligned_upper_bound (offset, STACK_BOUNDARY / BITS_PER_UNIT);
+      top_of_locals = offset;
+    }
   offset += frame.saved_varargs_size;
   gcc_assert (multiple_p (offset, STACK_BOUNDARY / BITS_PER_UNIT));
   frame.frame_size = offset;
 
   frame.bytes_above_hard_fp = frame.frame_size - frame.bytes_below_hard_fp;
+  gcc_assert (known_ge (top_of_locals, 0));
   frame.bytes_above_locals = frame.frame_size - top_of_locals;
 
   frame.initial_adjust = 0;
@@ -9979,10 +10004,10 @@ aarch64_epilogue_uses (int regno)
 	|  for register varargs         |
 	|                               |
 	+-------------------------------+
-	|  local variables              | <-- frame_pointer_rtx
+	|  local variables (1)          | <-- frame_pointer_rtx
 	|                               |
 	+-------------------------------+
-	|  padding                      |
+	|  padding (1)                  |
 	+-------------------------------+
 	|  callee-saved registers       |
 	+-------------------------------+
@@ -9994,6 +10019,10 @@ aarch64_epilogue_uses (int regno)
 	+-------------------------------+
 	|  SVE predicate registers      |
 	+-------------------------------+
+	|  local variables (2)          |
+	+-------------------------------+
+	|  padding (2)                  |
+	+-------------------------------+
 	|  dynamic allocation           |
 	+-------------------------------+
 	|  padding                      |
@@ -10003,6 +10032,9 @@ aarch64_epilogue_uses (int regno)
 	+-------------------------------+
 	|                               | <-- stack_pointer_rtx (aligned)
 
+   The regions marked (1) and (2) are mutually exclusive.  (2) is used
+   when aarch64_save_regs_above_locals_p is true.
+
    Dynamic stack allocations via alloca() decrease stack_pointer_rtx
    but leave frame_pointer_rtx and hard_frame_pointer_rtx
    unchanged.
@@ -10198,6 +10230,8 @@ aarch64_expand_prologue (void)
   gcc_assert (known_eq (bytes_below_sp, final_adjust));
   aarch64_allocate_and_probe_stack_space (tmp1_rtx, tmp0_rtx, final_adjust,
 					  !frame_pointer_needed, true);
+  if (emit_frame_chain && maybe_ne (final_adjust, 0))
+    aarch64_emit_stack_tie (hard_frame_pointer_rtx);
 }
 
 /* Return TRUE if we can use a simple_return insn.
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-protector-8.c b/gcc/testsuite/gcc.target/aarch64/stack-protector-8.c
new file mode 100644
index 00000000000..e71d820e365
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-protector-8.c
@@ -0,0 +1,95 @@
+/* { dg-options " -O -fstack-protector-strong -mstack-protector-guard=sysreg -mstack-protector-guard-reg=tpidr2_el0 -mstack-protector-guard-offset=16" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+void g(void *);
+__SVBool_t *h(void *);
+
+/*
+** test1:
+**	sub	sp, sp, #288
+**	stp	x29, x30, \[sp, #?272\]
+**	add	x29, sp, #?272
+**	mrs	(x[0-9]+), tpidr2_el0
+**	ldr	(x[0-9]+), \[\1, #?16\]
+**	str	\2, \[sp, #?264\]
+**	mov	\2, #?0
+**	add	x0, sp, #?8
+**	bl	g
+**	...
+**	mrs	.*
+**	...
+**	bne	.*
+**	...
+**	ldp	x29, x30, \[sp, #?272\]
+**	add	sp, sp, #?288
+**	ret
+**	bl	__stack_chk_fail
+*/
+int test1() {
+  int y[0x40];
+  g(y);
+  return 1;
+}
+
+/*
+** test2:
+**	stp	x29, x30, \[sp, #?-16\]!
+**	mov	x29, sp
+**	sub	sp, sp, #1040
+**	mrs	(x[0-9]+), tpidr2_el0
+**	ldr	(x[0-9]+), \[\1, #?16\]
+**	str	\2, \[sp, #?1032\]
+**	mov	\2, #?0
+**	add	x0, sp, #?8
+**	bl	g
+**	...
+**	mrs	.*
+**	...
+**	bne	.*
+**	...
+**	add	sp, sp, #?1040
+**	ldp	x29, x30, \[sp\], #?16
+**	ret
+**	bl	__stack_chk_fail
+*/
+int test2() {
+  int y[0x100];
+  g(y);
+  return 1;
+}
+
+#pragma GCC target "+sve"
+
+/*
+** test3:
+**	stp	x29, x30, \[sp, #?-16\]!
+**	mov	x29, sp
+**	addvl	sp, sp, #-18
+**	...
+**	str	p4, \[sp\]
+**	...
+**	sub	sp, sp, #272
+**	mrs	(x[0-9]+), tpidr2_el0
+**	ldr	(x[0-9]+), \[\1, #?16\]
+**	str	\2, \[sp, #?264\]
+**	mov	\2, #?0
+**	add	x0, sp, #?8
+**	bl	h
+**	...
+**	mrs	.*
+**	...
+**	bne	.*
+**	...
+**	add	sp, sp, #?272
+**	...
+**	ldr	p4, \[sp\]
+**	...
+**	addvl	sp, sp, #18
+**	ldp	x29, x30, \[sp\], #?16
+**	ret
+**	bl	__stack_chk_fail
+*/
+__SVBool_t test3() {
+  int y[0x40];
+  return *h(y);
+}
diff --git a/gcc/testsuite/gcc.target/aarch64/stack-protector-9.c b/gcc/testsuite/gcc.target/aarch64/stack-protector-9.c
new file mode 100644
index 00000000000..58f322aa480
--- /dev/null
+++ b/gcc/testsuite/gcc.target/aarch64/stack-protector-9.c
@@ -0,0 +1,33 @@
+/* { dg-options "-O2 -mcpu=neoverse-v1 -fstack-protector-all" } */
+/* { dg-final { check-function-bodies "**" "" } } */
+
+/*
+** main:
+**	...
+**	stp	x29, x30, \[sp, #?-[0-9]+\]!
+**	...
+**	sub	sp, sp, #[0-9]+
+**	...
+**	str	x[0-9]+, \[x29, #?-8\]
+**	...
+*/
+int f(const char *);
+void g(void *);
+int main(int argc, char* argv[])
+{
+  int a;
+  int b;
+  char c[2+f(argv[1])];
+  int d[0x100];
+  char y;
+
+  y=42; a=4; b=10;
+  c[0] = 'h'; c[1] = '\0';
+
+  c[f(argv[2])] = '\0';
+
+  __builtin_printf("%d %d\n%s\n", a, b, c);
+  g(d);
+
+  return 0;
+}
-- 
2.25.1

Re: [PATCH 00/19] aarch64: Fix -fstack-protector issue

[Siddhesh Poyarekar]

On 2023-09-12 11:25, Richard Sandiford via Gcc-patches wrote:
> This series of patches fixes deficiencies in GCC's -fstack-protector
> implementation for AArch64 when using dynamically allocated stack space.
> This is CVE-2023-4039.  See:
> 

While this is a legitimate missed hardening, I'm not sure if this 
qualifies as a CVE-worthy vulnerability since correct programs won't 
actually be exploitable due to this.  This is essentially the kind of 
thing that the "Security features implemented in GCC" section in the 
proposed security policy[1] describes.

Thanks,
Sid

[1] 
https://inbox.sourceware.org/gcc-patches/ba133293-a7e8-8fe4-e1ba-7129b9e103f7@gotplt.org/