[gcc r14-3895] aarch64: Tweak stack clash boundary condition

[gcc r14-3895] aarch64: Tweak stack clash boundary condition

[Richard Sandiford]

https://gcc.gnu.org/g:1785b8077cc03214ebd1db953c870172fcf15966

commit r14-3895-g1785b8077cc03214ebd1db953c870172fcf15966
Author: Richard Sandiford <richard.sandiford@arm.com>
Date:   Tue Sep 12 16:05:10 2023 +0100

    aarch64: Tweak stack clash boundary condition
    
    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.

Diff:
---
 gcc/config/aarch64/aarch64.cc                      |  4 +-
 .../gcc.target/aarch64/stack-check-prologue-17.c   | 55 ++++++++++++++++++++++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
index e40ccc7d1cf8..b942bf3de4a9 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 000000000000..0d8a25d73a24
--- /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;
+}