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[PATCH][SPARC] PR target/80968 Prevent stack loads in return delay slot.


This is an attempt to fix PR target/80968.  This bug has existed
basically forever.

The stack_tie sequence seems to be how other targets deal with this
issue.  I only emit this when alloca is used.  If there are other
conditions that potentially would necessitate such a barrier, just let
me know.

====================
sparc: Fix stack references in return delay slot.

gcc/

	* config/sparc/sparc.md (UNSPEC_TIE): New unspec.
	(stack_tie): New pattern.
	* config/sparc/sparc.c (sparc_emit_stack_tie): New function.
	(sparc_expand_prologue): Call it if function uses alloca.

gcc/testsuite/

	* gcc.target/sparc/sparc-ret-3.c: New test.
---
 gcc/config/sparc/sparc.c                     | 15 ++++++++
 gcc/config/sparc/sparc.md                    | 11 ++++++
 gcc/testsuite/gcc.target/sparc/sparc-ret-3.c | 53 ++++++++++++++++++++++++++++
 3 files changed, 79 insertions(+)
 create mode 100644 gcc/testsuite/gcc.target/sparc/sparc-ret-3.c

diff --git a/gcc/config/sparc/sparc.c b/gcc/config/sparc/sparc.c
index 6dfb269..345bc7f 100644
--- a/gcc/config/sparc/sparc.c
+++ b/gcc/config/sparc/sparc.c
@@ -5784,6 +5784,18 @@ sparc_asm_function_prologue (FILE *file, HOST_WIDE_INT size ATTRIBUTE_UNUSED)
   sparc_output_scratch_registers (file);
 }
 
+/* This ties together stack memory (MEM with an alias set of frame_alias_set)
+   and the change to the stack pointer.  */
+
+static void
+sparc_emit_stack_tie (void)
+{
+  rtx mem = gen_frame_mem (BLKmode,
+			   gen_rtx_REG (Pmode, STACK_POINTER_REGNUM));
+
+  emit_insn (gen_stack_tie (mem));
+}
+
 /* Expand the function epilogue, either normal or part of a sibcall.
    We emit all the instructions except the return or the call.  */
 
@@ -5792,6 +5804,9 @@ sparc_expand_epilogue (bool for_eh)
 {
   HOST_WIDE_INT size = sparc_frame_size;
 
+  if (cfun->calls_alloca)
+    sparc_emit_stack_tie ();
+
   if (sparc_n_global_fp_regs > 0)
     emit_save_or_restore_global_fp_regs (sparc_frame_base_reg,
 				         sparc_frame_base_offset
diff --git a/gcc/config/sparc/sparc.md b/gcc/config/sparc/sparc.md
index 737bdb3..ef00fc5 100644
--- a/gcc/config/sparc/sparc.md
+++ b/gcc/config/sparc/sparc.md
@@ -94,6 +94,8 @@
   UNSPEC_ADDV
   UNSPEC_SUBV
   UNSPEC_NEGV
+
+  UNSPEC_TIE
 ])
 
 (define_c_enum "unspecv" [
@@ -8473,6 +8475,15 @@
   [(set_attr "type" "multi")
    (set_attr "length" "4")])
 
+;; This is used in sparc_expand_epilogue in order to prevent insns
+;; referencing the stack from being placed after the deallocation of
+;; the stack frame.
+(define_insn "stack_tie"
+  [(set (match_operand:BLK 0 "memory_operand" "+m")
+        (unspec:BLK [(match_dup 0)] UNSPEC_TIE))]
+  ""
+  ""
+  [(set_attr "length" "0")])
 
 ;; Vector instructions.
 
diff --git a/gcc/testsuite/gcc.target/sparc/sparc-ret-3.c b/gcc/testsuite/gcc.target/sparc/sparc-ret-3.c
new file mode 100644
index 0000000..7a151f8
--- /dev/null
+++ b/gcc/testsuite/gcc.target/sparc/sparc-ret-3.c
@@ -0,0 +1,53 @@
+/* PR target/80968 */
+/* { dg-do compile } */
+/* { dg-skip-if "no register windows" { *-*-* } { "-mflat" } { "" } } */
+/* { dg-require-effective-target ilp32 } */
+/* { dg-options "-mcpu=ultrasparc -O" } */
+
+/* Make sure references to the stack frame do not slip into the delay slot
+   of a return instruction.  */
+
+struct crypto_shash {
+	unsigned int descsize;
+};
+struct crypto_shash *tfm;
+
+struct shash_desc {
+	struct crypto_shash *tfm;
+	unsigned int flags;
+
+	void *__ctx[] __attribute__((aligned(8)));
+};
+
+static inline unsigned int crypto_shash_descsize(struct crypto_shash *tfm)
+{
+	return tfm->descsize;
+}
+
+static inline void *shash_desc_ctx(struct shash_desc *desc)
+{
+	return desc->__ctx;
+}
+
+#define SHASH_DESC_ON_STACK(shash, ctx)				  \
+	char __##shash##_desc[sizeof(struct shash_desc) +	  \
+			      crypto_shash_descsize(ctx)] __attribute__((aligned(8))); \
+	struct shash_desc *shash = (struct shash_desc *)__##shash##_desc
+
+extern int crypto_shash_update(struct shash_desc *, const void *, unsigned int);
+
+unsigned int bug(unsigned int crc, const void *address, unsigned int length)
+{
+	SHASH_DESC_ON_STACK(shash, tfm);
+	unsigned int *ctx = (unsigned int *)shash_desc_ctx(shash);
+	int err;
+
+	shash->tfm = tfm;
+	shash->flags = 0;
+	*ctx = crc;
+
+	err = crypto_shash_update(shash, address, length);
+
+	return *ctx;
+}
+/* { dg-final { scan-assembler "ld\[ \t\]*\\\[%i5\\+8\\\], %i0\n\[^\n\]*return\[ \t\]*%i7\\+8" } } */
-- 
2.1.2.532.g19b5d50


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