[v5] LoongArch: Fix eh_return epilogue for normal returns.

Message ID 20231208100118.344571-1-yangyujie@loongson.cn
State Committed
Commit 4b421728289e6f1caa0dfaa953a11698ab95d37d
Headers
Series [v5] LoongArch: Fix eh_return epilogue for normal returns. |

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Commit Message

Yang Yujie Dec. 8, 2023, 10:01 a.m. UTC
  On LoongArch, the regitsters $r4 - $r7 (EH_RETURN_DATA_REGNO) will be saved
and restored in the function prologue and epilogue if the given function calls
__builtin_eh_return.  This causes the return value to be overwritten on normal
return paths and breaks a rare case of libgcc's _Unwind_RaiseException.

gcc/ChangeLog:

	* config/loongarch/loongarch.cc: Do not restore the saved eh_return
	data registers ($r4-$r7) for a normal return of a function that calls
	__builtin_eh_return elsewhere.
	* config/loongarch/loongarch-protos.h: Same.
	* config/loongarch/loongarch.md: Same.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/eh_return-normal-return.c: New test.
---
 gcc/config/loongarch/loongarch-protos.h       |  2 +-
 gcc/config/loongarch/loongarch.cc             | 34 ++++++++++++-----
 gcc/config/loongarch/loongarch.md             | 23 ++++++++++-
 .../loongarch/eh_return-normal-return.c       | 38 +++++++++++++++++++
 4 files changed, 84 insertions(+), 13 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c
  

Comments

Lulu Cheng Dec. 12, 2023, 2:03 a.m. UTC | #1
Pushed to r14-6440.

在 2023/12/8 下午6:01, Yang Yujie 写道:
> On LoongArch, the regitsters $r4 - $r7 (EH_RETURN_DATA_REGNO) will be saved
> and restored in the function prologue and epilogue if the given function calls
> __builtin_eh_return.  This causes the return value to be overwritten on normal
> return paths and breaks a rare case of libgcc's _Unwind_RaiseException.
>
> gcc/ChangeLog:
>
> 	* config/loongarch/loongarch.cc: Do not restore the saved eh_return
> 	data registers ($r4-$r7) for a normal return of a function that calls
> 	__builtin_eh_return elsewhere.
> 	* config/loongarch/loongarch-protos.h: Same.
> 	* config/loongarch/loongarch.md: Same.
>
> gcc/testsuite/ChangeLog:
>
> 	* gcc.target/loongarch/eh_return-normal-return.c: New test.
> ---
>   gcc/config/loongarch/loongarch-protos.h       |  2 +-
>   gcc/config/loongarch/loongarch.cc             | 34 ++++++++++++-----
>   gcc/config/loongarch/loongarch.md             | 23 ++++++++++-
>   .../loongarch/eh_return-normal-return.c       | 38 +++++++++++++++++++
>   4 files changed, 84 insertions(+), 13 deletions(-)
>   create mode 100644 gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c
>
> diff --git a/gcc/config/loongarch/loongarch-protos.h b/gcc/config/loongarch/loongarch-protos.h
> index cb8fc36b086..af20b5d7132 100644
> --- a/gcc/config/loongarch/loongarch-protos.h
> +++ b/gcc/config/loongarch/loongarch-protos.h
> @@ -60,7 +60,7 @@ enum loongarch_symbol_type {
>   extern rtx loongarch_emit_move (rtx, rtx);
>   extern HOST_WIDE_INT loongarch_initial_elimination_offset (int, int);
>   extern void loongarch_expand_prologue (void);
> -extern void loongarch_expand_epilogue (bool);
> +extern void loongarch_expand_epilogue (int);
>   extern bool loongarch_can_use_return_insn (void);
>   
>   extern bool loongarch_symbolic_constant_p (rtx, enum loongarch_symbol_type *);
> diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
> index 3545e66a10e..1277c0e9f72 100644
> --- a/gcc/config/loongarch/loongarch.cc
> +++ b/gcc/config/loongarch/loongarch.cc
> @@ -1015,7 +1015,8 @@ loongarch_save_restore_reg (machine_mode mode, int regno, HOST_WIDE_INT offset,
>   
>   static void
>   loongarch_for_each_saved_reg (HOST_WIDE_INT sp_offset,
> -			      loongarch_save_restore_fn fn)
> +			      loongarch_save_restore_fn fn,
> +			      bool skip_eh_data_regs_p)
>   {
>     HOST_WIDE_INT offset;
>   
> @@ -1024,7 +1025,14 @@ loongarch_for_each_saved_reg (HOST_WIDE_INT sp_offset,
>     for (int regno = GP_REG_FIRST; regno <= GP_REG_LAST; regno++)
>       if (BITSET_P (cfun->machine->frame.mask, regno - GP_REG_FIRST))
>         {
> -	if (!cfun->machine->reg_is_wrapped_separately[regno])
> +	/* Special care needs to be taken for $r4-$r7 (EH_RETURN_DATA_REGNO)
> +	   when returning normally from a function that calls
> +	   __builtin_eh_return.  In this case, these registers are saved but
> +	   should not be restored, or the return value may be clobbered.  */
> +
> +	if (!(cfun->machine->reg_is_wrapped_separately[regno]
> +	      || (skip_eh_data_regs_p
> +	      && GP_ARG_FIRST <= regno && regno < GP_ARG_FIRST + 4)))
>   	  loongarch_save_restore_reg (word_mode, regno, offset, fn);
>   
>   	offset -= UNITS_PER_WORD;
> @@ -1297,7 +1305,7 @@ loongarch_expand_prologue (void)
>   			    GEN_INT (-step1));
>         RTX_FRAME_RELATED_P (emit_insn (insn)) = 1;
>         size -= step1;
> -      loongarch_for_each_saved_reg (size, loongarch_save_reg);
> +      loongarch_for_each_saved_reg (size, loongarch_save_reg, false);
>       }
>   
>     /* Set up the frame pointer, if we're using one.  */
> @@ -1382,11 +1390,13 @@ loongarch_can_use_return_insn (void)
>     return reload_completed && cfun->machine->frame.total_size == 0;
>   }
>   
> -/* Expand an "epilogue" or "sibcall_epilogue" pattern; SIBCALL_P
> -   says which.  */
> +/* Expand function epilogue using the following insn patterns:
> +   "epilogue"	      (style == NORMAL_RETURN)
> +   "sibcall_epilogue" (style == SIBCALL_RETURN)
> +   "eh_return"	      (style == EXCEPTION_RETURN) */
>   
>   void
> -loongarch_expand_epilogue (bool sibcall_p)
> +loongarch_expand_epilogue (int style)
>   {
>     /* Split the frame into two.  STEP1 is the amount of stack we should
>        deallocate before restoring the registers.  STEP2 is the amount we
> @@ -1403,7 +1413,8 @@ loongarch_expand_epilogue (bool sibcall_p)
>     bool need_barrier_p
>       = (get_frame_size () + cfun->machine->frame.arg_pointer_offset) != 0;
>   
> -  if (!sibcall_p && loongarch_can_use_return_insn ())
> +  /* Handle simple returns.  */
> +  if (style == NORMAL_RETURN && loongarch_can_use_return_insn ())
>       {
>         emit_jump_insn (gen_return ());
>         return;
> @@ -1479,7 +1490,9 @@ loongarch_expand_epilogue (bool sibcall_p)
>   
>     /* Restore the registers.  */
>     loongarch_for_each_saved_reg (frame->total_size - step2,
> -				loongarch_restore_reg);
> +				loongarch_restore_reg,
> +				crtl->calls_eh_return
> +				&& style != EXCEPTION_RETURN);
>   
>     if (need_barrier_p)
>       loongarch_emit_stack_tie ();
> @@ -1500,11 +1513,12 @@ loongarch_expand_epilogue (bool sibcall_p)
>       }
>   
>     /* Add in the __builtin_eh_return stack adjustment.  */
> -  if (crtl->calls_eh_return)
> +  if (crtl->calls_eh_return && style == EXCEPTION_RETURN)
>       emit_insn (gen_add3_insn (stack_pointer_rtx, stack_pointer_rtx,
>   			      EH_RETURN_STACKADJ_RTX));
>   
> -  if (!sibcall_p)
> +  /* Emit return unless doing sibcall.  */
> +  if (style != SIBCALL_RETURN)
>       emit_jump_insn (gen_simple_return_internal (ra));
>   }
>   
> diff --git a/gcc/config/loongarch/loongarch.md b/gcc/config/loongarch/loongarch.md
> index 7a101dd64b7..93b287c7faf 100644
> --- a/gcc/config/loongarch/loongarch.md
> +++ b/gcc/config/loongarch/loongarch.md
> @@ -118,6 +118,11 @@ (define_constants
>      (T1_REGNUM			13)
>      (S0_REGNUM			23)
>   
> +   ;; Return path styles
> +   (NORMAL_RETURN		0)
> +   (SIBCALL_RETURN		1)
> +   (EXCEPTION_RETURN		2)
> +
>      ;; PIC long branch sequences are never longer than 100 bytes.
>      (MAX_PIC_BRANCH_LENGTH	100)
>   ])
> @@ -3197,7 +3202,7 @@ (define_expand "epilogue"
>     [(const_int 2)]
>     ""
>   {
> -  loongarch_expand_epilogue (false);
> +  loongarch_expand_epilogue (NORMAL_RETURN);
>     DONE;
>   })
>   
> @@ -3205,7 +3210,7 @@ (define_expand "sibcall_epilogue"
>     [(const_int 2)]
>     ""
>   {
> -  loongarch_expand_epilogue (true);
> +  loongarch_expand_epilogue (SIBCALL_RETURN);
>     DONE;
>   })
>   
> @@ -3262,6 +3267,20 @@ (define_expand "eh_return"
>       emit_insn (gen_eh_set_ra_di (operands[0]));
>     else
>       emit_insn (gen_eh_set_ra_si (operands[0]));
> +
> +  emit_jump_insn (gen_eh_return_internal ());
> +  emit_barrier ();
> +  DONE;
> +})
> +
> +(define_insn_and_split "eh_return_internal"
> +  [(eh_return)]
> +  ""
> +  "#"
> +  "epilogue_completed"
> +  [(const_int 0)]
> +{
> +  loongarch_expand_epilogue (EXCEPTION_RETURN);
>     DONE;
>   })
>   
> diff --git a/gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c b/gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c
> new file mode 100644
> index 00000000000..f8f3965f894
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c
> @@ -0,0 +1,38 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2" } */
> +
> +#include <stdlib.h>
> +
> +int foo ()  __attribute__((noinline));
> +int main ();
> +
> +int
> +foo () {
> +
> +  int t;
> +
> +  /* prevent optimization using asm */
> +  asm ("" : "=r" (t) : "0" (-1));
> +  asm ("" : "=r" (t) : "0" (t ? 1 : 0));
> +
> +  if (t == 0)
> +    /* never reached */
> +    __builtin_eh_return (0, __builtin_return_address (0));
> +
> +  else if (t == 1)
> +    /* return here */
> +    return 202312;
> +
> +  else
> +    /* never reached: prevent vrp optimization in main */
> +    return 0;
> +}
> +
> +int
> +main ()
> +{
> +  if (foo() == 202312)
> +    return 0;
> +  else
> +    abort ();
> +}
  

Patch

diff --git a/gcc/config/loongarch/loongarch-protos.h b/gcc/config/loongarch/loongarch-protos.h
index cb8fc36b086..af20b5d7132 100644
--- a/gcc/config/loongarch/loongarch-protos.h
+++ b/gcc/config/loongarch/loongarch-protos.h
@@ -60,7 +60,7 @@  enum loongarch_symbol_type {
 extern rtx loongarch_emit_move (rtx, rtx);
 extern HOST_WIDE_INT loongarch_initial_elimination_offset (int, int);
 extern void loongarch_expand_prologue (void);
-extern void loongarch_expand_epilogue (bool);
+extern void loongarch_expand_epilogue (int);
 extern bool loongarch_can_use_return_insn (void);
 
 extern bool loongarch_symbolic_constant_p (rtx, enum loongarch_symbol_type *);
diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index 3545e66a10e..1277c0e9f72 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -1015,7 +1015,8 @@  loongarch_save_restore_reg (machine_mode mode, int regno, HOST_WIDE_INT offset,
 
 static void
 loongarch_for_each_saved_reg (HOST_WIDE_INT sp_offset,
-			      loongarch_save_restore_fn fn)
+			      loongarch_save_restore_fn fn,
+			      bool skip_eh_data_regs_p)
 {
   HOST_WIDE_INT offset;
 
@@ -1024,7 +1025,14 @@  loongarch_for_each_saved_reg (HOST_WIDE_INT sp_offset,
   for (int regno = GP_REG_FIRST; regno <= GP_REG_LAST; regno++)
     if (BITSET_P (cfun->machine->frame.mask, regno - GP_REG_FIRST))
       {
-	if (!cfun->machine->reg_is_wrapped_separately[regno])
+	/* Special care needs to be taken for $r4-$r7 (EH_RETURN_DATA_REGNO)
+	   when returning normally from a function that calls
+	   __builtin_eh_return.  In this case, these registers are saved but
+	   should not be restored, or the return value may be clobbered.  */
+
+	if (!(cfun->machine->reg_is_wrapped_separately[regno]
+	      || (skip_eh_data_regs_p
+	      && GP_ARG_FIRST <= regno && regno < GP_ARG_FIRST + 4)))
 	  loongarch_save_restore_reg (word_mode, regno, offset, fn);
 
 	offset -= UNITS_PER_WORD;
@@ -1297,7 +1305,7 @@  loongarch_expand_prologue (void)
 			    GEN_INT (-step1));
       RTX_FRAME_RELATED_P (emit_insn (insn)) = 1;
       size -= step1;
-      loongarch_for_each_saved_reg (size, loongarch_save_reg);
+      loongarch_for_each_saved_reg (size, loongarch_save_reg, false);
     }
 
   /* Set up the frame pointer, if we're using one.  */
@@ -1382,11 +1390,13 @@  loongarch_can_use_return_insn (void)
   return reload_completed && cfun->machine->frame.total_size == 0;
 }
 
-/* Expand an "epilogue" or "sibcall_epilogue" pattern; SIBCALL_P
-   says which.  */
+/* Expand function epilogue using the following insn patterns:
+   "epilogue"	      (style == NORMAL_RETURN)
+   "sibcall_epilogue" (style == SIBCALL_RETURN)
+   "eh_return"	      (style == EXCEPTION_RETURN) */
 
 void
-loongarch_expand_epilogue (bool sibcall_p)
+loongarch_expand_epilogue (int style)
 {
   /* Split the frame into two.  STEP1 is the amount of stack we should
      deallocate before restoring the registers.  STEP2 is the amount we
@@ -1403,7 +1413,8 @@  loongarch_expand_epilogue (bool sibcall_p)
   bool need_barrier_p
     = (get_frame_size () + cfun->machine->frame.arg_pointer_offset) != 0;
 
-  if (!sibcall_p && loongarch_can_use_return_insn ())
+  /* Handle simple returns.  */
+  if (style == NORMAL_RETURN && loongarch_can_use_return_insn ())
     {
       emit_jump_insn (gen_return ());
       return;
@@ -1479,7 +1490,9 @@  loongarch_expand_epilogue (bool sibcall_p)
 
   /* Restore the registers.  */
   loongarch_for_each_saved_reg (frame->total_size - step2,
-				loongarch_restore_reg);
+				loongarch_restore_reg,
+				crtl->calls_eh_return
+				&& style != EXCEPTION_RETURN);
 
   if (need_barrier_p)
     loongarch_emit_stack_tie ();
@@ -1500,11 +1513,12 @@  loongarch_expand_epilogue (bool sibcall_p)
     }
 
   /* Add in the __builtin_eh_return stack adjustment.  */
-  if (crtl->calls_eh_return)
+  if (crtl->calls_eh_return && style == EXCEPTION_RETURN)
     emit_insn (gen_add3_insn (stack_pointer_rtx, stack_pointer_rtx,
 			      EH_RETURN_STACKADJ_RTX));
 
-  if (!sibcall_p)
+  /* Emit return unless doing sibcall.  */
+  if (style != SIBCALL_RETURN)
     emit_jump_insn (gen_simple_return_internal (ra));
 }
 
diff --git a/gcc/config/loongarch/loongarch.md b/gcc/config/loongarch/loongarch.md
index 7a101dd64b7..93b287c7faf 100644
--- a/gcc/config/loongarch/loongarch.md
+++ b/gcc/config/loongarch/loongarch.md
@@ -118,6 +118,11 @@  (define_constants
    (T1_REGNUM			13)
    (S0_REGNUM			23)
 
+   ;; Return path styles
+   (NORMAL_RETURN		0)
+   (SIBCALL_RETURN		1)
+   (EXCEPTION_RETURN		2)
+
    ;; PIC long branch sequences are never longer than 100 bytes.
    (MAX_PIC_BRANCH_LENGTH	100)
 ])
@@ -3197,7 +3202,7 @@  (define_expand "epilogue"
   [(const_int 2)]
   ""
 {
-  loongarch_expand_epilogue (false);
+  loongarch_expand_epilogue (NORMAL_RETURN);
   DONE;
 })
 
@@ -3205,7 +3210,7 @@  (define_expand "sibcall_epilogue"
   [(const_int 2)]
   ""
 {
-  loongarch_expand_epilogue (true);
+  loongarch_expand_epilogue (SIBCALL_RETURN);
   DONE;
 })
 
@@ -3262,6 +3267,20 @@  (define_expand "eh_return"
     emit_insn (gen_eh_set_ra_di (operands[0]));
   else
     emit_insn (gen_eh_set_ra_si (operands[0]));
+
+  emit_jump_insn (gen_eh_return_internal ());
+  emit_barrier ();
+  DONE;
+})
+
+(define_insn_and_split "eh_return_internal"
+  [(eh_return)]
+  ""
+  "#"
+  "epilogue_completed"
+  [(const_int 0)]
+{
+  loongarch_expand_epilogue (EXCEPTION_RETURN);
   DONE;
 })
 
diff --git a/gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c b/gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c
new file mode 100644
index 00000000000..f8f3965f894
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/eh_return-normal-return.c
@@ -0,0 +1,38 @@ 
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+#include <stdlib.h>
+
+int foo ()  __attribute__((noinline));
+int main ();
+
+int
+foo () {
+
+  int t;
+
+  /* prevent optimization using asm */
+  asm ("" : "=r" (t) : "0" (-1));
+  asm ("" : "=r" (t) : "0" (t ? 1 : 0));
+
+  if (t == 0)
+    /* never reached */
+    __builtin_eh_return (0, __builtin_return_address (0));
+
+  else if (t == 1)
+    /* return here */
+    return 202312;
+
+  else
+    /* never reached: prevent vrp optimization in main */
+    return 0;
+}
+
+int
+main ()
+{
+  if (foo() == 202312)
+    return 0; 
+  else
+    abort ();
+}