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[ARM] Fix PR51643

Message ID 4EF33C1F.9080209@arm.com
State New
Headers show

Commit Message

Richard Earnshaw Dec. 22, 2011, 2:18 p.m. UTC 
The ARM bare-metal configuration of the EABI specifies that an
unresolved weak direct call becomes a NOP rather than faulting; but this
is only supported for the BL instruction.  GCC mishandled this in some
cases by trying to convert such a call into a tail-call, but B
instructions are not covered by the requirement above, which means that
the optimization is unsafe.

Fixed thus:

2011-12-21  Richard Earnshaw  <rearnsha@arm.com>

	PR target/51643
	* arm.c (arm_function_ok_for_sibcall): Don't try to tailcall a
	weak function on bare-metal EABI targets.

2011-12-21  Richard Earnshaw  <rearnsha@arm.com>

	PR target/51643
	* gcc.target/arm/sibcall-2.c: New test.

Comments

Richard Henderson Dec. 22, 2011, 5:06 p.m. UTC | #1 
On 12/22/2011 06:18 AM, Richard Earnshaw wrote:
> +      && lookup_attribute ("weak", DECL_ATTRIBUTES (decl)))

DECL_WEAK (decl)


r~
Richard Earnshaw Dec. 22, 2011, 5:34 p.m. UTC | #2 
On 22/12/11 17:06, Richard Henderson wrote:
> On 12/22/2011 06:18 AM, Richard Earnshaw wrote:
>> +      && lookup_attribute ("weak", DECL_ATTRIBUTES (decl)))
> 
> DECL_WEAK (decl)
> 
> 
> r~
> 

Dur, fixed.

R.
diff mbox

Patch

Index: testsuite/gcc.target/arm/sibcall-2.c
===================================================================
--- testsuite/gcc.target/arm/sibcall-2.c	(revision 0)
+++ testsuite/gcc.target/arm/sibcall-2.c	(revision 0)
@@ -0,0 +1,12 @@ 
+/* { dg-require-effective-target arm_eabi } */
+/* { dg-do compile } */
+/* { dg-options "-O2 -mabi=aapcs" } */
+
+
+extern void __attribute__((weak)) wfunc(void);
+void main(void)
+{
+  wfunc();  /* Must not tail-call.  */
+}
+
+/* { dg-final { scan-assembler-not "b\[\\t \]+wfunc" } } */
Index: config/arm/arm.c
===================================================================
--- config/arm/arm.c	(revision 182620)
+++ config/arm/arm.c	(working copy)
@@ -5250,6 +5250,14 @@  arm_function_ok_for_sibcall (tree decl, 
   if (IS_STACKALIGN (func_type))
     return false;
 
+  /* The AAPCS says that, on bare-metal, calls to unresolved weak
+     references should become a NOP.  Don't convert such calls into
+     sibling calls.  */
+  if (TARGET_AAPCS_BASED
+      && arm_abi == ARM_ABI_AAPCS
+      && lookup_attribute ("weak", DECL_ATTRIBUTES (decl)))
+    return false;
+
   /* Everything else is ok.  */
   return true;
 }