linux-kernel - [PATCH] MIPS: Stop using dla in 32 bit kernels

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Date:	Thu, 4 Feb 2016 14:31:57 +0000
From:	Paul Burton <paul.burton@...tec.com>
To:	<linux-mips@...ux-mips.org>
CC:	Paul Burton <paul.burton@...tec.com>,
	<linux-kernel@...r.kernel.org>,
	James Hogan <james.hogan@...tec.com>,
	Markos Chandras <markos.chandras@...tec.com>,
	Ralf Baechle <ralf@...ux-mips.org>
Subject: [PATCH] MIPS: Stop using dla in 32 bit kernels

The instruction_hazard macro made use of the dla pseudo-instruction even
for 32 bit kernels. Although it surrounded that use with ".set mips64rX"
that isn't sufficient to avoid warnings when built with -mabi=32, as
CONFIG_32BIT=y kernels are:

      CC      arch/mips/mm/c-r4k.o
    {standard input}: Assembler messages:
    {standard input}:4105: Warning: dla used to load 32-bit register;
        recommend using la instead
    {standard input}:4129: Warning: dla used to load 32-bit register;
        recommend using la instead

Avoid this by instead making use of the PTR_LA macro which defines the
appropriate variant of the "la" instruction to use.

Tested with Codescape GNU Tools 2015.06-05 for MIPS IMG Linux, which
includes binutils 2.24.90 & gcc 4.9.2.

Signed-off-by: Paul Burton <paul.burton@...tec.com>
---

 arch/mips/include/asm/hazards.h | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/arch/mips/include/asm/hazards.h b/arch/mips/include/asm/hazards.h
index 7b99efd..ffe2aaa 100644
--- a/arch/mips/include/asm/hazards.h
+++ b/arch/mips/include/asm/hazards.h
@@ -11,6 +11,7 @@
 #define _ASM_HAZARDS_H
 
 #include <linux/stringify.h>
+#include <asm/asm.h>
 #include <asm/compiler.h>
 
 #define ___ssnop							\
@@ -54,22 +55,16 @@
 
 /*
  * gcc has a tradition of misscompiling the previous construct using the
- * address of a label as argument to inline assembler.	Gas otoh has the
- * annoying difference between la and dla which are only usable for 32-bit
- * rsp. 64-bit code, so can't be used without conditional compilation.
- * The alterantive is switching the assembler to 64-bit code which happens
- * to work right even for 32-bit code ...
+ * address of a label as argument to inline assembler.
  */
 #define instruction_hazard()						\
 do {									\
 	unsigned long tmp;						\
 									\
 	__asm__ __volatile__(						\
-	"	.set "MIPS_ISA_LEVEL"				\n"	\
-	"	dla	%0, 1f					\n"	\
-	"	jr.hb	%0					\n"	\
-	"	.set	mips0					\n"	\
-	"1:							\n"	\
+	__stringify(PTR_LA) "	%0, 1f\n\t"				\
+	"jr.hb	%0\n\t"							\
+	"1:"								\
 	: "=r" (tmp));							\
 } while (0)
 
-- 
2.7.0