[PATCH] ARM: teach __asmeq that r12 and ip are the same register

[Ard Biesheuvel]

The __asmeq macro is used inside inline asm statements to ensure that
register asm variables that explicitly specify a register are mapped
correctly onto those registers when used in inline asm input and output
constraints. However, the string based matching fails to take into account
that 'ip' may also be referred to as 'r12', (e.g., by clang), causing false
negatives.

Fix this by making __asmeq consider the ("ip","r12") and ("r12","ip")
cases specifically.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
Even though clang shouldn't be susceptible to the same bug, there is still
value in retaining these assertions there, so instead of just turning
__asmeq into a nop if __clang__ is defined, let's make it work correctly.

 arch/arm/include/asm/compiler.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/compiler.h b/arch/arm/include/asm/compiler.h
index 8155db2f7fa1..c3a316a59710 100644
--- a/arch/arm/include/asm/compiler.h
+++ b/arch/arm/include/asm/compiler.h
@@ -8,8 +8,11 @@
  * This string is meant to be concatenated with the inline asm string and
  * will cause compilation to stop on mismatch.
  * (for details, see gcc PR 15089)
+ * For compatibility with clang, we have to explicitly take the equivalence
+ * of 'r12' and 'ip into account as well.
  */
-#define __asmeq(x, y)  ".ifnc " x "," y " ; .err ; .endif\n\t"
+#define __asmeq(x, y)  ".ifnc " x "," y " ; .ifnc " x y ",ipr12 ; " \
+	".ifnc " x y ",r12ip ; .err ; .endif ; .endif ; .endif\n\t"
 
 
 #endif /* __ASM_ARM_COMPILER_H */
-- 
1.8.3.2