[PATCH v2] ARM: teach __asmeq that r11 == fp and r12 == ip

[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 'fp' is often referred to as 'r11' and 'ip' is often referred to as
'r12', (e.g., by clang), causing false negatives.

Fix this by making __asmeq consider the ("fp","r11"), ("r11","fp"),
("ip","r12") and ("r12","ip") cases specifically.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
v2:
Added r11 but not r10, as the latter is only referred to as 'sl' in
objdump output, but GCC emitted inline asm substitutes the references
with 'r10' instead. sp/lr/pc are unambiguous between GCC and clang.

Primary purpose of this patch is to fix the incompatibility between clang
and GCC, but the side effect is that it relaxes the requirement imposed on
the programmer to refer to a register by the same name as the compiler does.
If that is seen as a substantial upside by some, we could indeed still decide
to add r10, r13, r14 and r15 (for which no such incompatibility exists) as well.
However, those are not currently used in __asmeq invocations anywhere under
arch/arm

 arch/arm/include/asm/compiler.h | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/compiler.h b/arch/arm/include/asm/compiler.h
index 8155db2f7fa1..29fe85e59439 100644
--- a/arch/arm/include/asm/compiler.h
+++ b/arch/arm/include/asm/compiler.h
@@ -8,8 +8,21 @@
  * 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 specifically take the equivalence
+ * of 'r11' <-> 'fp' and 'r12' <-> '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 ",fpr11; " 		\
+	    ".ifnc " x y ",r11fp; "		\
+	      ".ifnc " x y ",ipr12; " 		\
+	        ".ifnc " x y ",r12ip; "		\
+	          ".err; "			\
+	        ".endif; "			\
+	      ".endif; "			\
+	    ".endif; "				\
+	  ".endif; "				\
+	".endif\n\t"
 
 
 #endif /* __ASM_ARM_COMPILER_H */
-- 
1.8.3.2