linux-kernel - [PATCH 1/2] compiler.h: Avoid using inline asm operand modifiers

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Date:   Wed, 19 May 2021 15:03:08 +0200
From:   Vasily Gorbik <gor@...ux.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Miroslav Benes <mbenes@...e.cz>, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] compiler.h: Avoid using inline asm operand modifiers

The expansion of annotate_reachable/annotate_unreachable on s390 will
result in a compiler error if the __COUNTER__ value is high enough.
For example with "i" (154) the "%c0" operand of annotate_reachable
will be expanded to -102:

        -102:
        .pushsection .discard.reachable
        .long -102b - .
        .popsection

This is a quirk of the gcc backend for s390, it interprets the %c0
as a signed byte value. Avoid using operand modifiers in this case
by simply converting __COUNTER__ to string, with the same result,
but in an arch assembler independent way.

Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
---
 include/linux/compiler.h | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index df5b405e6305..77047904cf70 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -115,18 +115,24 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
  * The __COUNTER__ based labels are a hack to make each instance of the macros
  * unique, to convince GCC not to merge duplicate inline asm statements.
  */
-#define annotate_reachable() ({						\
-	asm volatile("%c0:\n\t"						\
+#define __stringify_label(n) #n
+
+#define __annotate_reachable(c) ({					\
+	asm volatile(__stringify_label(c) ":\n\t"			\
 		     ".pushsection .discard.reachable\n\t"		\
-		     ".long %c0b - .\n\t"				\
-		     ".popsection\n\t" : : "i" (__COUNTER__));		\
+		     ".long " __stringify_label(c) "b - .\n\t"		\
+		     ".popsection\n\t");				\
 })
-#define annotate_unreachable() ({					\
-	asm volatile("%c0:\n\t"						\
+#define annotate_reachable() __annotate_reachable(__COUNTER__)
+
+#define __annotate_unreachable(c) ({					\
+	asm volatile(__stringify_label(c) ":\n\t"			\
 		     ".pushsection .discard.unreachable\n\t"		\
-		     ".long %c0b - .\n\t"				\
-		     ".popsection\n\t" : : "i" (__COUNTER__));		\
+		     ".long " __stringify_label(c) "b - .\n\t"		\
+		     ".popsection\n\t");				\
 })
+#define annotate_unreachable() __annotate_unreachable(__COUNTER__)
+
 #define ASM_UNREACHABLE							\
 	"999:\n\t"							\
 	".pushsection .discard.unreachable\n\t"				\
-- 
2.25.4