From d420acd816c07c7be31bd19d09cbcb16e5572fa6 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed, 12 Aug 2015 21:04:22 +0200
Subject: [PATCH] jump_label/x86: Work around asm build bug on older/backported
GCCs
Boris reported that gcc version 4.4.4 20100503 (Red Hat
4.4.4-2) fails to build linux-next kernels that have
this fresh commit via the locking tree:
11276d5306b8 ("locking/static_keys: Add a new static_key interface")
The problem appears to be that even though @key and @branch are
compile time constants, it doesn't see the following expression
as an immediate value:
&((char *)key)[branch]
More recent GCCs don't appear to have this problem.
In particular, Red Hat backported the 'asm goto' feature into 4.4,
'normal' 4.4 compilers will not have this feature and thus not
run into this asm.
The workaround is to supply both values to the asm as immediates
and do the addition in asm.
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Reported-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/include/asm/jump_label.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index 28d7a857f9d12..5daeca3d0f9e5 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -22,9 +22,9 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran
".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
".pushsection __jump_table, \"aw\" \n\t"
_ASM_ALIGN "\n\t"
- _ASM_PTR "1b, %l[l_yes], %c0 \n\t"
+ _ASM_PTR "1b, %l[l_yes], %c0 + %c1 \n\t"
".popsection \n\t"
- : : "i" (&((char *)key)[branch]) : : l_yes);
+ : : "i" (key), "i" (branch) : : l_yes);
return false;
l_yes:
@@ -38,9 +38,9 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool
"2:\n\t"
".pushsection __jump_table, \"aw\" \n\t"
_ASM_ALIGN "\n\t"
- _ASM_PTR "1b, %l[l_yes], %c0 \n\t"
+ _ASM_PTR "1b, %l[l_yes], %c0 + %c1 \n\t"
".popsection \n\t"
- : : "i" (&((char *)key)[branch]) : : l_yes);
+ : : "i" (key), "i" (branch) : : l_yes);
return false;
l_yes:
--
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