3.16.68-rc1 review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
commit d420acd816c07c7be31bd19d09cbcb16e5572fa6 upstream.
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 Signed-off-by: Ben Hutchings ben@decadent.org.uk --- arch/x86/include/asm/jump_label.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
--- 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_ ".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_ "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: