Messages in this thread Patch in this message | | | Date | Sat, 28 Jan 2012 11:09:26 -0500 | From | Steven Rostedt <> | Subject | [PATCH 1/5 v2] x86/jump-label: Use best default nops for inital jump label calls |
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From: Steven Rostedt <srostedt@redhat.com>
As specified by H. Peter Anvin, the best nops for x86 without knowing the running computer is:
32bit: 0x3e, 0x8d, 0x74, 0x26, 0x00 also known as GENERIC_NOP5_ATOMIC
64bit: 0x0f, 0x1f, 0x44, 0x00, 0x00 also known as P6_NOP5_ATOMIC
Currently the default nop that is used by jump label is:
0xe9 0x00 0x00 0x00 0x00
Which is really a 5byte jump to the next position.
It's better to use a real nop than a jmp.
Cc: H. Peter Anvin <hpa@linux.intel.com> Cc: Jason Baron <jbaron@redhat.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> --- arch/x86/include/asm/jump_label.h | 9 +++++++-- 1 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h index a32b18c..7082743 100644 --- a/arch/x86/include/asm/jump_label.h +++ b/arch/x86/include/asm/jump_label.h @@ -3,18 +3,23 @@ #ifdef __KERNEL__ +#include <linux/stringify.h> #include <linux/types.h> #include <asm/nops.h> #include <asm/asm.h> #define JUMP_LABEL_NOP_SIZE 5 -#define JUMP_LABEL_INITIAL_NOP ".byte 0xe9 \n\t .long 0\n\t" +#ifdef CONFIG_X86_64 +# define JUMP_LABEL_INIT_NOP P6_NOP5_ATOMIC +#else +# define JUMP_LABEL_INIT_NOP GENERIC_NOP5_ATOMIC +#endif static __always_inline bool arch_static_branch(struct jump_label_key *key) { asm goto("1:" - JUMP_LABEL_INITIAL_NOP + ".byte " __stringify(JUMP_LABEL_INIT_NOP) "\n\t" ".pushsection __jump_table, \"aw\" \n\t" _ASM_ALIGN "\n\t" _ASM_PTR "1b, %l[l_yes], %c0 \n\t" -- 1.7.8.3
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