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| author | Steven Rostedt <srostedt@redhat.com> | 2012-01-27 00:06:45 +0100 |
|---|---|---|
| committer | Steven Rostedt <rostedt@goodmis.org> | 2013-08-07 03:16:33 +0200 |
| commit | c3c7f14a116c24d6fba185c95cd7454f3764f8a9 (patch) | |
| tree | 1766dcc9afbc1a1417c2783a601c7c7973b71eef /arch/x86 | |
| parent | Linux 3.11-rc1 (diff) | |
| download | linux-c3c7f14a116c24d6fba185c95cd7454f3764f8a9.tar.xz linux-c3c7f14a116c24d6fba185c95cd7454f3764f8a9.zip | |
x86/jump-label: Use best default nops for inital jump label calls
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>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | 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 3a16c1483b45..64507f35800c 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 STATIC_KEY_INITIAL_NOP ".byte 0xe9 \n\t .long 0\n\t" +#ifdef CONFIG_X86_64 +# define STATIC_KEY_INIT_NOP P6_NOP5_ATOMIC +#else +# define STATIC_KEY_INIT_NOP GENERIC_NOP5_ATOMIC +#endif static __always_inline bool arch_static_branch(struct static_key *key) { asm goto("1:" - STATIC_KEY_INITIAL_NOP + ".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" |