forked from luck/tmp_suning_uos_patched
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>
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@ -3,18 +3,23 @@
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#ifdef __KERNEL__
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#include <linux/stringify.h>
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#include <linux/types.h>
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#include <asm/nops.h>
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#include <asm/asm.h>
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#define JUMP_LABEL_NOP_SIZE 5
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#define STATIC_KEY_INITIAL_NOP ".byte 0xe9 \n\t .long 0\n\t"
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#ifdef CONFIG_X86_64
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# define STATIC_KEY_INIT_NOP P6_NOP5_ATOMIC
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#else
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# define STATIC_KEY_INIT_NOP GENERIC_NOP5_ATOMIC
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#endif
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static __always_inline bool arch_static_branch(struct static_key *key)
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{
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asm goto("1:"
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STATIC_KEY_INITIAL_NOP
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".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
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".pushsection __jump_table, \"aw\" \n\t"
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_ASM_ALIGN "\n\t"
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_ASM_PTR "1b, %l[l_yes], %c0 \n\t"
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