Messages in this thread Patch in this message | | | Date | Thu, 06 May 2021 21:34:01 +0200 | From | Peter Zijlstra <> | Subject | [PATCH 09/13] jump_label,x86: Emit short JMP |
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Now that we can patch short JMP/NOP, allow the compiler/assembler to emit short JMP instructions.
There is no way to have the assembler emit short NOPs based on the potential displacement, so leave those long for now.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/x86/include/asm/jump_label.h | 3 +-- arch/x86/kernel/jump_label.c | 8 +++++++- 2 files changed, 8 insertions(+), 3 deletions(-)
--- a/arch/x86/include/asm/jump_label.h +++ b/arch/x86/include/asm/jump_label.h @@ -35,8 +35,7 @@ static __always_inline bool arch_static_ static __always_inline bool arch_static_branch_jump(struct static_key * const key, const bool branch) { asm_volatile_goto("1:" - ".byte 0xe9 \n\t" - ".long %l[l_yes] - (. + 4) \n\t" + "jmp %l[l_yes]\n\t" JUMP_TABLE_ENTRY : : "i" (key), "i" (branch) : : l_yes); --- a/arch/x86/kernel/jump_label.c +++ b/arch/x86/kernel/jump_label.c @@ -15,12 +15,18 @@ #include <asm/kprobes.h> #include <asm/alternative.h> #include <asm/text-patching.h> +#include <asm/insn.h> #define JUMP_LABEL_NOP_SIZE JMP32_INSN_SIZE int arch_jump_entry_size(struct jump_entry *entry) { - return JMP32_INSN_SIZE; + struct insn insn = {}; + + insn_decode_kernel(&insn, (void *)jump_entry_code(entry)); + BUG_ON(insn.length != 2 && insn.length != 5); + + return insn.length; } struct jump_label_patch {
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