From e7bf1ba97afdde75b0ef43e4bdb718bf843613f1 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 6 May 2021 21:34:01 +0200 Subject: [PATCH] jump_label, x86: Emit short JMP 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) Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20210506194157.967034497@infradead.org --- arch/x86/include/asm/jump_label.h | 3 +-- arch/x86/kernel/jump_label.c | 8 +++++++- 2 files changed, 8 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h index d85802a00629..ef819e33cfc1 100644 --- a/arch/x86/include/asm/jump_label.h +++ b/arch/x86/include/asm/jump_label.h @@ -35,8 +35,7 @@ l_yes: 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); diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c index 190d810fa435..a762dc1c615e 100644 --- a/arch/x86/kernel/jump_label.c +++ b/arch/x86/kernel/jump_label.c @@ -15,12 +15,18 @@ #include #include #include +#include #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 {