From ab3257042c26d0cd44793c741e2f89bf38b21fe8 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Thu, 6 May 2021 21:34:05 +0200 Subject: [PATCH] jump_label, x86: Allow short NOPs Now that objtool is able to rewrite jump_label instructions, have the compiler emit a JMP, such that it can decide on the optimal encoding, and set jump_entry::key bit1 to indicate that objtool should rewrite the instruction to a matching NOP. For x86_64-allyesconfig this gives: jl\ NOP JMP short: 22997 124 long: 30874 90 IOW, we save (22997+124) * 3 bytes of kernel text in hotpaths. Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20210506194158.216763632@infradead.org --- arch/x86/include/asm/jump_label.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h index ef819e33cfc1..0449b125d27f 100644 --- a/arch/x86/include/asm/jump_label.h +++ b/arch/x86/include/asm/jump_label.h @@ -20,6 +20,22 @@ _ASM_PTR "%c0 + %c1 - .\n\t" \ ".popsection \n\t" +#ifdef CONFIG_STACK_VALIDATION + +static __always_inline bool arch_static_branch(struct static_key *key, bool branch) +{ + asm_volatile_goto("1:" + "jmp %l[l_yes] # objtool NOPs this \n\t" + JUMP_TABLE_ENTRY + : : "i" (key), "i" (2 | branch) : : l_yes); + + return false; +l_yes: + return true; +} + +#else + static __always_inline bool arch_static_branch(struct static_key * const key, const bool branch) { asm_volatile_goto("1:" @@ -32,6 +48,8 @@ l_yes: return true; } +#endif /* STACK_VALIDATION */ + static __always_inline bool arch_static_branch_jump(struct static_key * const key, const bool branch) { asm_volatile_goto("1:"