From c296146c058c87e9ed53001b6a3988519dbbb6a5 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Tue, 18 Sep 2018 23:51:38 -0700 Subject: arm64/kernel: jump_label: Switch to relative references On a randomly chosen distro kernel build for arm64, vmlinux.o shows the following sections, containing jump label entries, and the associated RELA relocation records, respectively: ... [38088] __jump_table PROGBITS 0000000000000000 00e19f30 000000000002ea10 0000000000000000 WA 0 0 8 [38089] .rela__jump_table RELA 0000000000000000 01fd8bb0 000000000008be30 0000000000000018 I 38178 38088 8 ... In other words, we have 190 KB worth of 'struct jump_entry' instances, and 573 KB worth of RELA entries to relocate each entry's code, target and key members. This means the RELA section occupies 10% of the .init segment, and the two sections combined represent 5% of vmlinux's entire memory footprint. So let's switch from 64-bit absolute references to 32-bit relative references for the code and target field, and a 64-bit relative reference for the 'key' field (which may reside in another module or the core kernel, which may be more than 4 GB way on arm64 when running with KASLR enable): this reduces the size of the __jump_table by 33%, and gets rid of the RELA section entirely. Signed-off-by: Ard Biesheuvel Signed-off-by: Thomas Gleixner Acked-by: Will Deacon Acked-by: Peter Zijlstra (Intel) Cc: linux-arm-kernel@lists.infradead.org Cc: linux-s390@vger.kernel.org Cc: Arnd Bergmann Cc: Heiko Carstens Cc: Kees Cook Cc: Catalin Marinas Cc: Steven Rostedt Cc: Martin Schwidefsky Cc: Jessica Yu Link: https://lkml.kernel.org/r/20180919065144.25010-4-ard.biesheuvel@linaro.org --- arch/arm64/include/asm/jump_label.h | 38 ++++++++++++++++++------------------- 1 file changed, 18 insertions(+), 20 deletions(-) (limited to 'arch/arm64/include/asm') diff --git a/arch/arm64/include/asm/jump_label.h b/arch/arm64/include/asm/jump_label.h index 7e2b3e360086..472023498d71 100644 --- a/arch/arm64/include/asm/jump_label.h +++ b/arch/arm64/include/asm/jump_label.h @@ -26,13 +26,16 @@ #define JUMP_LABEL_NOP_SIZE AARCH64_INSN_SIZE -static __always_inline bool arch_static_branch(struct static_key *key, bool branch) +static __always_inline bool arch_static_branch(struct static_key *key, + bool branch) { - asm_volatile_goto("1: nop\n\t" - ".pushsection __jump_table, \"aw\"\n\t" - ".align 3\n\t" - ".quad 1b, %l[l_yes], %c0\n\t" - ".popsection\n\t" + asm_volatile_goto( + "1: nop \n\t" + " .pushsection __jump_table, \"aw\" \n\t" + " .align 3 \n\t" + " .long 1b - ., %l[l_yes] - . \n\t" + " .quad %c0 - . \n\t" + " .popsection \n\t" : : "i"(&((char *)key)[branch]) : : l_yes); return false; @@ -40,13 +43,16 @@ l_yes: return true; } -static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch) +static __always_inline bool arch_static_branch_jump(struct static_key *key, + bool branch) { - asm_volatile_goto("1: b %l[l_yes]\n\t" - ".pushsection __jump_table, \"aw\"\n\t" - ".align 3\n\t" - ".quad 1b, %l[l_yes], %c0\n\t" - ".popsection\n\t" + asm_volatile_goto( + "1: b %l[l_yes] \n\t" + " .pushsection __jump_table, \"aw\" \n\t" + " .align 3 \n\t" + " .long 1b - ., %l[l_yes] - . \n\t" + " .quad %c0 - . \n\t" + " .popsection \n\t" : : "i"(&((char *)key)[branch]) : : l_yes); return false; @@ -54,13 +60,5 @@ l_yes: return true; } -typedef u64 jump_label_t; - -struct jump_entry { - jump_label_t code; - jump_label_t target; - jump_label_t key; -}; - #endif /* __ASSEMBLY__ */ #endif /* __ASM_JUMP_LABEL_H */ -- cgit v1.2.3