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/kernel/jump_label.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'arch/arm64/kernel') diff --git a/arch/arm64/kernel/jump_label.c b/arch/arm64/kernel/jump_label.c index e0756416e567..646b9562ee64 100644 --- a/arch/arm64/kernel/jump_label.c +++ b/arch/arm64/kernel/jump_label.c @@ -25,12 +25,12 @@ void arch_jump_label_transform(struct jump_entry *entry, enum jump_label_type type) { - void *addr = (void *)entry->code; + void *addr = (void *)jump_entry_code(entry); u32 insn; if (type == JUMP_LABEL_JMP) { - insn = aarch64_insn_gen_branch_imm(entry->code, - entry->target, + insn = aarch64_insn_gen_branch_imm(jump_entry_code(entry), + jump_entry_target(entry), AARCH64_INSN_BRANCH_NOLINK); } else { insn = aarch64_insn_gen_nop(); -- cgit