| Message ID | 20180627160604.8154-4-ard.biesheuvel@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | add support for relative references in jump tables | expand |
On Wed, Jun 27, 2018 at 06:06:02PM +0200, Ard Biesheuvel wrote: > 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: this reduces the size of the __jump_table by 50%, and gets > rid of the RELA section entirely. > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> > --- > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/jump_label.h | 16 ++++------------ > arch/arm64/kernel/jump_label.c | 6 +++--- > 3 files changed, 8 insertions(+), 15 deletions(-) Looks good, cheers: Acked-by: Will Deacon <will.deacon@arm.com> Will
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 1940c6405d04..d17aa9614e69 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -91,6 +91,7 @@ config ARM64 select HAVE_ARCH_BITREVERSE select HAVE_ARCH_HUGE_VMAP select HAVE_ARCH_JUMP_LABEL + select HAVE_ARCH_JUMP_LABEL_RELATIVE select HAVE_ARCH_KASAN if !(ARM64_16K_PAGES && ARM64_VA_BITS_48) select HAVE_ARCH_KGDB select HAVE_ARCH_MMAP_RND_BITS diff --git a/arch/arm64/include/asm/jump_label.h b/arch/arm64/include/asm/jump_label.h index 1b5e0e843c3a..5e3e31df3805 100644 --- a/arch/arm64/include/asm/jump_label.h +++ b/arch/arm64/include/asm/jump_label.h @@ -30,8 +30,8 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran { asm goto("1: nop\n\t" ".pushsection __jump_table, \"aw\"\n\t" - ".align 3\n\t" - ".quad 1b, %l[l_yes], %c0\n\t" + ".align 2\n\t" + ".long 1b - ., %l[l_yes] - ., %c0 - .\n\t" ".popsection\n\t" : : "i"(&((char *)key)[branch]) : : l_yes); @@ -44,8 +44,8 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool { asm 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" + ".align 2\n\t" + ".long 1b - ., %l[l_yes] - ., %c0 - .\n\t" ".popsection\n\t" : : "i"(&((char *)key)[branch]) : : l_yes); @@ -54,13 +54,5 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool 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 */ diff --git a/arch/arm64/kernel/jump_label.c b/arch/arm64/kernel/jump_label.c index c2dd1ad3e648..903d17023d77 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();
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: this reduces the size of the __jump_table by 50%, and gets rid of the RELA section entirely. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- arch/arm64/Kconfig | 1 + arch/arm64/include/asm/jump_label.h | 16 ++++------------ arch/arm64/kernel/jump_label.c | 6 +++--- 3 files changed, 8 insertions(+), 15 deletions(-) -- 2.11.0