From: Steven Rostedt Have the jump labels add a "jmp" in the assembly instead of a default nop. This will cause the assembler to put in either a 2 byte or 5 byte jmp depending on where the target lable is. Then at compile time, the update_jump_label code will replace the jmps with either 2 or 5 byte nops. On boot up, the code can be examined to see if the jump label uses either a 2 or 5 byte nop and replace it. By allowing the jump labels to be 2 bytes, it speeds up the nops, not only 2 byte nops are faster than 5 byte nops, but also because it saves on cache foot print. text data bss dec hex filename 13403667 3666856 2998272 20068795 13239bb ../nobackup/mxtest/vmlinux-old 13398536 3666856 2998272 20063664 13225b0 ../nobackup/mxtest/vmlinux-new Converting the current v3.2 trace points saved 5,131 bytes. As more places use jump labels, this will have a bigger savings. Signed-off-by: Steven Rostedt --- arch/x86/Kconfig | 1 + arch/x86/include/asm/jump_label.h | 7 ++- arch/x86/kernel/jump_label.c | 88 +++++++++++++++++++++++++++---------- 3 files changed, 73 insertions(+), 23 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index b32ebf9..5dbbee2 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -81,6 +81,7 @@ config X86 select HAVE_USER_RETURN_NOTIFIER select ARCH_BINFMT_ELF_RANDOMIZE_PIE select HAVE_ARCH_JUMP_LABEL + select HAVE_BUILD_TIME_JUMP_LABEL select HAVE_TEXT_POKE_SMP select HAVE_GENERIC_HARDIRQS select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h index 64507f3..615adb4 100644 --- a/arch/x86/include/asm/jump_label.h +++ b/arch/x86/include/asm/jump_label.h @@ -10,6 +10,11 @@ #define JUMP_LABEL_NOP_SIZE 5 +/* + * The STATIC_KEY_INIT_NOP must match the nops used in + * scripts/update_jump_label.c. Otherwise the boot time checks + * will fail and trigger a BUG() on boot up. + */ #ifdef CONFIG_X86_64 # define STATIC_KEY_INIT_NOP P6_NOP5_ATOMIC #else @@ -19,7 +24,7 @@ static __always_inline bool arch_static_branch(struct static_key *key) { asm goto("1:" - ".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t" + "jmp %l[l_yes]\n" ".pushsection __jump_table, \"aw\" \n\t" _ASM_ALIGN "\n\t" _ASM_PTR "1b, %l[l_yes], %c0 \n\t" diff --git a/arch/x86/kernel/jump_label.c b/arch/x86/kernel/jump_label.c index 912a528..1a943aa 100644 --- a/arch/x86/kernel/jump_label.c +++ b/arch/x86/kernel/jump_label.c @@ -16,12 +16,20 @@ #ifdef HAVE_JUMP_LABEL +/* These are the nops added at compile time */ +static const unsigned char nop_short[] = { P6_NOP2 }; +static const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; + union jump_code_union { char code[JUMP_LABEL_NOP_SIZE]; struct { char jump; int offset; - } __attribute__((packed)); + } __packed; + struct { + char jump_short; + char offset_short; + } __packed; }; static void bug_at(unsigned char *ip, int line) @@ -42,19 +50,29 @@ static void __jump_label_transform(struct jump_entry *entry, int init) { union jump_code_union code; + unsigned char nop; + unsigned char op; + unsigned size; + void *ip = (void *)entry->code; const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; - if (type == JUMP_LABEL_ENABLE) { - /* - * We are enabling this jump label. If it is not a nop - * then something must have gone wrong. - */ - if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0)) - bug_at((void *)entry->code, __LINE__); + /* Use probe_kernel_read()? */ + op = *(unsigned char *)ip; + nop = ideal_nops[NOP_ATOMIC5][0]; - code.jump = 0xe9; - code.offset = entry->target - - (entry->code + JUMP_LABEL_NOP_SIZE); + if (type == JUMP_LABEL_ENABLE) { + if (memcmp(ip, nop_short, 2) == 0) { + size = 2; + code.jump_short = 0xeb; + code.offset = entry->target - (entry->code + 2); + /* Check for overflow ? */ + } else if ((!init && memcmp(ip, ideal_nop, 5) == 0) || + (init && memcmp(ip, default_nop, 5) == 0)) { + size = JUMP_LABEL_NOP_SIZE; + code.jump = 0xe9; + code.offset = entry->target - (entry->code + size); + } else + bug_at(ip, __LINE__); } else { /* * We are disabling this jump label. If it is not what @@ -63,20 +81,48 @@ static void __jump_label_transform(struct jump_entry *entry, * are converting the default nop to the ideal nop. */ if (init) { - const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; - if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0)) - bug_at((void *)entry->code, __LINE__); - } else { + /* Ignore short nops, we do not change them */ + if (memcmp(ip, nop_short, 2) == 0) + return; + + /* We are initializing from the default nop */ + if (unlikely(memcmp(ip, default_nop, 5) != 0)) + bug_at(ip, __LINE__); + + /* Set to the ideal nop */ + size = JUMP_LABEL_NOP_SIZE; + memcpy(&code, ideal_nops[NOP_ATOMIC5], size); + + } else if (op == 0xe9) { + /* Replace a 5 byte jmp */ + + /* Make sure this is what we expected it to be */ code.jump = 0xe9; code.offset = entry->target - (entry->code + JUMP_LABEL_NOP_SIZE); - if (unlikely(memcmp((void *)entry->code, &code, 5) != 0)) - bug_at((void *)entry->code, __LINE__); - } - memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE); + + if (unlikely(memcmp(ip, &code, 5) != 0)) + bug_at(ip, __LINE__); + + size = JUMP_LABEL_NOP_SIZE; + memcpy(&code, ideal_nops[NOP_ATOMIC5], size); + } else if (op == 0xeb) { + /* Replace a 2 byte jmp */ + + /* Had better be a 2 byte jmp */ + code.jump_short = 0xeb; + code.offset = entry->target - (entry->code + 2); + if (unlikely(memcmp(ip, &code, 2) != 0)) + bug_at(ip, __LINE__); + + size = 2; + memcpy(&code, nop_short, size); + } else + /* The code was not what we expected! */ + bug_at(ip, __LINE__); } - (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE); + (*poker)(ip, &code, size); } void arch_jump_label_transform(struct jump_entry *entry, @@ -106,7 +152,6 @@ __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, * If it is not, then we need to update the nop to the ideal nop. */ if (jlstate == JL_STATE_START) { - const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; if (memcmp(ideal_nop, default_nop, 5) != 0) @@ -117,5 +162,4 @@ __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, if (jlstate == JL_STATE_UPDATE) __jump_label_transform(entry, type, text_poke_early, 1); } - #endif -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/