[PATCH 4/5] x86: jump_label: switch to jump_entry accessors
From: peterz@infradead.org (Peter Zijlstra)
Date: 2018-06-28 09:11:52
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On Wed, Jun 27, 2018 at 06:06:03PM +0200, Ard Biesheuvel wrote:
In preparation of switching x86 to use place-relative references for the code, target and key members of struct jump_entry, replace direct references to the struct members with invocations of the new accessors. This will allow us to make the switch by modifying the accessors only. Signed-off-by: Ard Biesheuvel <redacted>
That just makes horrible code worse.. can't we do something like so instead?
--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c@@ -42,52 +42,37 @@ static void __jump_label_transform(struc void *(*poker)(void *, const void *, size_t), int init) { - union jump_code_union code; + union jump_code_union jmp = { + { .jump = 0xe9, + .offset = jump_entry_target(entry) - + (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE), } + }; const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; + const unsigned char *expect, *code; + int line; if (type == JUMP_LABEL_JMP) { if (init) { - /* - * Jump label is enabled for the first time. - * So we expect a default_nop... - */ - if (unlikely(memcmp((void *)entry->code, default_nop, 5) - != 0)) - bug_at((void *)entry->code, __LINE__); + expect = default_nop; line = __LINE__; } else { - /* - * ...otherwise expect an ideal_nop. Otherwise - * something went horribly wrong. - */ - if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) - != 0)) - bug_at((void *)entry->code, __LINE__); + expect = ideal_nop; line = __LINE__; } - code.jump = 0xe9; - code.offset = entry->target - - (entry->code + JUMP_LABEL_NOP_SIZE); + code = &jmp.code; } else { - /* - * We are disabling this jump label. If it is not what - * we think it is, then something must have gone wrong. - * If this is the first initialization call, then we - * are converting the default nop to the ideal nop. - */ if (init) { - if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0)) - bug_at((void *)entry->code, __LINE__); + expect = default_nop; line = __LINE__; } else { - 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__); + expect = &jmp.code; line = __LINE__; } - memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE); + + code = ideal_nop; } + if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE)) + bug_at((void *)jump_entry_code(entry), line); + /* * Make text_poke_bp() a default fallback poker. *
@@ -96,11 +81,13 @@ static void __jump_label_transform(struc * always nop being the 'currently valid' instruction * */ - if (poker) - (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE); - else - text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE, - (void *)entry->code + JUMP_LABEL_NOP_SIZE); + if (poker) { + (*poker)((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE); + return; + } + + text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE, + (void *)jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE); } void arch_jump_label_transform(struct jump_entry *entry,