Commit e7bf1ba9 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

jump_label, x86: Emit short JMP 



Now that we can patch short JMP/NOP, allow the compiler/assembler to
emit short JMP instructions.

There is no way to have the assembler emit short NOPs based on the
potential displacement, so leave those long for now.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210506194157.967034497@infradead.org
parent 5af0ea29

arch/x86/include/asm/jump_label.h

+1 −2
Original line number Original line Diff line number Diff line
@@ -35,8 +35,7 @@ static __always_inline bool arch_static_branch(struct static_key * const key, co 
static __always_inline bool arch_static_branch_jump(struct static_key * const key, const bool branch)

static __always_inline bool arch_static_branch_jump(struct static_key * const key, const bool branch)

{

{

	asm_volatile_goto("1:"

	asm_volatile_goto("1:"

		".byte 0xe9 \n\t"

		"jmp %l[l_yes]\n\t"

		".long %l[l_yes] - (. + 4) \n\t"

		JUMP_TABLE_ENTRY

		JUMP_TABLE_ENTRY

		: :  "i" (key), "i" (branch) : : l_yes);

		: :  "i" (key), "i" (branch) : : l_yes);

arch/x86/kernel/jump_label.c

+7 −1
Original line number Original line Diff line number Diff line
@@ -15,12 +15,18 @@ 
#include <asm/kprobes.h>

#include <asm/kprobes.h>

#include <asm/alternative.h>

#include <asm/alternative.h>

#include <asm/text-patching.h>

#include <asm/text-patching.h>

#include <asm/insn.h>





#define JUMP_LABEL_NOP_SIZE	JMP32_INSN_SIZE

#define JUMP_LABEL_NOP_SIZE	JMP32_INSN_SIZE





int arch_jump_entry_size(struct jump_entry *entry)

int arch_jump_entry_size(struct jump_entry *entry)

{

{

	return JMP32_INSN_SIZE;

	struct insn insn = {};



	insn_decode_kernel(&insn, (void *)jump_entry_code(entry));

	BUG_ON(insn.length != 2 && insn.length != 5);



	return insn.length;

}

}





struct jump_label_patch {

struct jump_label_patch {