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jump_label, x86: Emit short JMP

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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: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210506194157.967034497@infradead.org
This commit is contained in:
Peter Zijlstra 2021-05-06 21:34:01 +02:00 committed by Ingo Molnar
parent 5af0ea293d
commit e7bf1ba97a
2 changed files with 8 additions and 3 deletions
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3
arch/x86/include/asm/jump_label.h
View File

@ -35,8 +35,7 @@ l_yes:
static __always_inline bool arch_static_branch_jump(struct static_key * const key, const bool branch)
{
asm_volatile_goto("1:"
".byte 0xe9 \n\t"
".long %l[l_yes] - (. + 4) \n\t"
"jmp %l[l_yes]\n\t"
JUMP_TABLE_ENTRY
: : "i" (key), "i" (branch) : : l_yes);

8
arch/x86/kernel/jump_label.c
View File

@ -15,12 +15,18 @@
#include <asm/kprobes.h>
#include <asm/alternative.h>
#include <asm/text-patching.h>
#include <asm/insn.h>
#define JUMP_LABEL_NOP_SIZE JMP32_INSN_SIZE
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 {