From 5b06d7f3a7cb1a01c1665872109d040e0a72c165 Mon Sep 17 00:00:00 2001
From: Evian-Zhang <evianzhang1999@163.com>
Date: Fri, 9 Aug 2024 15:58:50 +0800
Subject: [PATCH] Force 5-byte JMP in x86 and x86-64

---
 src/arch/x86.rs    | 7 ++++---
 src/arch/x86_64.rs | 3 ++-
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/arch/x86.rs b/src/arch/x86.rs
index 16bc9ae..e1c4bb1 100644
--- a/src/arch/x86.rs
+++ b/src/arch/x86.rs
@@ -43,7 +43,8 @@ macro_rules! arch_static_key_init_nop_asm_template {
     };
 }
 
-// The `0x90,0x90,0x90` are three NOPs, which is to make sure the `jmp {0}` is at least 5 bytes long.
+// Here we do not use `jmp {0}` because it may be compiled into a 3-byte jmp instead of 5 byte.
+// See https://stackoverflow.com/q/74771372/10005095
 #[doc(hidden)]
 #[macro_export]
 macro_rules! arch_static_key_init_jmp_asm_template {
@@ -51,8 +52,8 @@ macro_rules! arch_static_key_init_jmp_asm_template {
         ::core::concat!(
             r#"
             2:
-                jmp {0}
-            .byte 0x90,0x90,0x90
+            .byte 0xe9
+            .long ({0} - 4) - .
             .pushsection "#,
             $crate::os_static_key_sec_name_attr!(),
             r#"
diff --git a/src/arch/x86_64.rs b/src/arch/x86_64.rs
index 47e6966..c4ea629 100644
--- a/src/arch/x86_64.rs
+++ b/src/arch/x86_64.rs
@@ -43,7 +43,8 @@ macro_rules! arch_static_key_init_nop_asm_template {
     };
 }
 
-// The `0x90,0x90,0x90` are three NOPs, which is to make sure the `jmp {0}` is at least 5 bytes long.
+// Here we do not use `jmp {0}` because it may be compiled into a 3-byte jmp instead of 5 byte.
+// See https://stackoverflow.com/q/74771372/10005095
 #[doc(hidden)]
 #[macro_export]
 macro_rules! arch_static_key_init_jmp_asm_template {