https://git.ruby-lang.org/ruby.git/commit/?id=26063d3954

From 26063d39546ccd6d0b9d42defc2ad1bb8d35cc27 Mon Sep 17 00:00:00 2001
From: Alan Wu <XrXr@u...>
Date: Sun, 5 Dec 2021 10:08:19 -0500
Subject: YJIT: Initialize code buffer with PUSH DS

PUSH DS triggers the #UD processor exception in 64-bit mode, which the
OS translates to a SIGILL. Unlike INT3, this triggers the usual crash
reporter, which makes failures easier to notice. When there is a
debugger attached, the PUSH DS pauses execution just like INT3.
---
 yjit_asm.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/yjit_asm.c b/yjit_asm.c
index 98f4a4e5157..3a43c80ef08 100644
--- a/yjit_asm.c
+++ b/yjit_asm.c
@@ -215,10 +215,11 @@ static uint8_t *alloc_exec_mem(uint32_t mem_size) https://github.com/ruby/ruby/blob/trunk/yjit_asm.c#L215
 
     cb_init(cb, mem_block, mem_size);
 
-    // Fill the executable memory with INT3 (0xCC) so that
-    // executing uninitialized memory will fault
+    // Fill the executable memory with PUSH DS (0x1E) so that
+    // executing uninitialized memory will fault with #UD in
+    // 64-bit mode.
     cb_mark_all_writeable(cb);
-    memset(mem_block, 0xCC, mem_size);
+    memset(mem_block, 0x1E, mem_size);
     cb_mark_all_executable(cb);
 
     return mem_block;
-- 
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