From ffba9b08c471568f1d7e24a0cae889a954cae515 Mon Sep 17 00:00:00 2001
From: Andy Wingo <wingo@igalia.com>
Date: Fri, 19 Jun 2020 16:14:52 +0200
Subject: [PATCH] Fix undefined behavior in ARMv7 assembler

* lightening/arm-cpu.c (rotate_left): Fix the case of rotating by zero,
  which produced undefined behavior.  Many thanks to Andrew
  Gierth (andrew at tao11 riddles org uk) for the debugging and the
  fix.
---
 lightening/arm-cpu.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/lightening/arm-cpu.c b/lightening/arm-cpu.c
index d96d57b2d..39123c730 100644
--- a/lightening/arm-cpu.c
+++ b/lightening/arm-cpu.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2012-2017, 2019  Free Software Foundation, Inc.
+ * Copyright (C) 2012-2017,2019-2020  Free Software Foundation, Inc.
  *
  * This file is part of GNU lightning.
  *
@@ -193,8 +193,15 @@ emit_wide_thumb(jit_state_t *_jit, uint32_t inst)
   emit_u16_with_pool(_jit, inst & 0xffff);
 }
 
-/* from binutils */
-#  define rotate_left(v, n)     (v << n | v >> (32 - n))
+static uint32_t
+rotate_left(uint32_t v, uint32_t n) {
+  if (n == 0) {
+    return v;
+  }
+  ASSERT(n < 32);
+  return (v << n | v >> (32 - n));
+}
+
 static int
 encode_arm_immediate(unsigned int v)
 {