From cbce34af0a3dae454fb557ac9f168feac692bc7f Mon Sep 17 00:00:00 2001
From: Julian Seward <jseward@acm.org>
Date: Thu, 12 Nov 2020 17:01:30 +0100
Subject: [PATCH] aarch64/inst/unwind.rs: handle zero-length prologues
 correctly.

---
 cranelift/codegen/src/isa/aarch64/inst/unwind.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/cranelift/codegen/src/isa/aarch64/inst/unwind.rs b/cranelift/codegen/src/isa/aarch64/inst/unwind.rs
index 265dd3fb60ce..ff6634ad47b6 100644
--- a/cranelift/codegen/src/isa/aarch64/inst/unwind.rs
+++ b/cranelift/codegen/src/isa/aarch64/inst/unwind.rs
@@ -102,7 +102,12 @@ impl UnwindInfoGenerator<Inst> for AArch64UnwindInfo {
 
         // TODO epilogues
 
-        let prologue_size = context.insts_layout[context.prologue.end as usize - 1];
+        let prologue_size = if context.prologue.is_empty() {
+            0
+        } else {
+            context.insts_layout[context.prologue.end as usize - 1]
+        };
+
         Ok(Some(UnwindInfo {
             prologue_size,
             prologue_unwind_codes: codes,