From 15b7a087471533086df538bc1a21b475f3ef032e Mon Sep 17 00:00:00 2001
From: Mads Marquart <mads@marquart.dk>
Date: Sat, 30 Jul 2022 05:11:00 +0200
Subject: [PATCH] Fix unwinding when debug assertions are enabled

This came up on armv7-apple-ios when using -Zbuild-std
---
 library/panic_unwind/src/gcc.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/library/panic_unwind/src/gcc.rs b/library/panic_unwind/src/gcc.rs
index 057e47bfdd18a..a596592311a64 100644
--- a/library/panic_unwind/src/gcc.rs
+++ b/library/panic_unwind/src/gcc.rs
@@ -306,7 +306,9 @@ unsafe fn find_eh_action(context: *mut uw::_Unwind_Context) -> Result<EHAction,
     let eh_context = EHContext {
         // The return address points 1 byte past the call instruction,
         // which could be in the next IP range in LSDA range table.
-        ip: if ip_before_instr != 0 { ip } else { ip - 1 },
+        //
+        // `ip = -1` has special meaning, so use wrapping sub to allow for that
+        ip: if ip_before_instr != 0 { ip } else { ip.wrapping_sub(1) },
         func_start: uw::_Unwind_GetRegionStart(context),
         get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
         get_data_start: &|| uw::_Unwind_GetDataRelBase(context),