From c51d8ff458e00b34e03b1fd5ac9bb0665c5a516a Mon Sep 17 00:00:00 2001
From: Peter Zhu <peter@peterzhu.ca>
Date: Tue, 24 Sep 2024 13:20:35 -0400
Subject: [PATCH] Fix undefined behavior in String#append_as_bytes

The UNREACHABLE macro calls __builtin_unreachable, which according to
the [GCC docs](https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-_005f_005fbuiltin_005funreachable):

> If control flow reaches the point of the __builtin_unreachable, the
> program is undefined.

But it can reach this point with the following script:

    "123".append_as_bytes("123")

This can crash on some platforms with a `Trace/BPT trap: 5`.
---
 string.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/string.c b/string.c
index 608d5cf7dc..dee17c86a6 100644
--- a/string.c
+++ b/string.c
@@ -3790,6 +3790,7 @@ rb_str_append_as_bytes(int argc, VALUE *argv, VALUE str)
                 if (ENC_CODERANGE(obj) != ENC_CODERANGE_7BIT) {
                     goto clear_cr;
                 }
+                break;
               }
               default:
                 UNREACHABLE;