From 4bd69a209b90776ea6dfe90d6e3ee9d770a3b16c Mon Sep 17 00:00:00 2001
From: Matt Jacobson <mhjacobson@me.com>
Date: Sat, 22 Oct 2022 04:37:50 -0400
Subject: [PATCH] runtime: fix compile failure from use of _Unwind_Backtrace()
 on FreeBSD

FreeBSD's libunwind situation is complex.  It uses LLVM's libunwind library,
built as part of FreeBSD's libgcc_s.so.  (The latter, despite its name, does not
actually come from gcc in modern FreeBSD.)

However, it *also* uses libcxxrt (not LLVM's libcxxabi).  libcxxrt installs an
<unwind.h> originally from <https://github.com/libunwind/libunwind>.  That
<unwind.h> surrounds its declaration of _Unwind_Backtrace with _GNU_SOURCE
guards.

Therefore: on FreeBSD, define _GNU_SOURCE so that withCurrentBacktraceImpl() can
access _Unwind_Backtrace.

For posterity, a (probably partial) list of the various <unwind.h>s (and how
they relate to this change):

1. gcc provides one as part of its libgcc (FreeBSD does not use gcc and provides
   its own libgcc that does not have an <unwind.h>)
2. LLVM's libunwind provides one (but FreeBSD does not install it)
3. <https://github.com/libunwind/libunwind> provides one (FreeBSD has this one,
   via its libc++, via its libcxxrt)
4. clang provides one (FreeBSD *has* this one, but the header search path for
   C++ source files prefers number 3)
---
 stdlib/public/runtime/Errors.cpp | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/stdlib/public/runtime/Errors.cpp b/stdlib/public/runtime/Errors.cpp
index c3d5b0ff5f81c..e027ec6e72dbe 100644
--- a/stdlib/public/runtime/Errors.cpp
+++ b/stdlib/public/runtime/Errors.cpp
@@ -22,6 +22,22 @@
 #include <mutex>
 #endif
 
+#if defined(__ELF__)
+# if defined(__FreeBSD__) && !defined(_GNU_SOURCE)
+// In order to access _Unwind_Backtrace() from (the non-LLVM, non-GCC)
+// <unwind.h> in FreeBSD, define _GNU_SOURCE around the include.  Do this
+// before including other headers which may in turn include <unwind.h>, which
+// has a header guard.
+#  define _GNU_SOURCE
+#  define _SHOULD_UNDEFINE_GNU_SOURCE
+# endif
+# include <unwind.h>
+# ifdef _SHOULD_UNDEFINE_GNU_SOURCE
+#  undef _GNU_SOURCE
+#  undef _SHOULD_UNDEFINE_GNU_SOURCE
+# endif
+#endif
+
 #include <inttypes.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -56,10 +72,6 @@
 #include <android/log.h>
 #endif
 
-#if defined(__ELF__)
-#include <unwind.h>
-#endif
-
 #include <inttypes.h>
 
 #ifdef SWIFT_HAVE_CRASHREPORTERCLIENT