From 77ac8927fda49722185dab219365be31daed8872 Mon Sep 17 00:00:00 2001
From: Ed Maste <emaste@FreeBSD.org>
Date: Wed, 21 Dec 2016 14:06:44 +0000
Subject: [PATCH] libunwind: make __{de,}register_frame compatible with libgcc
 API

The libgcc __register_frame and __deregister_frame functions take a
pointer to a set of FDE/CIEs, terminated by an entry where length is 0.

In Apple's libunwind implementation the pointer is taken to be to a
single FDE. I suspect this was just an Apple bug, compensated by Apple-
specific code in LLVM.

See lib/ExecutionEngine/RuntimeDyld/RTDyldMemoryManager.cpp and
http://lists.llvm.org/pipermail/llvm-dev/2013-April/061737.html
for more detail.

This change is based on the LLVM RTDyldMemoryManager.cpp. It should
later be changed to be alignment-safe.

Reported by:	dim
Reviewed by:	dim
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D8869
---
 .../libunwind/src/UnwindLevel1-gcc-ext.c      | 42 +++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/contrib/llvm/projects/libunwind/src/UnwindLevel1-gcc-ext.c b/contrib/llvm/projects/libunwind/src/UnwindLevel1-gcc-ext.c
index 61af9e8eade8..3d33dbb6a515 100644
--- a/contrib/llvm/projects/libunwind/src/UnwindLevel1-gcc-ext.c
+++ b/contrib/llvm/projects/libunwind/src/UnwindLevel1-gcc-ext.c
@@ -224,6 +224,47 @@ _LIBUNWIND_EXPORT uintptr_t _Unwind_GetIPInfo(struct _Unwind_Context *context,
 
 #if _LIBUNWIND_SUPPORT_DWARF_UNWIND
 
+#ifdef __FreeBSD__
+
+// Based on LLVM's lib/ExecutionEngine/RuntimeDyld/RTDyldMemoryManager.cpp
+// and XXX should be fixed to be alignment-safe.
+static void processFDE(const char *addr, bool isDeregister) {
+  uint64_t length;
+  while ((length = *((const uint32_t *)addr)) != 0) {
+    const char *p = addr + 4;
+    if (length == 0xffffffff) {
+      length = *((const uint64_t *)p);
+      p += 8;
+    }
+    uint32_t offset = *((const uint32_t *)p);
+    if (offset != 0) {
+      if (isDeregister)
+        _unw_remove_dynamic_fde((unw_word_t)(uintptr_t)addr);
+      else
+        _unw_add_dynamic_fde((unw_word_t)(uintptr_t)addr);
+    }
+    addr = p + length;
+  }
+}
+
+/// Called by programs with dynamic code generators that want to register
+/// dynamically generated FDEs, with a libgcc-compatible API.
+
+_LIBUNWIND_EXPORT void __register_frame(const void *addr) {
+  _LIBUNWIND_TRACE_API("__register_frame(%p)", addr);
+  processFDE(addr, false);
+}
+
+/// Called by programs with dynamic code generators that want to unregister
+/// dynamically generated FDEs, with a libgcc-compatible API.
+_LIBUNWIND_EXPORT void __deregister_frame(const void *addr) {
+  _LIBUNWIND_TRACE_API("__deregister_frame(%p)", addr);
+  processFDE(addr, true);
+}
+
+
+#else
+
 /// Called by programs with dynamic code generators that want
 /// to register a dynamically generated FDE.
 /// This function has existed on Mac OS X since 10.4, but
@@ -243,6 +284,7 @@ _LIBUNWIND_EXPORT void __deregister_frame(const void *fde) {
   _unw_remove_dynamic_fde((unw_word_t)(uintptr_t) fde);
 }
 
+#endif
 
 // The following register/deregister functions are gcc extensions.
 // They have existed on Mac OS X, but have never worked because Mac OS X