From b9f1b721c16970687690a0b4146d0c7346d355c2 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Wed, 18 May 2016 22:26:36 +0000
Subject: [PATCH] Work around a glibc bug: backtrace() spuriously fails if  -
 glibc is dynamically linked, and  - libgcc_s is unavailable (for instance,
 another library is being used to    provide the compiler runtime or libgcc is
 statically linked), and  - the target is x86_64.

If we run backtrace() and it fails to find any stack frames, try using
_Unwind_Backtrace instead if available.

llvm-svn: 269992
---
 cmake/config-ix.cmake        |  1 +
 lib/Support/Unix/Signals.inc | 55 +++++++++++++++++++++++++++++++++---
 2 files changed, 52 insertions(+), 4 deletions(-)

diff --git a/cmake/config-ix.cmake b/cmake/config-ix.cmake
index 7d5277517a9..b3f225f0740 100755
--- a/cmake/config-ix.cmake
+++ b/cmake/config-ix.cmake
@@ -144,6 +144,7 @@ endif()
 # function checks
 check_symbol_exists(arc4random "stdlib.h" HAVE_DECL_ARC4RANDOM)
 check_symbol_exists(backtrace "execinfo.h" HAVE_BACKTRACE)
+check_symbol_exists(_Unwind_Backtrace "unwind.h" HAVE_UNWIND_BACKTRACE)
 check_symbol_exists(getpagesize unistd.h HAVE_GETPAGESIZE)
 check_symbol_exists(getrusage sys/resource.h HAVE_GETRUSAGE)
 check_symbol_exists(setrlimit sys/resource.h HAVE_SETRLIMIT)
diff --git a/lib/Support/Unix/Signals.inc b/lib/Support/Unix/Signals.inc
index 061cdb3da21..27f3414ce57 100644
--- a/lib/Support/Unix/Signals.inc
+++ b/lib/Support/Unix/Signals.inc
@@ -45,6 +45,9 @@
 #if HAVE_LINK_H
 #include <link.h>
 #endif
+#if HAVE_UNWIND_BACKTRACE
+#include <unwind.h>
+#endif
 
 using namespace llvm;
 
@@ -309,17 +312,61 @@ static bool findModulesAndOffsets(void **StackTrace, int Depth,
 }
 #endif // defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES) && ...
 
+#if defined(ENABLE_BACKTRACES) && defined(HAVE_UNWIND_BACKTRACE)
+static int unwindBacktrace(void **StackTrace, int MaxEntries) {
+  if (MaxEntries < 0)
+    return 0;
+
+  // Skip the first frame ('unwindBacktrace' itself).
+  int Entries = -1;
+
+  auto HandleFrame = [&](_Unwind_Context *Context) -> _Unwind_Reason_Code {
+    // Apparently we need to detect reaching the end of the stack ourselves.
+    void *IP = (void *)_Unwind_GetIP(Context);
+    if (!IP)
+      return _URC_END_OF_STACK;
+
+    assert(Entries < MaxEntries && "recursively called after END_OF_STACK?");
+    if (Entries >= 0)
+      StackTrace[Entries] = IP;
+
+    if (++Entries == MaxEntries)
+      return _URC_END_OF_STACK;
+    return _URC_NO_REASON;
+  };
+
+  _Unwind_Backtrace(
+      [](_Unwind_Context *Context, void *Handler) {
+        return (*static_cast<decltype(HandleFrame) *>(Handler))(Context);
+      },
+      static_cast<void *>(&HandleFrame));
+  return std::max(Entries, 0);
+}
+#endif
+
 // PrintStackTrace - In the case of a program crash or fault, print out a stack
 // trace so that the user has an indication of why and where we died.
 //
 // On glibc systems we have the 'backtrace' function, which works nicely, but
 // doesn't demangle symbols.
 void llvm::sys::PrintStackTrace(raw_ostream &OS) {
-#if defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES)
-  static void* StackTrace[256];
+#if defined(ENABLE_BACKTRACES)
+  static void *StackTrace[256];
+  int depth = 0;
+#if defined(HAVE_BACKTRACE)
   // Use backtrace() to output a backtrace on Linux systems with glibc.
-  int depth = backtrace(StackTrace,
+  if (!depth)
+    depth = backtrace(StackTrace, static_cast<int>(array_lengthof(StackTrace)));
+#endif
+#if defined(HAVE_UNWIND_BACKTRACE)
+  // Try _Unwind_Backtrace() if backtrace() failed.
+  if (!depth)
+    depth = unwindBacktrace(StackTrace,
                         static_cast<int>(array_lengthof(StackTrace)));
+#endif
+  if (!depth)
+    return;
+
   if (printSymbolizedStackTrace(StackTrace, depth, OS))
     return;
 #if HAVE_DLFCN_H && __GNUG__
@@ -369,7 +416,7 @@ void llvm::sys::PrintStackTrace(raw_ostream &OS) {
     }
     OS << '\n';
   }
-#else
+#elif defined(HAVE_BACKTRACE)
   backtrace_symbols_fd(StackTrace, depth, STDERR_FILENO);
 #endif
 #endif