libcxxabi contains the runtime support for C++. But, as some folks have

realized, it is not complete.  It relies on some _Unwind_* functions to be
supplied by the OS. That means it cannot be ported to platforms that don’t 
already have an unwinder.  

Years ago Apple wrote its own unwinder for MacOSX and iOS.  To make libcxxabi 
complete, Apple has decided the source code for its unwinder can be contributed
to the open source LLVM libcxxabi project, with a dual licensed under LLVM 
and MIT license.

So, I’ve spent some time cleaning up the sources to make them conform with 
LLVM style and to conditionalize the sources in a way that should make it 
easier to port to other platforms.  The sources are in a separate "Unwind" 
directory under "src" in libcxxabi.  

Background:
Most architectures now use "zero cost" exceptions for C++.  The zero cost means
there are no extra instructions executed if no exceptions are thrown.  But if 
an exception is thrown, the runtime must consult side tables and figure out how
to restore registers and "unwind" from the current stack frame to the catch 
clause.  That ability to modify the stack frames and cause the thread to resume 
in a catch clause with all registers restored properly is the main purpose 
of the unwinder.

This unwinder has two levels of API.  The high level APIs are the _Unwind_* 
functions which the cxa_* exception functions in libcxxabi require.  The low 
level APIs are the unw_* functions which are an interface defined by the the 
old HP libunwind project (which shares no code with this unwinder).


git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@192136 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 108 insertions, 0 deletions

diff --git a/src/Unwind/config.h b/src/Unwind/config.h
new file mode 100644
index 0000000..2b92464
--- /dev/null
+++ b/src/Unwind/config.h
@@ -0,0 +1,108 @@
+//===----------------------------- config.h -------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//
+//  Defines macros used within libuwind project.
+//
+//===----------------------------------------------------------------------===//
+
+
+#ifndef LIBUNWIND_CONFIG_H
+#define LIBUNWIND_CONFIG_H
+
+#include <assert.h>
+
+// Define static_assert() unless already defined by compiler.
+#ifndef __has_feature
+  #define __has_feature(__x) 0
+#endif
+#if !(__has_feature(cxx_static_assert))
+  #define static_assert(__b, __m) \
+      extern int compile_time_assert_failed[ ( __b ) ? 1 : -1 ]  \
+                                                  __attribute__( ( unused ) );
+#endif
+
+// Platform specific configuration defines.
+#if __APPLE__
+  #include <Availability.h>
+  #ifdef __cplusplus
+    extern "C" {
+  #endif
+    void __assert_rtn(const char *, const char *, int, const char *)
+                                                      __attribute__((noreturn));
+  #ifdef __cplusplus
+    }
+  #endif
+
+  #define _LIBUNWIND_BUILD_ZERO_COST_APIS (__i386__ || __x86_64__ || __arm64__)
+  #define _LIBUNWIND_BUILD_SJLJ_APIS      (__arm__)
+  #define _LIBUNWIND_SUPPORT_FRAME_APIS   (__i386__ || __x86_64__)
+  #define _LIBUNWIND_EXPORT               __attribute__((visibility("default")))
+  #define _LIBUNWIND_HIDDEN               __attribute__((visibility("hidden")))
+  #define _LIBUNWIND_LOG(msg, ...) fprintf(stderr, "libuwind: " msg, __VA_ARGS__)
+  #define _LIBUNWIND_ABORT(msg) __assert_rtn(__func__, __FILE__, __LINE__, msg)
+
+  #if FOR_DYLD
+    #define _LIBUNWIND_SUPPORT_COMPACT_UNWIND 1
+    #define _LIBUNWIND_SUPPORT_DWARF_UNWIND   0
+    #define _LIBUNWIND_SUPPORT_DWARF_INDEX    0
+  #else
+    #define _LIBUNWIND_SUPPORT_COMPACT_UNWIND 1
+    #define _LIBUNWIND_SUPPORT_DWARF_UNWIND   1
+    #define _LIBUNWIND_SUPPORT_DWARF_INDEX    0
+  #endif
+
+#else
+  // #define _LIBUNWIND_BUILD_ZERO_COST_APIS
+  // #define _LIBUNWIND_BUILD_SJLJ_APIS
+  // #define _LIBUNWIND_SUPPORT_FRAME_APIS
+  // #define _LIBUNWIND_EXPORT
+  // #define _LIBUNWIND_HIDDEN
+  // #define _LIBUNWIND_LOG()
+  // #define _LIBUNWIND_ABORT()
+  // #define _LIBUNWIND_SUPPORT_COMPACT_UNWIND
+  // #define _LIBUNWIND_SUPPORT_DWARF_UNWIND
+  // #define _LIBUNWIND_SUPPORT_DWARF_INDEX
+#endif
+
+
+// Macros that define away in non-Debug builds
+#ifdef NDEBUG
+  #define _LIBUNWIND_DEBUG_LOG(msg, ...)
+  #define _LIBUNWIND_TRACE_API(msg, ...)
+  #define _LIBUNWIND_TRACING_UNWINDING 0
+  #define _LIBUNWIND_TRACE_UNWINDING(msg, ...)
+  #define _LIBUNWIND_LOG_NON_ZERO(x) x
+#else
+  #ifdef __cplusplus
+    extern "C" {
+  #endif
+    extern  bool logAPIs();
+    extern  bool logUnwinding();
+  #ifdef __cplusplus
+    }
+  #endif
+  #define _LIBUNWIND_DEBUG_LOG(msg, ...)  _LIBUNWIND_LOG(msg, __VA_ARGS__)
+  #define _LIBUNWIND_LOG_NON_ZERO(x) \
+            do { \
+              int _err = x; \
+              if ( _err != 0 ) \
+                _LIBUNWIND_LOG("" #x "=%d in %s", _err, __FUNCTION__); \
+             } while (0)
+  #define _LIBUNWIND_TRACE_API(msg, ...) \
+            do { \
+              if ( logAPIs() ) _LIBUNWIND_LOG(msg, __VA_ARGS__); \
+            } while(0)
+  #define _LIBUNWIND_TRACE_UNWINDING(msg, ...) \
+            do { \
+              if ( logUnwinding() ) _LIBUNWIND_LOG(msg, __VA_ARGS__); \
+            } while(0)
+  #define _LIBUNWIND_TRACING_UNWINDING logUnwinding()
+#endif
+
+
+#endif // LIBUNWIND_CONFIG_H