[libunwind] Add support for a single-threaded libunwind build

[rmaprath]

Summary

The EHABI unwinder is thread-agnostic, SJLJ unwinder and the DWARF unwinder have a couple of pthread dependencies.

This patch makes it possible to build the whole of libunwind for a single-threaded environment.

CMakeLists.txt

 option(LIBUNWIND_BUILD_32_BITS "Build 32 bit libunwind" ${LLVM_BUILD_32_BITS})
 option(LIBUNWIND_ENABLE_ASSERTIONS "Enable assertions independent of build mode." ON)
 option(LIBUNWIND_ENABLE_PEDANTIC "Compile with pedantic enabled." ON)
 option(LIBUNWIND_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
 option(LIBUNWIND_ENABLE_SHARED "Build libunwind as a shared library." ON)
 option(LIBUNWIND_ENABLE_STATIC "Build libunwind as a static library." ON)
 option(LIBUNWIND_ENABLE_CROSS_UNWINDING "Enable cross-platform unwinding support." OFF)
 option(LIBUNWIND_ENABLE_ARM_WMMX "Enable unwinding support for ARM WMMX registers." OFF)
+option(LIBUNWIND_ENABLE_THREADS "Build libunwind with threading support." ON)
 
 set(LIBUNWIND_TARGET_TRIPLE "" CACHE STRING "Target triple for cross compiling.")
 set(LIBUNWIND_GCC_TOOLCHAIN "" CACHE PATH "GCC toolchain for cross compiling.")
 set(LIBUNWIND_SYSROOT "" CACHE PATH "Sysroot for cross compiling.")
 
 if (NOT LIBUNWIND_ENABLE_SHARED AND NOT LIBUNWIND_ENABLE_STATIC)
   message(FATAL_ERROR "libunwind must be built as either a shared or static library.")
 endif()

   endif()
 endif()
 
 # Cross-unwinding
 if (NOT LIBUNWIND_ENABLE_CROSS_UNWINDING)
   list(APPEND LIBUNWIND_COMPILE_FLAGS -D_LIBUNWIND_IS_NATIVE_ONLY)
 endif()
 
+# Threading-support
+if (NOT LIBUNWIND_ENABLE_THREADS)
+  list(APPEND LIBUNWIND_COMPILE_FLAGS -D_LIBUNWIND_HAS_NO_THREADS)
+endif()
+
 # ARM WMMX register support
 if (LIBUNWIND_ENABLE_ARM_WMMX)
   # __ARM_WMMX is a compiler pre-define (as per the ACLE 2.0). Clang does not
   # define this macro for any supported target at present. Therefore, here we
   # provide the option to explicitly enable support for WMMX registers in the
   # unwinder.
   list(APPEND LIBUNWIND_COMPILE_FLAGS -D__ARM_WMMX)
 endif()

src/CMakeLists.txt

set(LIBUNWIND_SOURCES
     ${LIBUNWIND_CXX_SOURCES}
     ${LIBUNWIND_C_SOURCES}
     ${LIBUNWIND_ASM_SOURCES})
 
 # Generate library list.
 set(libraries ${LIBUNWINDCXX_ABI_LIBRARIES})
 append_if(libraries LIBUNWIND_HAS_C_LIB c)
 append_if(libraries LIBUNWIND_HAS_DL_LIB dl)
+if (LIBUNWIND_ENABLE_THREADS)
   append_if(libraries LIBUNWIND_HAS_PTHREAD_LIB pthread)
+endif()
 
 # Setup flags.
 append_if(LIBUNWIND_COMPILE_FLAGS LIBUNWIND_HAS_FPIC_FLAG -fPIC)
 append_if(LIBUNWIND_CXX_FLAGS LIBUNWIND_HAS_NO_RTTI_FLAG -fno-rtti)
 
 append_if(LIBUNWIND_LINK_FLAGS LIBUNWIND_HAS_NODEFAULTLIBS_FLAG -nodefaultlibs)
 
 if (LIBUNWIND_HAS_NO_EXCEPTIONS_FLAG AND LIBUNWIND_HAS_FUNWIND_TABLES)

src/UnwindCursor.hpp

 
 #ifndef __UNWINDCURSOR_HPP__
 #define __UNWINDCURSOR_HPP__
 
 #include <algorithm>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#ifndef _LIBUNWIND_HAS_NO_THREADS
   #include <pthread.h>
+#endif
 #include <unwind.h>
 
 #ifdef __APPLE__
   #include <mach-o/dyld.h>
 #endif
 
 #include "config.h"
 
struct entry {
     pint_t mh;
     pint_t ip_start;
     pint_t ip_end;
     pint_t fde;
   };
 
   // These fields are all static to avoid needing an initializer.
   // There is only one instance of this class per process.
+#ifndef _LIBUNWIND_HAS_NO_THREADS
   static pthread_rwlock_t _lock;
+#endif
 #ifdef __APPLE__
   static void dyldUnloadHook(const struct mach_header *mh, intptr_t slide);
   static bool _registeredForDyldUnloads;
 #endif
   // Can't use std::vector<> here because this code is below libc++.
   static entry *_buffer;
   static entry *_bufferUsed;
   static entry *_bufferEnd;

 
 template <typename A>
 typename DwarfFDECache<A>::entry *
 DwarfFDECache<A>::_bufferEnd = &_initialBuffer[64];
 
 template <typename A>
 typename DwarfFDECache<A>::entry DwarfFDECache<A>::_initialBuffer[64];
 
+#ifndef _LIBUNWIND_HAS_NO_THREADS
 template <typename A>
 pthread_rwlock_t DwarfFDECache<A>::_lock = PTHREAD_RWLOCK_INITIALIZER;
+#endif
 
 #ifdef __APPLE__
 template <typename A>
 bool DwarfFDECache<A>::_registeredForDyldUnloads = false;
 #endif
 
 template <typename A>
 typename A::pint_t DwarfFDECache<A>::findFDE(pint_t mh, pint_t pc) {

src/Unwind_AppleExtras.cpp

   return false;
 }
 
 }
 
 
 #if !defined(FOR_DYLD) && _LIBUNWIND_BUILD_SJLJ_APIS
 
-#include <System/pthread_machdep.h>
+#ifndef _LIBUNWIND_HAS_NO_THREADS
+  #include <System/pthread_machdep.h>
+#else
+  _Unwind_FunctionContext *fc_ = nullptr;
+#endif
 
 // Accessors to get get/set linked list of frames for sjlj based execeptions.
 _LIBUNWIND_HIDDEN
 struct _Unwind_FunctionContext *__Unwind_SjLj_GetTopOfFunctionStack() {
+#ifndef _LIBUNWIND_HAS_NO_THREADS
   return (struct _Unwind_FunctionContext *)
     _pthread_getspecific_direct(__PTK_LIBC_DYLD_Unwind_SjLj_Key);
+#else
+  return fc_;
+#endif
 }
 
 _LIBUNWIND_HIDDEN
 void __Unwind_SjLj_SetTopOfFunctionStack(struct _Unwind_FunctionContext *fc) {
+#ifndef _LIBUNWIND_HAS_NO_THREADS
   _pthread_setspecific_direct(__PTK_LIBC_DYLD_Unwind_SjLj_Key, fc);
+#else
+  fc_ = fc;
+#endif
 }
 #endif
-
-
-
-

src/config.h

#define _LIBUNWIND_ABORT(msg)                                                  \
   do {                                                                         \
     fprintf(stderr, "libunwind: %s %s:%d - %s\n", __func__, __FILE__,          \
             __LINE__, msg);                                                    \
     fflush(stderr);                                                            \
     abort();                                                                   \
   } while (0)
 #define _LIBUNWIND_LOG(msg, ...) fprintf(stderr, "libunwind: " msg "\n", __VA_ARGS__)
 
+#if defined(_LIBUNWIND_HAS_NO_THREADS)
+  // only used with pthread calls, not needed for the single-threaded builds
+  #define _LIBUNWIND_LOG_NON_ZERO(x)
+#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, ...)
+  #ifndef _LIBUNWIND_LOG_NON_ZERO
     #define _LIBUNWIND_LOG_NON_ZERO(x) x
+  #endif
 #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__)
+  #ifndef _LIBUNWIND_LOG_NON_ZERO
     #define _LIBUNWIND_LOG_NON_ZERO(x) \
               do { \
                 int _err = x; \
                 if ( _err != 0 ) \
                   _LIBUNWIND_LOG("" #x "=%d in %s", _err, __FUNCTION__); \
                } while (0)
+  #endif
   #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)