Add the ability to link against a debug build of libunwind for debugging...

Add the ability to link against a debug build of libunwind for debugging unwinding issues, and some basic instructions on how to do so

docs/INSTALLING.md

@@ -98,6 +98,23 @@ VALGRIND := VALGRIND_LIB=$(HOME)/pyston_deps/valgrind-3.9.0-install/lib/valgrind
 
 # Optional dependencies
 
+### Debug build of libunwind
+
+Assuming you've already built the normal version above:
+
+```
+cd ~/pyston_deps
+cp -rv libunwind-1.1 libunwind-1.1-debug
+mkdir ../libunwind-1.1-debug-install
+cd libunwind-1.1-debug
+./configure --prefix=$HOME/pyston_deps/libunwind-1.1-debug-install --enable-shared=0 --enable-debug --enable-debug-frame
+make -j4
+make install
+echo "USE_DEBUG_LIBUNWIND := 1" >> ~/pyston/src/Makefile.local
+```
+
+This will link pyston_dbg and pyston_debug against the debug version of libunwind (the release pyston build will still link against the release libunwind); to enable debug output, set the UNW_DEBUG_LEVEL environment variable, ex to 13.
+
 ### distcc
 ```
 sudo apt-get install distcc distcc-pump

src/Makefile

@@ -16,6 +16,8 @@ GDB := gdb
 GCC_DIR := $(DEPS_DIR)/gcc-4.8.2-install
 GTEST_DIR := $(DEPS_DIR)/gtest-1.7.0
 
+USE_DEBUG_LIBUNWIND := 0
+
 PYTHON_MAJOR_VERSION := 2
 PYTHON_MINOR_VERSION := 7
 PYTHON_MICRO_VERSION := 3
@@ -141,8 +143,6 @@ COMMON_LDFLAGS := -B../tools/build_system -L/usr/local/lib -lpthread -ldl -lcurs
 # TODO should probably do the linking before MCJIT
 COMMON_LDFLAGS += -Wl,-E
 
-COMMON_LDFLAGS += -L$(DEPS_DIR)/libunwind-1.1-install/lib
-
 # The system libstdc++ will likely be too old for Pyston, but we made a brand new one
 # as part of our GCC installation.  There are a couple ways to use that one instead:
 # 1) Install the built libstdc++ (~/pyston_deps/gcc-4.8.2-install/lib64/libstdc++.so.6.0.18) and update the global shared library (/usr/local/x86_64-linux-gnu/libstdc++.so.6) to point to it
@@ -164,6 +164,17 @@ LDFLAGS_RELEASE := $(LLVM_RELEASE_LDFLAGS) $(COMMON_LDFLAGS)
 # Can't add this, because there are functions in the compiler that look unused but are hooked back from the runtime:
 # LDFLAGS_RELEASE += -Wl,--gc-sections
 
+ifneq ($(USE_DEBUG_LIBUNWIND),0)
+	LDFLAGS += -L$(DEPS_DIR)/libunwind-1.1-debug-install/lib
+	LDFLAGS_DEBUG += -L$(DEPS_DIR)/libunwind-1.1-debug-install/lib
+else
+	LDFLAGS += -L$(DEPS_DIR)/libunwind-1.1-install/lib
+	LDFLAGS_DEBUG += -L$(DEPS_DIR)/libunwind-1.1-install/lib
+endif
+LDFLAGS_RELEASE += -L$(DEPS_DIR)/libunwind-1.1-install/lib
+LDFLAGS_PROFILE += -L$(DEPS_DIR)/libunwind-1.1-install/lib
+
+
 BUILD_SYSTEM_DEPS := Makefile Makefile.local $(wildcard build_system/*)
 CLANG_DEPS := $(CLANG_EXE) $(abspath $(dir $(CLANG_EXE))/../../built_release)