[llvm] r359819 - build: add option to disable unwind tables

[Saleem Abdulrasool via llvm-commits]

Author: compnerd
Date: Thu May  2 12:37:26 2019
New Revision: 359819

URL: http://llvm.org/viewvc/llvm-project?rev=359819&view=rev
Log:
build: add option to disable unwind tables

The unwind tables (`.eh_frame`, `.arm.extab`) add a significant chunk of data to
the final binaries.  These should not be needed normally, particularly when
exceptions are disabled.  This enables shrinking `lldb-server` by ~18% (3 MiB)
when built with gold.

Modified:
    llvm/trunk/CMakeLists.txt
    llvm/trunk/cmake/modules/AddLLVM.cmake
    llvm/trunk/docs/CMake.rst

Modified: llvm/trunk/CMakeLists.txt
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/CMakeLists.txt?rev=359819&r1=359818&r2=359819&view=diff
==============================================================================
--- llvm/trunk/CMakeLists.txt (original)
+++ llvm/trunk/CMakeLists.txt Thu May  2 12:37:26 2019
@@ -351,6 +351,8 @@ if(LLVM_ENABLE_BACKTRACES)
   set(ENABLE_BACKTRACES 1)
 endif()
 
+option(LLVM_ENABLE_UNWIND_TABLES "Emit unwind tables for the libraries" ON)
+
 option(LLVM_ENABLE_CRASH_OVERRIDES "Enable crash overrides." ON)
 if(LLVM_ENABLE_CRASH_OVERRIDES)
   set(ENABLE_CRASH_OVERRIDES 1)

Modified: llvm/trunk/cmake/modules/AddLLVM.cmake
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/cmake/modules/AddLLVM.cmake?rev=359819&r1=359818&r2=359819&view=diff
==============================================================================
--- llvm/trunk/cmake/modules/AddLLVM.cmake (original)
+++ llvm/trunk/cmake/modules/AddLLVM.cmake Thu May  2 12:37:26 2019
@@ -21,6 +21,10 @@ function(llvm_update_compile_flags name)
   else()
     if(LLVM_COMPILER_IS_GCC_COMPATIBLE)
       list(APPEND LLVM_COMPILE_FLAGS "-fno-exceptions")
+      if(NOT LLVM_ENABLE_UNWIND_TABLES)
+        list(APPEND LLVM_COMPILE_FLAGS "-fno-unwind-tables")
+        list(APPEND LLVM_COMPILE_FLAGS "-fno-asynchronous-unwind-tables")
+      endif()
     elseif(MSVC)
       list(APPEND LLVM_COMPILE_DEFINITIONS _HAS_EXCEPTIONS=0)
       list(APPEND LLVM_COMPILE_FLAGS "/EHs-c-")

Modified: llvm/trunk/docs/CMake.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/docs/CMake.rst?rev=359819&r1=359818&r2=359819&view=diff
==============================================================================
--- llvm/trunk/docs/CMake.rst (original)
+++ llvm/trunk/docs/CMake.rst Thu May  2 12:37:26 2019
@@ -266,6 +266,10 @@ LLVM-specific variables
 **LLVM_ENABLE_THREADS**:BOOL
   Build with threads support, if available. Defaults to ON.
 
+**LLVM_ENABLE_UNWIND_TABLES**:BOOL
+  Enable unwind tables in the binary.  Disabling unwind tables can reduce the
+  size of the libraries.  Defaults to ON.
+
 **LLVM_CXX_STD**:STRING
   Build with the specified C++ standard. Defaults to "c++11".