[scudo] Use gc-sections by default

Summary:
If not using `-Wl,--gc-sections`, a whole lot of unused `sanitizer_common` code
and related static variables are pulled into the shared library.
Keep the binary size smaller, and its memory footprint smaller as well, by
using the compiler flags `-ffunction-section` & `-fdata-sections` by default,
as well as the linker flags `-Wl,--gc-sections`.

Current experiments show a large discrepency between binary sizes generated
by gcc (big) and clang (small). I am not sure yet how I can make a test that
would encompass both, so it's an outstanding work item.

Reviewers: alekseyshl, flowerhack

Reviewed By: alekseyshl

Subscribers: mgorny, delcypher, llvm-commits, #sanitizers

Differential Revision: https://reviews.llvm.org/D44121

llvm-svn: 326833

diff --git a/compiler-rt/lib/scudo/CMakeLists.txt b/compiler-rt/lib/scudo/CMakeLists.txt
index 29e6795..0aba0ca 100644 (file)
--- a/compiler-rt/lib/scudo/CMakeLists.txt
+++ b/compiler-rt/lib/scudo/CMakeLists.txt
@@ -9,6 +9,10 @@ append_rtti_flag(OFF SCUDO_CFLAGS)
 
 set(SCUDO_DYNAMIC_LINK_FLAGS ${SANITIZER_COMMON_LINK_FLAGS})
 
+# Use gc-sections by default to avoid unused code being pulled in.
+list(APPEND SCUDO_CFLAGS -ffunction-sections -fdata-sections)
+list(APPEND SCUDO_DYNAMIC_LINK_FLAGS -Wl,--gc-sections)
+
 set(SCUDO_SOURCES
   scudo_allocator.cpp
   scudo_crc32.cpp