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authorSami Tolvanen <samitolvanen@google.com>2020-12-11 10:46:19 -0800
committerKees Cook <keescook@chromium.org>2021-01-14 08:21:08 -0800
commitdc5723b02e523b2c4a68667f7e28c65018f7202f (patch)
treee31da4c11f359712314d351d6b4281739785adfe /Makefile
parent3b15cdc15956673ba1551d79bceae471436ac6a9 (diff)
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kbuild: add support for Clang LTO
This change adds build system support for Clang's Link Time Optimization (LTO). With -flto, instead of ELF object files, Clang produces LLVM bitcode, which is compiled into native code at link time, allowing the final binary to be optimized globally. For more details, see: https://llvm.org/docs/LinkTimeOptimization.html The Kconfig option CONFIG_LTO_CLANG is implemented as a choice, which defaults to LTO being disabled. To use LTO, the architecture must select ARCH_SUPPORTS_LTO_CLANG and support: - compiling with Clang, - compiling all assembly code with Clang's integrated assembler, - and linking with LLD. While using CONFIG_LTO_CLANG_FULL results in the best runtime performance, the compilation is not scalable in time or memory. CONFIG_LTO_CLANG_THIN enables ThinLTO, which allows parallel optimization and faster incremental builds. ThinLTO is used by default if the architecture also selects ARCH_SUPPORTS_LTO_CLANG_THIN: https://clang.llvm.org/docs/ThinLTO.html To enable LTO, LLVM tools must be used to handle bitcode files, by passing LLVM=1 and LLVM_IAS=1 options to make: $ make LLVM=1 LLVM_IAS=1 defconfig $ scripts/config -e LTO_CLANG_THIN $ make LLVM=1 LLVM_IAS=1 To prepare for LTO support with other compilers, common parts are gated behind the CONFIG_LTO option, and LTO can be disabled for specific files by filtering out CC_FLAGS_LTO. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20201211184633.3213045-3-samitolvanen@google.com
Diffstat (limited to 'Makefile')
-rw-r--r--Makefile19
1 files changed, 17 insertions, 2 deletions
diff --git a/Makefile b/Makefile
index b434c342080b..2b9bcecd6ea1 100644
--- a/Makefile
+++ b/Makefile
@@ -893,6 +893,21 @@ KBUILD_CFLAGS += $(CC_FLAGS_SCS)
export CC_FLAGS_SCS
endif
+ifdef CONFIG_LTO_CLANG
+ifdef CONFIG_LTO_CLANG_THIN
+CC_FLAGS_LTO += -flto=thin -fsplit-lto-unit
+KBUILD_LDFLAGS += --thinlto-cache-dir=$(extmod-prefix).thinlto-cache
+else
+CC_FLAGS_LTO += -flto
+endif
+CC_FLAGS_LTO += -fvisibility=hidden
+endif
+
+ifdef CONFIG_LTO
+KBUILD_CFLAGS += $(CC_FLAGS_LTO)
+export CC_FLAGS_LTO
+endif
+
ifdef CONFIG_DEBUG_FORCE_FUNCTION_ALIGN_32B
KBUILD_CFLAGS += -falign-functions=32
endif
@@ -1479,7 +1494,7 @@ MRPROPER_FILES += include/config include/generated \
*.spec
# Directories & files removed with 'make distclean'
-DISTCLEAN_FILES += tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS
+DISTCLEAN_FILES += tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS .thinlto-cache
# clean - Delete most, but leave enough to build external modules
#
@@ -1725,7 +1740,7 @@ PHONY += compile_commands.json
clean-dirs := $(KBUILD_EXTMOD)
clean: rm-files := $(KBUILD_EXTMOD)/Module.symvers $(KBUILD_EXTMOD)/modules.nsdeps \
- $(KBUILD_EXTMOD)/compile_commands.json
+ $(KBUILD_EXTMOD)/compile_commands.json $(KBUILD_EXTMOD)/.thinlto-cache
PHONY += help
help: