From 04540f1549a6fea5227ac9538edb8b2643c4d719 Mon Sep 17 00:00:00 2001 From: Jacob Garber Date: Wed, 2 Oct 2019 18:55:07 -0600 Subject: [PATCH] libpayload: Add support for link time optimization Link time optimization is a technique for whole-program optimization. Instead of doing code generation during compilation, the compiler saves its intermediate representation to the object files. During the final linking step, it will then merge all the object files together and perform optimizations on the entire program. This can often reduce the final binary size, but also may increase the total compilation time. This patch introduces a Kconfig option for enabling link time optimization in libpayload. Since libpayload does no linking of its own, its LTO archive files will contain only IR and no generated code. Downstream projects will need to use LTO-aware tools when manipulating the archives (eg. gcc-ar and gcc-nm), but otherwise do not need to use LTO themselves -- the compiler will recognize which files are LTO and which are not, so enabling this option should mostly be "drop in". For example, when building coreinfo.elf using tinycurses libpayload: binary size compilation time default 114 KiB 11.49s LTO 95 KiB 10.36s In this case the total compilation time was actually shorter -- despite the final linking step taking longer, this was offset by the shorter compilation times for each individual file (since there is no code gen until the very end). Change-Id: I048f2ff6298ed0d891098942e1e8b29d35487b91 Signed-off-by: Jacob Garber Reviewed-on: https://review.coreboot.org/c/coreboot/+/38291 Reviewed-by: Nico Huber Reviewed-by: Martin Roth Tested-by: build bot (Jenkins) --- payloads/libpayload/Kconfig | 8 ++++++++ payloads/libpayload/Makefile.inc | 4 ++++ 2 files changed, 12 insertions(+) diff --git a/payloads/libpayload/Kconfig b/payloads/libpayload/Kconfig index b5dc9a3c8b..f5b81a9f00 100644 --- a/payloads/libpayload/Kconfig +++ b/payloads/libpayload/Kconfig @@ -79,6 +79,14 @@ config COMPILER_LLVM_CLANG endchoice +config LTO + bool "Use link time optimization (LTO)" + default n + depends on COMPILER_GCC + help + Compile with link time optimization. This can often decrease the + final binary size, but may increase compilation time. + config REMOTEGDB bool "Remote GDB stub" default n diff --git a/payloads/libpayload/Makefile.inc b/payloads/libpayload/Makefile.inc index 2acf2266da..1b2a883b16 100644 --- a/payloads/libpayload/Makefile.inc +++ b/payloads/libpayload/Makefile.inc @@ -64,6 +64,10 @@ CFLAGS += -Wall -Wundef -Wstrict-prototypes -Wmissing-prototypes -Wvla CFLAGS += -Wwrite-strings -Wredundant-decls -Wno-trigraphs -Wimplicit-fallthrough CFLAGS += -Wstrict-aliasing -Wshadow -Werror +ifeq ($(CONFIG_LP_LTO),y) +CFLAGS += -flto +endif + $(obj)/libpayload-config.h: $(KCONFIG_AUTOHEADER) cmp $@ $< 2>/dev/null || cp $< $@