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Add initial experimental LTO support

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This will not succeed in compiling on all target and compiler
combinations but at least gets the ball rolling. The change is not
invasive.

Some notes:
- GCC has issues with LTO on ARM
- Clang uses LLD automatically on some arch
- Clang with LTO fails on x86 as it forwards the linking to GCC for some
  reason
- SMM building succeeds but the binary is empty

Change-Id: Ieb9204777fd349542744a8946e2207731c37969c
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/84003
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
This commit is contained in:
Arthur Heymans 2024-08-21 10:12:16 +02:00 • committed by Felix Held
commit b56f407614
2 changed files with 22 additions and 3 deletions
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18
Makefile.mk
View file

@ -373,7 +373,7 @@ endef
cbfs-files-processor-struct= \
$(eval $(2): $(1) $(obj)/build.h $(obj)/fmap_config.h $(KCONFIG_AUTOHEADER); \
printf " CC+STRIP $(1)\n"; \
$(CC_ramstage) -MMD $(CPPFLAGS_ramstage) $(CFLAGS_ramstage) --param asan-globals=0 $$(ramstage-c-ccopts) -include $(KCONFIG_AUTOHEADER) -MT $(2) -o $(2).tmp -c $(1) && \
$(CC_ramstage) -MMD $(CPPFLAGS_ramstage) $(CFLAGS_ramstage) -fno-lto --param asan-globals=0 $$(ramstage-c-ccopts) -include $(KCONFIG_AUTOHEADER) -MT $(2) -o $(2).tmp -c $(1) && \
$(OBJCOPY_ramstage) -O binary --only-section='.*data*' --only-section='.*bss*' \
--set-section-flags .*bss*=alloc,contents,load $(2).tmp $(2); \
rm -f $(2).tmp) \
@ -547,6 +547,14 @@ CFLAGS_common += -Wno-array-compare
endif
endif
ifeq ($(CONFIG_LTO),y)
CFLAGS_common += -flto
# Clang can not deal with GCC lto objects
ifeq ($(CONFIG_COMPILER_GCC),y)
ADAFLAGS_common += -flto
endif
endif
ADAFLAGS_common += -gnatp
ADAFLAGS_common += -Wuninitialized
ADAFLAGS_common += -Wall
@ -1316,11 +1324,15 @@ endif # CONFIG_CBFS_VERIFICATION
define link_stage
# $1 stage name
ifeq ($(CONFIG_LTO),y)
$$(objcbfs)/$(1).debug: $$$$($(1)-libs) $$$$($(1)-objs)
@printf " LINK $$(subst $$(obj)/,,$$(@))\n"
$$(CC_$(1)) $$(CPPFLAGS_$(1)) $$(CFLAGS_$(1)) $$(LDFLAGS_$(1):%=-Wl,%) -o $$@ -L$$(obj) $$(COMPILER_RT_FLAGS_$(1):%=-Wl,%) -Wl,--whole-archive -Wl,--start-group $$(filter-out %.ld,$$($(1)-objs)) $$($(1)-libs) -Wl,--no-whole-archive $$(COMPILER_RT_$(1)) -Wl,--end-group -T $(call src-to-obj,$(1),$(CONFIG_MEMLAYOUT_LD_FILE))
else
$$(objcbfs)/$(1).debug: $$$$($(1)-libs) $$$$($(1)-objs)
@printf " LINK $$(subst $$(obj)/,,$$(@))\n"
$$(LD_$(1)) $$(LDFLAGS_$(1)) -o $$@ -L$$(obj) $$(COMPILER_RT_FLAGS_$(1)) --whole-archive --start-group $$(filter-out %.ld,$$($(1)-objs)) $$($(1)-libs) --no-whole-archive $$(COMPILER_RT_$(1)) --end-group -T $(call src-to-obj,$(1),$(CONFIG_MEMLAYOUT_LD_FILE))
endif
endef
ifeq ($(CONFIG_SEPARATE_ROMSTAGE),y)

7
src/Kconfig
View file

@ -116,6 +116,13 @@ config CCACHE
For details see https://ccache.samba.org.
config LTO
bool "Use link time optimization (LTO) (experimental)"
default n
help
Compile with link time optimization. This can often decrease the
final binary size, but may increase compilation time.
config IWYU
bool "Test platform with include-what-you-use"
help