From: Waldemar Kozaczuk <[email protected]> Committer: Waldemar Kozaczuk <[email protected]> Branch: master
makefile: enable garbage collection of code and data when hiding symbols This patch changes the main makefile to enable garbage collection of code and data when linking kernel with most symbols hidden. In essence it makes all object files compile with '-ffunction-sections -fdata-sections' flags only when conf_hide_symbols is ON. This allows linker to eliminate code and data (with --gc-sections) that is not really used between various compilation units. As the result it allows us to produce even smaller kernel ELF at around 4.3M, down from 5.1M when we would hide symbols only. In order to see what exact code and data gets eliminated, one can pass --print-gc-sections flags to the linker like so: ./scripts/build image=native-example fs=rofs conf_hide_symbols=1 conf_linker_extra_options=--print-gc-sections In addition this patch also changes the makefile to make linker use version script generated by ./scripts/generate_version_script.sh which is obnly enabled when conf_hide_symbols is ON. Using version script (--version-script) plays some role in futher reducing number of symbols down to what exactly we want to export in exported/<arch>/*symbols. Signed-off-by: Waldemar Kozaczuk <[email protected]> --- diff --git a/Makefile b/Makefile --- a/Makefile +++ b/Makefile @@ -284,7 +284,7 @@ $(out)/libc/%.o: cc-hide-flags = $(out)/libc/%.o: cxx-hide-flags = $(out)/musl/%.o: cc-hide-flags = -kernel-defines = -D_KERNEL $(source-dialects) $(cc-hide-flags) +kernel-defines = -D_KERNEL $(source-dialects) $(cc-hide-flags) $(gc-flags) # This play the same role as "_KERNEL", but _KERNEL unfortunately is too # overloaded. A lot of files will expect it to be set no matter what, specially @@ -323,6 +323,10 @@ cxx-hide-flags-0 = cxx-hide-flags-1 = -fvisibility-inlines-hidden cxx-hide-flags = $(cxx-hide-flags-$(conf_hide_symbols)) +gc-flags-0 = +gc-flags-1 = -ffunction-sections -fdata-sections +gc-flags = $(gc-flags-$(conf_hide_symbols)) + gcc-opt-Og := $(call compiler-flag, -Og, -Og, compiler/empty.cc) CXXFLAGS = -std=gnu++11 $(COMMON) $(cxx-hide-flags) @@ -1944,7 +1948,7 @@ $(out)/dummy-shlib.so: $(out)/dummy-shlib.o $(call quiet, $(CXX) -nodefaultlibs -shared $(gcc-sysroot) -o $@ $^, LINK $@) stage1_targets = $(out)/arch/$(arch)/boot.o $(out)/loader.o $(out)/runtime.o $(drivers:%=$(out)/%) $(objects:%=$(out)/%) $(out)/dummy-shlib.so -stage1: $(stage1_targets) links +stage1: $(stage1_targets) links $(out)/version_script .PHONY: stage1 loader_options_dep = $(out)/arch/$(arch)/loader_options.ld @@ -1955,17 +1959,21 @@ $(loader_options_dep): stage1 fi ifeq ($(conf_hide_symbols),1) -linker_archives_options = --no-whole-archive $(libstdc++.a) $(libgcc.a) $(libgcc_eh.a) $(boost-libs) --exclude-libs libstdc++.a +linker_archives_options = --no-whole-archive $(libstdc++.a) $(libgcc.a) $(libgcc_eh.a) $(boost-libs) \ + --exclude-libs libstdc++.a --gc-sections --version-script=$(out)/version_script else linker_archives_options = --whole-archive $(libstdc++.a) $(libgcc_eh.a) $(boost-libs) --no-whole-archive $(libgcc.a) endif +$(out)/version_script: exported_symbols/$(arch)/*.symbols + $(call quiet, scripts/generate_version_script.sh $(out)/version_script, GEN version_script) + $(out)/loader.elf: $(stage1_targets) arch/$(arch)/loader.ld $(out)/bootfs.o $(loader_options_dep) $(call quiet, $(LD) -o $@ --defsym=OSV_KERNEL_BASE=$(kernel_base) \ --defsym=OSV_KERNEL_VM_BASE=$(kernel_vm_base) --defsym=OSV_KERNEL_VM_SHIFT=$(kernel_vm_shift) \ -Bdynamic --export-dynamic --eh-frame-hdr --enable-new-dtags -L$(out)/arch/$(arch) \ $(^:%.ld=-T %.ld) \ - $(linker_archives_options), \ + $(linker_archives_options) $(conf_linker_extra_options), \ LINK loader.elf) @# Build libosv.so matching this loader.elf. This is not a separate @# rule because that caused bug #545. @@ -1978,10 +1986,9 @@ $(out)/kernel.elf: $(stage1_targets) arch/$(arch)/loader.ld $(out)/empty_bootfs. --defsym=OSV_KERNEL_VM_BASE=$(kernel_vm_base) --defsym=OSV_KERNEL_VM_SHIFT=$(kernel_vm_shift) \ -Bdynamic --export-dynamic --eh-frame-hdr --enable-new-dtags -L$(out)/arch/$(arch) \ $(^:%.ld=-T %.ld) \ - $(linker_archives_options), \ + $(linker_archives_options) $(conf_linker_extra_options), \ LINK kernel.elf) $(call quiet, $(STRIP) $(out)/kernel.elf -o $(out)/kernel-stripped.elf, STRIP kernel.elf -> kernel-stripped.elf ) - $(call very-quiet, cp $(out)/kernel-stripped.elf $(out)/kernel.elf) $(out)/bsd/%.o: COMMON += -DSMP -D'__FBSDID(__str__)=extern int __bogus__' diff --git a/conf/base.mk b/conf/base.mk --- a/conf/base.mk +++ b/conf/base.mk @@ -12,3 +12,4 @@ conf-DEBUG_BUILD=0 conf-debug_elf=0 conf_hide_symbols=0 +conf_linker_extra_options= -- You received this message because you are subscribed to the Google Groups "OSv Development" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/osv-dev/000000000000d7bbb205d2ff0560%40google.com.
