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linux-next/arch/s390/Makefile.postlink

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s390/build: Avoid relocation information in final vmlinux Since commit 778666df60f0 ("s390: compile relocatable kernel without -fPIE") the kernel vmlinux ELF file is linked with --emit-relocs to preserve all relocations, so that all absolute relocations can be extracted using the 'relocs' tool to adjust them during boot. Port and adapt Petr Pavlu's x86 commit 9d9173e9ceb6 ("x86/build: Avoid relocation information in final vmlinux") to s390 to strip all relocations from the final vmlinux ELF file to optimize its size. Following is his original commit message with minor adaptions for s390: The Linux build process on s390 roughly consists of compiling all input files, statically linking them into a vmlinux ELF file, and then taking and turning this file into an actual bzImage bootable file. vmlinux has in this process two main purposes: 1) It is an intermediate build target on the way to produce the final bootable image. 2) It is a file that is expected to be used by debuggers and standard ELF tooling to work with the built kernel. For the second purpose, a vmlinux file is typically collected by various package build recipes, such as distribution spec files, including the kernel's own tar-pkg target. When building the kernel vmlinux contains also relocation information produced by using the --emit-relocs linker option. This is utilized by subsequent build steps to create relocs.S and produce a relocatable image. However, the information is not needed by debuggers and other standard ELF tooling. The issue is then that the collected vmlinux file and hence distribution packages end up unnecessarily large because of this extra data. The following is a size comparison of vmlinux v6.10 with and without the relocation information: | Configuration | With relocs | Stripped relocs | | defconfig | 696 MB | 320 MB | | -CONFIG_DEBUG_INFO | 48 MB | 32 MB | Optimize a resulting vmlinux by adding a postlink step that splits the relocation information into relocs.S and then strips it from the vmlinux binary. Reviewed-by: Vasily Gorbik <gor@linux.ibm.com> Signed-off-by: Jens Remus <jremus@linux.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
2024-08-22 15:30:21 +00:00
# SPDX-License-Identifier: GPL-2.0
# ===========================================================================
# Post-link s390 pass
# ===========================================================================
#
# 1. Separate relocations from vmlinux into relocs.S.
# 2. Strip relocations from vmlinux.
PHONY := __archpost
__archpost:
-include include/config/auto.conf
include $(srctree)/scripts/Kbuild.include
CMD_RELOCS=arch/s390/tools/relocs
OUT_RELOCS = arch/s390/boot
quiet_cmd_relocs = RELOCS $(OUT_RELOCS)/relocs.S
cmd_relocs = \
mkdir -p $(OUT_RELOCS); \
$(CMD_RELOCS) $@ > $(OUT_RELOCS)/relocs.S
quiet_cmd_strip_relocs = RSTRIP $@
cmd_strip_relocs = \
$(OBJCOPY) --remove-section='.rel.*' --remove-section='.rel__*' \
--remove-section='.rela.*' --remove-section='.rela__*' $@
vmlinux: FORCE
$(call cmd,relocs)
$(call cmd,strip_relocs)
clean:
@rm -f $(OUT_RELOCS)/relocs.S
PHONY += FORCE clean
FORCE:
.PHONY: $(PHONY)
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