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kbuild: Fix TRIM_UNUSED_KSYMS with LTO_CLANG

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With CONFIG_LTO_CLANG, we currently link modules into native
code just before modpost, which means with TRIM_UNUSED_KSYMS
enabled, we still look at the LLVM bitcode in the .o files when
generating the list of used symbols. As the bitcode doesn't
yet have calls to compiler intrinsics and llvm-nm doesn't see
function references that only exist in function-level inline
assembly, we currently need a whitelist for TRIM_UNUSED_KSYMS to
work with LTO.

This change moves module LTO linking to happen earlier, and
thus avoids the issue with LLVM bitcode and TRIM_UNUSED_KSYMS
entirely, allowing us to also drop the whitelist from
gen_autoksyms.sh.

Link: https://github.com/ClangBuiltLinux/linux/issues/1369
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Alexander Lobakin <alobakin@pm.me>
Tested-by: Alexander Lobakin <alobakin@pm.me>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Sami Tolvanen
2021-08-16 11:05:19 -07:00
committed by Masahiro Yamada
parent 7d73c3e9c5
commit 850ded46c6
5 changed files with 38 additions and 51 deletions
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22
scripts/Makefile.modpost
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@@ -41,7 +41,7 @@ __modpost:
include include/config/auto.conf
include $(srctree)/scripts/Kbuild.include
# for ld_flags
# for mod-prelink-ext
include $(srctree)/scripts/Makefile.lib
MODPOST = scripts/mod/modpost \
@@ -118,22 +118,6 @@ $(input-symdump):
@echo >&2 ' Modules may not have dependencies or modversions.'
@echo >&2 ' You may get many unresolved symbol warnings.'
ifdef CONFIG_LTO_CLANG
# With CONFIG_LTO_CLANG, .o files might be LLVM bitcode, so we need to run
# LTO to compile them into native code before running modpost
prelink-ext := .lto
quiet_cmd_cc_lto_link_modules = LTO [M] $@
cmd_cc_lto_link_modules = \
$(LD) $(ld_flags) -r -o $@ \
$(shell [ -s $(@:.lto.o=.o.symversions) ] && \
echo -T $(@:.lto.o=.o.symversions)) \
--whole-archive $^
%.lto.o: %.o
$(call if_changed,cc_lto_link_modules)
endif
modules := $(sort $(shell cat $(MODORDER)))
# KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined symbols
@@ -144,9 +128,9 @@ endif
# Read out modules.order to pass in modpost.
# Otherwise, allmodconfig would fail with "Argument list too long".
quiet_cmd_modpost = MODPOST $@
cmd_modpost = sed 's/\.ko$$/$(prelink-ext)\.o/' $< | $(MODPOST) -T -
cmd_modpost = sed 's/\.ko$$/$(mod-prelink-ext)\.o/' $< | $(MODPOST) -T -
$(output-symdump): $(MODORDER) $(input-symdump) $(modules:.ko=$(prelink-ext).o) FORCE
$(output-symdump): $(MODORDER) $(input-symdump) $(modules:.ko=$(mod-prelink-ext).o) FORCE
$(call if_changed,modpost)
targets += $(output-symdump)