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kbuild: record symbol versions in *.cmd files

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When CONFIG_MODVERSIONS=y, the output from genksyms is saved in
separate *.symversions files, and will be used much later when
CONFIG_LTO_CLANG=y because it is impossible to update LLVM bit code
here.

This approach is not robust because:

 - *.symversions may or may not exist. If *.symversions does not
   exist, we never know if it is missing for legitimate reason
   (i.e. no EXPORT_SYMBOL) or something bad has happened (for
   example, the user accidentally deleted it). Once it occurs,
   it is not self-healing because *.symversions is generated
   as a side effect.

 - stale (i.e. invalid) *.symversions might be picked up if an
   object is generated in a non-ordinary way, and corresponding
   *.symversions (, which was generated by old builds) just happen
   to exist.

A more robust approach is to save symbol versions in *.cmd files
because:

 - *.cmd always exists (if the object is generated by if_changed
   rule or friends). Even if the user accidentally deletes it,
   it will be regenerated in the next build.

 - *.cmd is always re-generated when the object is updated. This
   avoid stale version information being picked up.

I will remove *.symversions later.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Tested-by: Nathan Chancellor <nathan@kernel.org>
This commit is contained in:
Masahiro Yamada 2022-05-05 16:22:35 +09:00
parent e493f47275
commit 78e9e56af3
1 changed files with 7 additions and 0 deletions
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7
scripts/Makefile.build
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@ -171,10 +171,17 @@ ifdef CONFIG_MODVERSIONS
# Generate .o.symversions files for each .o with exported symbols, and link these
# to the kernel and/or modules at the end.
genksyms_format_rel_crc := [^_]*__crc_\([^ ]*\) = \.; LONG(\([^)]*\)).*
genksyms_format_normal := __crc_\(.*\) = \(.*\);
genksyms_format := $(if $(CONFIG_MODULE_REL_CRCS),$(genksyms_format_rel_crc),$(genksyms_format_normal))
gen_symversions = \
if $(NM) $@ 2>/dev/null | grep -q __ksymtab; then \
$(call cmd_gensymtypes_$(1),$(KBUILD_SYMTYPES),$(@:.o=.symtypes)) \
> $@.symversions; \
sed -n 's/$(genksyms_format)/$(pound)SYMVER \1 \2/p' $@.symversions \
>> $(dot-target).cmd; \
else \
rm -f $@.symversions; \
fi