| Message ID | 20220424190811.1678416-22-masahiroy@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kbuild: yet another series of cleanups (modpost and LTO) | expand |
On ma. 25. april 2022 kl. 04.08 +0000 Masahiro Yamada wrote: > 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 of the build rule of the object. > > - 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> > --- > > scripts/Makefile.build | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/scripts/Makefile.build b/scripts/Makefile.build > index f6a506318795..e03e85c90b26 100644 > --- a/scripts/Makefile.build > +++ b/scripts/Makefile.build > @@ -175,6 +175,8 @@ gen_symversions = \ > if $(NM) $@ 2>/dev/null | grep -q __ksymtab; then \ > $(call cmd_gensymtypes_$(1),$(KBUILD_SYMTYPES),$(@:.o=.symtypes)) \ > > $@.symversions; \ > + echo >> $(dot-target).cmd ; \ > + sed 's/\(.*\) = \(.*\);/$(pound)\1=\2/' $@.symversions >> $(dot-target).cmd ; \ > else \ > rm -f $@.symversions; \ > fi While reviewing this patch, I was missing the update of the comment a few lines above. But I understand that it makes more sense to update it in the follow-up patch. Tested-by: Nicolas Schier <nicolas@fjasle.eu> Reviewed-by: Nicolas Schier <nicolas@fjasle.eu> > -- > 2.32.0
diff --git a/scripts/Makefile.build b/scripts/Makefile.build index f6a506318795..e03e85c90b26 100644 --- a/scripts/Makefile.build +++ b/scripts/Makefile.build @@ -175,6 +175,8 @@ gen_symversions = \ if $(NM) $@ 2>/dev/null | grep -q __ksymtab; then \ $(call cmd_gensymtypes_$(1),$(KBUILD_SYMTYPES),$(@:.o=.symtypes)) \ > $@.symversions; \ + echo >> $(dot-target).cmd ; \ + sed 's/\(.*\) = \(.*\);/$(pound)\1=\2/' $@.symversions >> $(dot-target).cmd ; \ else \ rm -f $@.symversions; \ fi
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 of the build rule of the object. - 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> --- scripts/Makefile.build | 2 ++ 1 file changed, 2 insertions(+)