[PATCH v3 06/15] kbuild: record symbol versions in *.cmd files

Masahiro Yamada
2022-05-05T07:31:48Z

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>
---

(no changes since v2)

Changes in v2:
- Fix CONFIG_MODULE_REL_CRCS=y case

scripts/Makefile.build | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index f6a506318795..a1023868775f 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -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
--
2.32.0