On Thu, Aug 12, 2021 at 5:30 AM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote: > > 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@xxxxxxxxxx> > Reviewed-by: Alexander Lobakin <alobakin@xxxxx> > Tested-by: Alexander Lobakin <alobakin@xxxxx> > --- > Changes in v2: > - Fixed a couple of typos. > - Fixed objtool arguments for .lto.o to always include --module. > > --- > scripts/Makefile.build | 24 +++++++++++++++++++++++- > scripts/Makefile.lib | 7 +++++++ > scripts/Makefile.modfinal | 21 ++------------------- > scripts/Makefile.modpost | 22 +++------------------- > scripts/gen_autoksyms.sh | 12 ------------ > 5 files changed, 35 insertions(+), 51 deletions(-) > > diff --git a/scripts/Makefile.build b/scripts/Makefile.build > index 02197cb8e3a7..778dabea3a89 100644 > --- a/scripts/Makefile.build > +++ b/scripts/Makefile.build > @@ -271,12 +271,34 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) $$(objtool_dep) FORCE > $(call if_changed_rule,cc_o_c) > $(call cmd,force_checksrc) > > +ifdef CONFIG_LTO_CLANG > +# Module .o files may contain LLVM bitcode, compile them into native code > +# before ELF processing > +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 $^ > + > +ifdef CONFIG_STACK_VALIDATION > +# objtool was skipped for LLVM bitcode, run it now that we have compiled > +# modules into native code > +cmd_cc_lto_link_modules += ; \ > + $(objtree)/tools/objtool/objtool $(objtool_args) --module \ > + $(@:.ko=$(mod-prelink-ext).o) > +endif > + > +$(obj)/%.lto.o: $(obj)/%.o > + $(call if_changed,cc_lto_link_modules) Documentation/kbuild/makefiles.rst says: Note: It is a typical mistake to forget the FORCE prerequisite. The current code in scripts/Makefile.modpost is also wrong, though. -- Best Regards Masahiro Yamada
