On Tue, Aug 17, 2021 at 3:05 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 v4: > - Added .lto.o to targets to actually fix the use of if_changed. > - Replaced an unnecessary mod-prelink-ext with .lto. > > Changes in v3: > - Added missing FORCE. > > Changes in v2: > - Fixed a couple of typos. > - Fixed objtool arguments for .lto.o to always include --module. > > --- > scripts/Makefile.build | 28 +++++++++++++++++++++++++++- > scripts/Makefile.lib | 7 +++++++ > scripts/Makefile.modfinal | 21 ++------------------- > scripts/Makefile.modpost | 22 +++------------------- > scripts/gen_autoksyms.sh | 12 ------------ > 5 files changed, 39 insertions(+), 51 deletions(-) > > diff --git a/scripts/Makefile.build b/scripts/Makefile.build > index 02197cb8e3a7..a6f43afd09bb 100644 > --- a/scripts/Makefile.build > +++ b/scripts/Makefile.build > @@ -88,6 +88,10 @@ endif > > targets-for-modules := $(patsubst %.o, %.mod, $(filter %.o, $(obj-m))) > > +ifdef CONFIG_LTO_CLANG > +targets-for-modules += $(patsubst %.o, %.lto.o, $(filter %.o, $(obj-m))) > +endif > + > ifdef need-modorder > targets-for-modules += $(obj)/modules.order > endif > @@ -271,12 +275,34 @@ $(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 $(filter-out FORCE,$^) > + > +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 \ > + $(@:.ko=.lto.o) What is this "$(@:.ko=.lto.o)" doing ? The target is already suffixed with .lto.o so $(@:.ko=.lto.o) should be the same as $@ Shall I fix it locally unless I find more questionable code? > +endif > + > +$(obj)/%.lto.o: $(obj)/%.o FORCE > + $(call if_changed,cc_lto_link_modules) > +endif > + -- Best Regards Masahiro Yamada
