On Thu, Aug 19, 2021 at 12:06 AM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote: > > On Tue, Aug 17, 2021 at 7:34 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote: > > > > 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 $@ > > Good catch, probably a leftover from an earlier iteration. > > > Shall I fix it locally unless > > I find more questionable code? > > Please do. > > Sami Applied with $(@:.ko=.lto.o) -> $@ Thanks. -- Best Regards Masahiro Yamada
