From: Sami Tolvanen <samitolvanen@xxxxxxxxxx> Date: Fri, 16 Jul 2021 16:18:42 -0700 > Hi Al, > > On Fri, Jul 16, 2021 at 4:00 PM Alexander Lobakin <alobakin@xxxxx> wrote: > > > > From: Sami Tolvanen <samitolvanen@xxxxxxxxxx> > > Date: Fri, 16 Jul 2021 13:45:45 -0700 > > > > > 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> > > > --- > > > scripts/Makefile.build | 25 ++++++++++++++++++++++++- > > > scripts/Makefile.lib | 7 +++++++ > > > scripts/Makefile.modfinal | 21 ++------------------- > > > scripts/Makefile.modpost | 22 +++------------------- > > > scripts/gen_autoksyms.sh | 12 ------------ > > > 5 files changed, 36 insertions(+), 51 deletions(-) > > > > > > diff --git a/scripts/Makefile.build b/scripts/Makefile.build > > > index 10b2f2380d6f..80e0fa810870 100644 > > > --- a/scripts/Makefile.build > > > +++ b/scripts/Makefile.build > > > @@ -202,6 +202,7 @@ sub_cmd_record_mcount = \ > > > if [ $(@) != "scripts/mod/empty.o" ]; then \ > > > $(objtree)/scripts/recordmcount $(RECORDMCOUNT_FLAGS) "$(@)"; \ > > > fi; > > > +/ > > > > Seems like a leftover or a random typo here. > > Oops, indeed. > > > > recordmcount_source := $(srctree)/scripts/recordmcount.c \ > > > $(srctree)/scripts/recordmcount.h > > > else > > > @@ -271,12 +272,34 @@ $(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) \ > > > > Now $(part-of-module) inside $(objtool_args) doesn't get expanded > > properly, because previously it was being called on x.ko, and now > > it's being called on x.lto.o. $(basename $@) returns "x.lto" instead > > of "x", and Make doesn't find "x.lto.o" in $(real-objs-m). To be more precise: Previously, objtool was being called from Makefile.modfinal, where part-of-module is hardcoded to 'y'. Now it's being called from Makefile.build, and part-of-module is being calculated the same way as for non-LTO build (when objtool is being called on each object file rather than final composite object). So, part-of-module and objtool invocation is now correct for modules with single source file, but wrong for multi-object modules. The simplest fix is to append '--module' to objtool args unconditionally when we're trying to process .lto.o file. > > An example of objtool args dump: > > > > LTO [M] fs/btrfs/btrfs.lto.o > > Call: ./tools/objtool/objtool orc generate --no-fp --no-unreachable --retpoline --uaccess fs/btrfs/btrfs.lto.o > > fs/btrfs/btrfs.lto.o: warning: objtool: static_call: can't find static_call_key symbol: __SCK__might_resched > > Curiously I didn't see objtool warnings when building allmodconfig, > but you're obviously correct here. I'll fix this in v2. > > > As can be seen, objtools command line no longer contains "--module". > > And this warning about "can't find static_call_key" can appear only > > in case of !module -> no -m|--module param was given. > > > > As a result, modules get broken and the kernel panics after loading > > initramfs. > > Thanks for taking a look! > > Sami Thanks for working on ClangLTO/CFI! Al
