On Wed, Aug 11, 2021 at 01:30:35PM -0700, Sami Tolvanen 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(-) Cool; this looks good. (It even makes the code smaller.) I can take this in my tree if you'd rather not carry it Masahiro? -Kees > 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) > +endif > + > cmd_mod = { \ > echo $(if $($*-objs)$($*-y)$($*-m), $(addprefix $(obj)/, $($*-objs) $($*-y) $($*-m)), $(@:.mod=.o)); \ > $(undefined_syms) echo; \ > } > $@ > > -$(obj)/%.mod: $(obj)/%.o FORCE > +$(obj)/%.mod: $(obj)/%$(mod-prelink-ext).o FORCE > $(call if_changed,mod) > > quiet_cmd_cc_lst_c = MKLST $@ > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib > index 10950559b223..af1c920a585c 100644 > --- a/scripts/Makefile.lib > +++ b/scripts/Makefile.lib > @@ -225,6 +225,13 @@ dtc_cpp_flags = -Wp,-MMD,$(depfile).pre.tmp -nostdinc \ > $(addprefix -I,$(DTC_INCLUDE)) \ > -undef -D__DTS__ > > +ifeq ($(CONFIG_LTO_CLANG),y) > +# With CONFIG_LTO_CLANG, .o files in modules might be LLVM bitcode, so we > +# need to run LTO to compile them into native code (.lto.o) before further > +# processing. > +mod-prelink-ext := .lto > +endif > + > # Objtool arguments are also needed for modfinal with LTO, so we define > # then here to avoid duplication. > objtool_args = \ > diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal > index 5e9b8057fb24..ff805777431c 100644 > --- a/scripts/Makefile.modfinal > +++ b/scripts/Makefile.modfinal > @@ -9,7 +9,7 @@ __modfinal: > include include/config/auto.conf > include $(srctree)/scripts/Kbuild.include > > -# for c_flags and objtool_args > +# for c_flags and mod-prelink-ext > include $(srctree)/scripts/Makefile.lib > > # find all modules listed in modules.order > @@ -30,23 +30,6 @@ quiet_cmd_cc_o_c = CC [M] $@ > > ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink) > > -ifdef CONFIG_LTO_CLANG > -# With CONFIG_LTO_CLANG, reuse the object file we compiled for modpost to > -# avoid a second slow LTO link > -prelink-ext := .lto > - > -# ELF processing was skipped earlier because we didn't have native code, > -# so let's now process the prelinked binary before we link the module. > - > -ifdef CONFIG_STACK_VALIDATION > -cmd_ld_ko_o += \ > - $(objtree)/tools/objtool/objtool $(objtool_args) \ > - $(@:.ko=$(prelink-ext).o); > - > -endif # CONFIG_STACK_VALIDATION > - > -endif # CONFIG_LTO_CLANG > - > quiet_cmd_ld_ko_o = LD [M] $@ > cmd_ld_ko_o += \ > $(LD) -r $(KBUILD_LDFLAGS) \ > @@ -72,7 +55,7 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check), \ > > > # Re-generate module BTFs if either module's .ko or vmlinux changed > -$(modules): %.ko: %$(prelink-ext).o %.mod.o scripts/module.lds $(if $(KBUILD_BUILTIN),vmlinux) FORCE > +$(modules): %.ko: %$(mod-prelink-ext).o %.mod.o scripts/module.lds $(if $(KBUILD_BUILTIN),vmlinux) FORCE > +$(call if_changed_except,ld_ko_o,vmlinux) > ifdef CONFIG_DEBUG_INFO_BTF_MODULES > +$(if $(newer-prereqs),$(call cmd,btf_ko)) > diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost > index c383ba33d837..eef56d629799 100644 > --- a/scripts/Makefile.modpost > +++ b/scripts/Makefile.modpost > @@ -41,7 +41,7 @@ __modpost: > include include/config/auto.conf > include $(srctree)/scripts/Kbuild.include > > -# for ld_flags > +# for mod-prelink-ext > include $(srctree)/scripts/Makefile.lib > > MODPOST = scripts/mod/modpost \ > @@ -118,22 +118,6 @@ $(input-symdump): > @echo >&2 ' Modules may not have dependencies or modversions.' > @echo >&2 ' You may get many unresolved symbol warnings.' > > -ifdef CONFIG_LTO_CLANG > -# With CONFIG_LTO_CLANG, .o files might be LLVM bitcode, so we need to run > -# LTO to compile them into native code before running modpost > -prelink-ext := .lto > - > -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 $^ > - > -%.lto.o: %.o > - $(call if_changed,cc_lto_link_modules) > -endif > - > modules := $(sort $(shell cat $(MODORDER))) > > # KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined symbols > @@ -144,9 +128,9 @@ endif > # Read out modules.order to pass in modpost. > # Otherwise, allmodconfig would fail with "Argument list too long". > quiet_cmd_modpost = MODPOST $@ > - cmd_modpost = sed 's/\.ko$$/$(prelink-ext)\.o/' $< | $(MODPOST) -T - > + cmd_modpost = sed 's/\.ko$$/$(mod-prelink-ext)\.o/' $< | $(MODPOST) -T - > > -$(output-symdump): $(MODORDER) $(input-symdump) $(modules:.ko=$(prelink-ext).o) FORCE > +$(output-symdump): $(MODORDER) $(input-symdump) $(modules:.ko=$(mod-prelink-ext).o) FORCE > $(call if_changed,modpost) > > targets += $(output-symdump) > diff --git a/scripts/gen_autoksyms.sh b/scripts/gen_autoksyms.sh > index da320151e7c3..6ed0d225c8b1 100755 > --- a/scripts/gen_autoksyms.sh > +++ b/scripts/gen_autoksyms.sh > @@ -26,18 +26,6 @@ if [ -n "$CONFIG_MODVERSIONS" ]; then > needed_symbols="$needed_symbols module_layout" > fi > > -# With CONFIG_LTO_CLANG, LLVM bitcode has not yet been compiled into a binary > -# when the .mod files are generated, which means they don't yet contain > -# references to certain symbols that will be present in the final binaries. > -if [ -n "$CONFIG_LTO_CLANG" ]; then > - # intrinsic functions > - needed_symbols="$needed_symbols memcpy memmove memset" > - # ftrace > - needed_symbols="$needed_symbols _mcount" > - # stack protector symbols > - needed_symbols="$needed_symbols __stack_chk_fail __stack_chk_guard" > -fi > - > ksym_wl= > if [ -n "$CONFIG_UNUSED_KSYMS_WHITELIST" ]; then > # Use 'eval' to expand the whitelist path and check if it is relative > > base-commit: 761c6d7ec820f123b931e7b8ef7ec7c8564e450f > -- > 2.32.0.605.g8dce9f2422-goog > -- Kees Cook
