On Thu, Sep 03, 2020 at 03:19:43PM -0700, Kees Cook wrote: > On Thu, Sep 03, 2020 at 01:30:36PM -0700, Sami Tolvanen wrote: > > With LTO, LLVM bitcode won't be compiled into native code until > > modpost_link, or modfinal for modules. This change postpones calls > > to objtool until after these steps. > > > > Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx> > > For a "fail fast" style of building, it makes sense to have objtool run > as early as possible, so it makes sense to keep the current behavior in > non-LTO mode. I do wonder, though, if there is a real benefit to having > "fail fast" case. I imagine a lot of automated builds are using > --keep-going with make, and actually waiting until the end to do the > validation means more code will get build-tested before objtool rejects > the results. *shrug* > > > --- > > arch/Kconfig | 2 +- > > scripts/Makefile.build | 2 ++ > > scripts/Makefile.modfinal | 24 ++++++++++++++++++++++-- > > scripts/link-vmlinux.sh | 23 ++++++++++++++++++++++- > > 4 files changed, 47 insertions(+), 4 deletions(-) > > > > diff --git a/arch/Kconfig b/arch/Kconfig > > index 71392e4a8900..7a418907e686 100644 > > --- a/arch/Kconfig > > +++ b/arch/Kconfig > > @@ -599,7 +599,7 @@ config LTO_CLANG > > depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm) > > depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm) > > depends on ARCH_SUPPORTS_LTO_CLANG > > - depends on !FTRACE_MCOUNT_RECORD > > + depends on HAVE_OBJTOOL_MCOUNT || !(X86_64 && DYNAMIC_FTRACE) > > depends on !KASAN > > depends on !GCOV_KERNEL > > select LTO > > diff --git a/scripts/Makefile.build b/scripts/Makefile.build > > index c348e6d6b436..b8f1f0d65a73 100644 > > --- a/scripts/Makefile.build > > +++ b/scripts/Makefile.build > > @@ -218,6 +218,7 @@ cmd_record_mcount = $(if $(findstring $(strip $(CC_FLAGS_FTRACE)),$(_c_flags)), > > endif # USE_RECORDMCOUNT > > > > ifdef CONFIG_STACK_VALIDATION > > +ifndef CONFIG_LTO_CLANG > > ifneq ($(SKIP_STACK_VALIDATION),1) > > > > __objtool_obj := $(objtree)/tools/objtool/objtool > > @@ -253,6 +254,7 @@ objtool_obj = $(if $(patsubst y%,, \ > > $(__objtool_obj)) > > > > endif # SKIP_STACK_VALIDATION > > +endif # CONFIG_LTO_CLANG > > endif # CONFIG_STACK_VALIDATION > > > > # Rebuild all objects when objtool changes, or is enabled/disabled. > > diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal > > index 1005b147abd0..909bd509edb4 100644 > > --- a/scripts/Makefile.modfinal > > +++ b/scripts/Makefile.modfinal > > @@ -34,10 +34,30 @@ ifdef CONFIG_LTO_CLANG > > # With CONFIG_LTO_CLANG, reuse the object file we compiled for modpost to > > # avoid a second slow LTO link > > prelink-ext := .lto > > -endif > > + > > +# ELF processing was skipped earlier because we didn't have native code, > > +# so let's now process the prelinked binary before we link the module. > > + > > +ifdef CONFIG_STACK_VALIDATION > > +ifneq ($(SKIP_STACK_VALIDATION),1) > > +cmd_ld_ko_o += \ > > + $(objtree)/tools/objtool/objtool \ > > + $(if $(CONFIG_UNWINDER_ORC),orc generate,check) \ > > + --module \ > > + $(if $(CONFIG_FRAME_POINTER),,--no-fp) \ > > + $(if $(CONFIG_GCOV_KERNEL),--no-unreachable,) \ > > + $(if $(CONFIG_RETPOLINE),--retpoline,) \ > > + $(if $(CONFIG_X86_SMAP),--uaccess,) \ > > + $(if $(USE_OBJTOOL_MCOUNT),--mcount,) \ > > + $(@:.ko=$(prelink-ext).o); > > + > > +endif # SKIP_STACK_VALIDATION > > +endif # CONFIG_STACK_VALIDATION > > I wonder if objtool_args could be reused here instead of having two > places to keep in sync? It looks like that might mean moving things > around a bit before this patch, since I can't quite see if > Makefile.build's variables are visible to Makefile.modfinal? It doesn't look like they are. I suppose we could move objtool_args to Makefile.lib. Masahiro, any thoughts? Sami
