| Message ID | 20200903203053.3411268-12-samitolvanen@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add support for Clang LTO | expand |
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@google.com> 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? > + > +endif # CONFIG_LTO_CLANG > > quiet_cmd_ld_ko_o = LD [M] $@ > - cmd_ld_ko_o = \ > + cmd_ld_ko_o += \ > $(LD) -r $(KBUILD_LDFLAGS) \ > $(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \ > $(addprefix -T , $(KBUILD_LDS_MODULE)) \ > diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh > index 3e99a19b9195..a352a5ad9ef7 100755 > --- a/scripts/link-vmlinux.sh > +++ b/scripts/link-vmlinux.sh > @@ -93,8 +93,29 @@ objtool_link() > { > local objtoolopt; > > + if [ "${CONFIG_LTO_CLANG} ${CONFIG_STACK_VALIDATION}" = "y y" ]; then > + # Don't perform vmlinux validation unless explicitly requested, > + # but run objtool on vmlinux.o now that we have an object file. > + if [ -n "${CONFIG_UNWINDER_ORC}" ]; then > + objtoolopt="orc generate" > + else > + objtoolopt="check" > + fi > + > + if [ -n ${USE_OBJTOOL_MCOUNT} ]; then > + objtoolopt="${objtoolopt} --mcount" > + fi > + fi > + > if [ -n "${CONFIG_VMLINUX_VALIDATION}" ]; then > - objtoolopt="check --vmlinux" > + if [ -z "${objtoolopt}" ]; then > + objtoolopt="check --vmlinux" > + else > + objtoolopt="${objtoolopt} --vmlinux" > + fi > + fi > + > + if [ -n "${objtoolopt}" ]; then > if [ -z "${CONFIG_FRAME_POINTER}" ]; then > objtoolopt="${objtoolopt} --no-fp" > fi > -- > 2.28.0.402.g5ffc5be6b7-goog >
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@google.com> > > 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
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 + +endif # CONFIG_LTO_CLANG quiet_cmd_ld_ko_o = LD [M] $@ - cmd_ld_ko_o = \ + cmd_ld_ko_o += \ $(LD) -r $(KBUILD_LDFLAGS) \ $(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \ $(addprefix -T , $(KBUILD_LDS_MODULE)) \ diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh index 3e99a19b9195..a352a5ad9ef7 100755 --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -93,8 +93,29 @@ objtool_link() { local objtoolopt; + if [ "${CONFIG_LTO_CLANG} ${CONFIG_STACK_VALIDATION}" = "y y" ]; then + # Don't perform vmlinux validation unless explicitly requested, + # but run objtool on vmlinux.o now that we have an object file. + if [ -n "${CONFIG_UNWINDER_ORC}" ]; then + objtoolopt="orc generate" + else + objtoolopt="check" + fi + + if [ -n ${USE_OBJTOOL_MCOUNT} ]; then + objtoolopt="${objtoolopt} --mcount" + fi + fi + if [ -n "${CONFIG_VMLINUX_VALIDATION}" ]; then - objtoolopt="check --vmlinux" + if [ -z "${objtoolopt}" ]; then + objtoolopt="check --vmlinux" + else + objtoolopt="${objtoolopt} --vmlinux" + fi + fi + + if [ -n "${objtoolopt}" ]; then if [ -z "${CONFIG_FRAME_POINTER}" ]; then objtoolopt="${objtoolopt} --no-fp" fi
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@google.com> --- arch/Kconfig | 2 +- scripts/Makefile.build | 2 ++ scripts/Makefile.modfinal | 24 ++++++++++++++++++++++-- scripts/link-vmlinux.sh | 23 ++++++++++++++++++++++- 4 files changed, 47 insertions(+), 4 deletions(-)