Re: [PATCH 05/22] kbuild: lto: postpone objtool

[Peter Zijlstra]

On Wed, Jun 24, 2020 at 02:49:25PM -0700, Sami Tolvanen wrote:
> On Wed, Jun 24, 2020 at 11:19:08PM +0200, Peter Zijlstra wrote:
> > On Wed, Jun 24, 2020 at 01:31:43PM -0700, Sami Tolvanen wrote:
> > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> > > index 30827f82ad62..12b115152532 100644
> > > --- a/include/linux/compiler.h
> > > +++ b/include/linux/compiler.h
> > > @@ -120,7 +120,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> > >  /* Annotate a C jump table to allow objtool to follow the code flow */
> > >  #define __annotate_jump_table __section(.rodata..c_jump_table)
> > >  
> > > -#ifdef CONFIG_DEBUG_ENTRY
> > > +#if defined(CONFIG_DEBUG_ENTRY) || defined(CONFIG_LTO_CLANG)
> > >  /* Begin/end of an instrumentation safe region */
> > >  #define instrumentation_begin() ({					\
> > >  	asm volatile("%c0:\n\t"						\
> > 
> > Why would you be doing noinstr validation for lto builds? That doesn't
> > make sense.
> 
> This is just to avoid a ton of noinstr warnings when we run objtool on
> vmlinux.o, but I'm also fine with skipping noinstr validation with LTO.

Right, then we need to make --no-vmlinux work properly when
!DEBUG_ENTRY, which I think might be buggered due to us overriding the
argument when the objname ends with "vmlinux.o".

> > > +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,)			\
> > > +		$(@:.ko=$(prelink-ext).o);
> > > +
> > > +endif # SKIP_STACK_VALIDATION
> > > +endif # CONFIG_STACK_VALIDATION
> > 
> > What about the objtool invocation from link-vmlinux.sh ?
> 
> What about it? The existing objtool_link invocation in link-vmlinux.sh
> works fine for our purposes as well.

Well, I was wondering why you're adding yet another objtool invocation
while we already have one.