On Sat, Jan 11, 2025 at 3:33 AM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Fri, 10 Jan 2025 at 10:11, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> >
> > I suppose this is a consequence of 8962b6b475bddc ("kbuild: print
> > short log in addition to the whole command with V=1") which introduced
> > an $(if ) where the else branch is simply ':' and so it always
> > succeeds.
>
> Hmm. Odd. I don't see why that part of the commit exists, and you're
> right, that seems like a bad idea.
>
> And removing that odd $(if..) and making it just do
>
> cmd = @set -e; $($(quiet)log_print) $(delete-on-interrupt) $(cmd_$(1))
>
> doesn't seem to have any obvious negative effects.
When cmd_foo is not defined, $(call if_changed,foo) will fail with this change,
but $(call cmd,foo) will succeed regardless.
In Makefile, the variable expansion works like the latter.
When X is not defined, $(X) is expanded to an empty string successfully.
This is useful.
> I'm probably missing some obvious reason why that $(if..) was added,
> it's been that way for two years now.
We do not need to guard both a definition and its callsite.
For example, the current code in arch/powerpc/Makefile.postlink:
vmlinux: FORCE
@true
ifdef CONFIG_PPC64
$(call cmd,head_check)
endif
ifdef CONFIG_RELOCATABLE
$(call if_changed,relocs_check)
endif
ifdef CONFIG_FUNCTION_TRACER
ifndef CONFIG_PPC64_ELF_ABI_V1
$(call cmd,ftrace_check)
endif
endif
... can be simplified into:
vmlinux: FORCE
$(call cmd,head_check)
$(call if_changed,relocs_check)
$(call cmd,ftrace_check)
--
Best Regards
Masahiro Yamada
