Re: Tool directory build problem..

[Nathan Chancellor <nathan@kernel.org>]

Hi Linus,

On Sat, Sep 27, 2025 at 11:23:22AM -0700, Linus Torvalds wrote:
> It doesn't work for that pfrut tool because the top-level Makefile
> rule does this:
> 
>     $(Q)$(MAKE) LDFLAGS= O=$(abspath $(objtree)) subdir=tools -C
> $(srctree)/tools/ $*
> 
> and that "LDFLAGS=" is an overriding variable assignment, so the use of
> 
>     LDFLAGS += -luuid
> 
> in tools/power/acpi/tools/pfrut/Makefile end sup not working.
> 
> But it works in all other situations, just not when build this way
> from the top. Annoying.
> 
> I'm not sure *why* the top-level Makefile does that "LDFLAGS="
> override thing. It doesn't do it for anything else. Just that LDFLAGS
> variable.
> 
> Yes, yes, the ACPI tool makefile could then use
> 
>     override LDFLAGS += -luuid
> 
> but why would it do something as crazy as that?
> 
> That "LDFLAGS=" override goes back many many years,  In fact, it goes
> back to the very initial addition of those rules in commit
> ea01fa9f63ae ("tools: Connect to the kernel build system").
> 
> So I have no idea why it exists. Just removing the "LDFLAGS=" override
> seems to fix everything for me, but I must be missing something.

It looks like prior to commit d503ac531a52 ("kbuild: rename LDFLAGS to
KBUILD_LDFLAGS") in 4.19, LDFLAGS was used throughout Kbuild so I
suspect that LDFLAGS= was there to avoid poluting the tools build with
the flags from the main kernel build. Given the rename, it seems like
you should be able to remove LDFLAGS= from the tools target without any
problems.

I generally agree with Masahiro's prior comments around the tools/ build
system (especially hooking into it for the main kernel build) but I do
not see a good reason to break the tools/% target patterns if they are
not overly broken or hard to maintain :)

Cheers,
Nathan