Re: [PATCH] powerpc: remove meaningless KBUILD_ARFLAGS addition

On Thu, Jul 18, 2019 at 1:46 AM Segher Boessenkool
[off-list ref] wrote:

On Thu, Jul 18, 2019 at 12:19:36AM +0900, Masahiro Yamada wrote:

quoted

On Wed, Jul 17, 2019 at 11:38 PM Segher Boessenkool
[off-list ref] wrote:

quoted

On Tue, Jul 16, 2019 at 10:15:47PM +1000, Michael Ellerman wrote:

quoted

Segher Boessenkool [off-list ref] writes:
And it's definitely calling ar with no flags, eg:

  rm -f init/built-in.a; powerpc-linux-ar rcSTPD init/built-in.a init/main.o init/version.o init/do_mounts.o init/do_mounts_rd.o init/do_mounts_initrd.o init/do_mounts_md.o init/initramfs.o init/init_task.o

This uses thin archives.  Those will work fine.

The failing case was empty files IIRC, stuff created from no inputs.

Actually, empty files are created everywhere.

quoted

       cmd_ar_builtin = rm -f $@; $(AR) rcSTP$(KBUILD_ARFLAGS) $@
$(real-prereqs)

You use thin archives.

Does every config use thin archives always nowadays?

Kbuild always uses thin archives as far as vmlinux is concerned.

But, there are some other call-sites.

masahiro@pug:~/ref/linux$ git grep  '$(AR)' -- :^Documentation :^tools
arch/powerpc/boot/Makefile:    BOOTAR := $(AR)
arch/unicore32/lib/Makefile:    $(Q)$(AR) p $(GNU_LIBC_A) $(notdir $@) > $@
arch/unicore32/lib/Makefile:    $(Q)$(AR) p $(GNU_LIBGCC_A) $(notdir $@) > $@
lib/raid6/test/Makefile:         $(AR) cq $@ $^
scripts/Kbuild.include:ar-option = $(call try-run, $(AR) rc$(1)
"$$TMP",$(1),$(2))
scripts/Makefile.build:      cmd_ar_builtin = rm -f $@; $(AR)
rcSTP$(KBUILD_ARFLAGS) $@ $(real-prereqs)
scripts/Makefile.lib:      cmd_ar = rm -f $@; $(AR)
rcsTP$(KBUILD_ARFLAGS) $@ $(real-prereqs)


Probably, you are interested in arch/powerpc/boot/Makefile.
This does not seem a thin archive.

quoted

BTW, your commit 8995ac8702737147115e1c75879a1a2d75627b9e
dates back to 2008.

At that time, thin archive was not used.

Yes, I know.  This isn't about built-in.[oa], it is about *other*
archives we at least *used to* create.  If we *know* we do not anymore,
then this workaround can of course be removed (and good riddance).

If it is not about built-in.[oa],
which archive are you talking about?

Can you pin-point the one?

masahiro@pug:~/ref/linux$ git log --oneline  -1
8995ac870273 (HEAD) [POWERPC] Specify GNUTARGET on $(AR) invocations
masahiro@pug:~/ref/linux$ git grep '(AR)'
Documentation/kbuild/makefiles.txt:     per-directory options to $(LD)
and $(AR).
arch/powerpc/Makefile:CROSS32AR := GNUTARGET=elf32-powerpc $(AR)
arch/powerpc/Makefile:override AR       := GNUTARGET=elf$(SZ)-powerpc $(AR)
drivers/md/raid6test/Makefile:   $(AR) cq $@ $^
scripts/Makefile.build:               rm -f $@; $(AR) rcs $@)
scripts/Makefile.build:cmd_link_l_target = rm -f $@; $(AR)
$(EXTRA_ARFLAGS) rcs $@ $(lib-y)
masahiro@pug:~/ref/linux$ git grep '(CROSS32AR)'
arch/powerpc/boot/Makefile:      cmd_bootar = $(CROSS32AR) -cr $@.$$$$
$(filter-out FORCE,$^); mv $@.$$$$ $@

If ar creates an archive file (a real one, not a thin archive), and it
has no input files, it uses its default object format as destination
format, if it isn't told to use something else.  And that doesn't work,
it needs to use some format compatible with what that archive later is
linked with.

I compile-tested v4.10, which was before the thin-archive migration,
but I did not see any problem for building ppc32/64.

Whether or not it is a thin archive,
an empty archive is always 8-byte file.

masahiro@pug:~/ref/linux$ cat kernel/livepatch/built-in.o
!<arch>

Is there a room for caring about the under-lying architecture?


-- 
Best Regards
Masahiro Yamada