linux-kernel - Re: [PATCH] efi/libstub: avoid linking libstub/lib-ksyms.o into vmlinux

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Message-ID: <CAK7LNATwBALmPjZiY6teac3FcA_BFsBVzwf5cqbVNCZSqGrHJg@mail.gmail.com>
Date:   Thu, 5 Mar 2020 16:39:06 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] efi/libstub: avoid linking libstub/lib-ksyms.o into vmlinux

On Thu, Mar 5, 2020 at 4:21 PM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Thu, 5 Mar 2020 at 06:50, Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > drivers/firmware/efi/libstub/Makefile is supposed to create a static
> > library, which is not directly linked to vmlinux.
> >
>
> This is not true for arm64. Does that matter?



Yeah, I know.  arm64 vmlinux links it
(but in a different manner from normal lib.a )


Shall I rephrase this paragraph as follows?

drivers/firmware/efi/libstub/Makefile is supposed to create a static
library, which is not directly linked to vmlinux on ARCH=arm, x86.



This is just a matter of whether linking
unneeded lib-ksyms.o or not.





> > Since commit 7f2084fa55e6 ("[kbuild] handle exports in lib-y objects
> > reliably"), any Makefile using lib-y generates lib-ksyms.o which is
> > linked into vmlinux.
> >
> > In this case, the following garbage object is linked into vmlinux.
> >
> >   drivers/firmware/efi/libstub/lib-ksyms.o
> >
> > We do not want to link anything from libstub/ directly to vmlinux,
> > so using subdir-y instead of obj-y is the correct way to descend into
> > this directory.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
> >
> >  drivers/firmware/efi/Makefile | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
> > index 554d795270d9..4fd2fa02f549 100644
> > --- a/drivers/firmware/efi/Makefile
> > +++ b/drivers/firmware/efi/Makefile
> > @@ -19,7 +19,7 @@ obj-$(CONFIG_EFI_VARS_PSTORE)         += efi-pstore.o
> >  obj-$(CONFIG_UEFI_CPER)                        += cper.o
> >  obj-$(CONFIG_EFI_RUNTIME_MAP)          += runtime-map.o
> >  obj-$(CONFIG_EFI_RUNTIME_WRAPPERS)     += runtime-wrappers.o
> > -obj-$(CONFIG_EFI_STUB)                 += libstub/
> > +subdir-$(CONFIG_EFI_STUB)              += libstub
> >  obj-$(CONFIG_EFI_FAKE_MEMMAP)          += fake_map.o
> >  obj-$(CONFIG_EFI_BOOTLOADER_CONTROL)   += efibc.o
> >  obj-$(CONFIG_EFI_TEST)                 += test/
> > --
> > 2.17.1
> >



-- 
Best Regards
Masahiro Yamada