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

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Date:   Thu, 5 Mar 2020 08:47:15 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Masahiro Yamada <masahiroy@...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, 5 Mar 2020 at 08:39, Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> 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.
>

How about

"""
drivers/firmware/efi/libstub/Makefile builds a static library, which
is not linked into the main vmlinux target in the ordinary way
[arm64], or at all [ARM, x86]
"""



>
>
>
>
> > > 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,

and

"""
We do not want to follow the default linking rules for static
libraries built under libstub/
"""

If you agree, no need to resend, I'll fix it up when applying


> > > 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