linux-kernel - Re: [RFC PATCH 2/3] x86/boot/compressed: force hidden visibility for all symbol references

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Message-ID: <CAKv+Gu_EVuX1nktX6Ueyot7XFgtq+AG9SqRHvN91r9oG5GL_wQ@mail.gmail.com>
Date:   Wed, 8 Jan 2020 17:47:57 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC PATCH 2/3] x86/boot/compressed: force hidden visibility for
 all symbol references

On Wed, 8 Jan 2020 at 16:57, Arvind Sankar <nivedita@...m.mit.edu> wrote:
>
> On Wed, Jan 08, 2020 at 04:47:51PM +0100, Ard Biesheuvel wrote:
> > The EFI stub already sets the hidden visibility attribute for the few
> > external symbol references that it contains, so it is not needed in
> > the context of this series.
> >
> > In the future, we can revisit this if we want to get rid of the
> > various __pure getter functions, but that requires thorough testing on
> > other architectures and toolchains, so I'd prefer to leave that for
> > later.
>
> We don't need it for the stub right now, but then this bit in the cover
> letter is not yet true, we still need to be careful about libstub code.
>
> > ...we can start using ordinary external symbol references in the EFI
> > stub without running the risk of boot regressions.

Spurious GOT entries will now be caught by the ASSERT() in the linker
script and fail the build instead of causing hard to debug boot
regressions, so it is not entirely untrue either. But I take your
point.