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From: Arvind Sankar <nivedita@alum.mit.edu>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
	Ard Biesheuvel <ardb@kernel.org>,
	linux-efi <linux-efi@vger.kernel.org>
Subject: Re: [PATCH 0/3] Relocate GOT before calling EFI stub
Date: Tue, 7 Jan 2020 13:32:24 -0500	[thread overview]
Message-ID: <20200107183224.GB1642410@rani.riverdale.lan> (raw)
In-Reply-To: <CAKv+Gu8Jsen-oAvUYrrTXnLRog+iHsLf0s6EMJ9smgUXpzncZw@mail.gmail.com>

On Tue, Jan 07, 2020 at 07:10:34PM +0100, Ard Biesheuvel wrote:
> On Tue, 7 Jan 2020 at 19:08, Arvind Sankar <nivedita@alum.mit.edu> wrote:
> >
> > On Tue, Jan 07, 2020 at 06:59:57PM +0100, Ard Biesheuvel wrote:
> > > On Tue, 7 Jan 2020 at 18:58, Arvind Sankar <nivedita@alum.mit.edu> wrote:
> > > >
> > > > On Tue, Jan 07, 2020 at 03:28:31PM +0100, Ard Biesheuvel wrote:
> > > > >
> > > > > Unfortunately, the command line option implements a weaker form of
> > > > > visibility than the pragma, so it probably comes down to setting the
> > > > > pragma in a .h file that gets -include'd via the command line so it is
> > > > > guaranteed to be seen first.
> > > >
> > > > Tried hacking that in and it works, tested with gcc 4.6.4.
> > >
> > > Excellent. But in my testing locally, I don't get any GOT entries in
> > > the first place, strangely enough. So what changes in the output for
> > > you with visibility hidden compared to before?
> >
> > Works with 32-bit as well.
> >
> > Are you checking libstub or boot/compressed? Below is with gcc 4.6 (but
> > latest binutils). With gcc 9, there's only one left -- trampoline_32bit_src
> > in pgtable_64.
> >
> 
> I am looking at the size of the .got section in
> boot/compressed/vmlinux, and it is 0x0 on 64-bit, and 0xc (i.e., only
> the .got.plt fixup code) on 32-bit.
> 
> Could you please check whether passing -Bsymbolic to the linker gives
> the same result btw?
> 

With new ld all those GOTPCRELX's get eliminated. If you add --no-relax
you'll get them in the .got. I don't have an old version of binutils so
I can't check, but I think they will be assembled as GOTPCREL and remain
in the .got section after linking.

A linker option can't help I'd think, because once these relocations are
there in the object files, you need the new binutils to get rid of them.
I didn't get any difference with -Bsymbolic -- also that seems to be for
shared libraries, with executables the references should already be
bound within the executable, shared libraries can't override them.

  reply	other threads:[~2020-01-07 18:32 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-07 13:54 [PATCH 0/3] Relocate GOT before calling EFI stub Arvind Sankar
2020-01-07 13:54 ` [PATCH 1/3] x86/boot/compressed/64: Make adjust_got easier to use repeatedly Arvind Sankar
2020-01-07 13:54 ` [PATCH 2/3] x86/boot/compressed/32: Allow adjust_got to be called repeatedly Arvind Sankar
2020-01-07 13:55 ` [PATCH 3/3] x86/boot: Perform GOT relocation before calling EFI stub Arvind Sankar
2020-01-07 14:01 ` [PATCH 0/3] Relocate GOT " Ard Biesheuvel
2020-01-07 14:13   ` Ard Biesheuvel
2020-01-07 14:21     ` Arvind Sankar
2020-01-07 14:24       ` Ard Biesheuvel
2020-01-07 14:27         ` Arvind Sankar
2020-01-07 14:28           ` Ard Biesheuvel
2020-01-07 17:58             ` Arvind Sankar
2020-01-07 17:59               ` Ard Biesheuvel
2020-01-07 18:08                 ` Arvind Sankar
2020-01-07 18:10                   ` Ard Biesheuvel
2020-01-07 18:32                     ` Arvind Sankar [this message]
2020-01-07 19:03                       ` Ard Biesheuvel
2020-01-07 19:14                         ` Arvind Sankar
2020-01-07 19:23                           ` Ard Biesheuvel
2020-01-07 19:51                             ` Ard Biesheuvel
2020-01-07 20:00                               ` Arvind Sankar

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