linux-kernel - Re: [PATCH 2/2] ARM: Wrap '--pic-veneer' with ld-option

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Message-ID: <20181205080645.GA11936@flashbox>
Date:   Wed, 5 Dec 2018 01:06:45 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Russell King <linux@...linux.org.uk>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Stefan Agner <stefan@...er.ch>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH 2/2] ARM: Wrap '--pic-veneer' with ld-option

On Wed, Dec 05, 2018 at 08:37:05AM +0100, Ard Biesheuvel wrote:
> On Wed, 5 Dec 2018 at 02:42, Nathan Chancellor <natechancellor@...il.com> wrote:
> >
> > This flag is not supported by lld:
> >
> >     ld.lld: error: unknown argument: --pic-veneer
> >
> > Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> 
> Hi Nate,
> 
> Does this mean ld.lld is guaranteed to produce position independent
> veneers if you build kernels that are bigger than the typical range of
> a relative branch?
> 

Hi Ard,

Honestly, I'm not quite sure. I saw your commit that introduced this
flag and I wasn't quite sure what to make of it for lld. What
configuration would I use to verify and what would I check for?

Additionally, I have filed an LLVM bug for the lld developers to
check and see if this is a flag they should support:

https://bugs.llvm.org/show_bug.cgi?id=39886

Thanks for the quick reply,
Nathan

> > ---
> >  arch/arm/Makefile | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> > index e2a0baf36766..4fab2aa29570 100644
> > --- a/arch/arm/Makefile
> > +++ b/arch/arm/Makefile
> > @@ -10,7 +10,7 @@
> >  #
> >  # Copyright (C) 1995-2001 by Russell King
> >
> > -LDFLAGS_vmlinux        := --no-undefined -X --pic-veneer
> > +LDFLAGS_vmlinux        := --no-undefined -X $(call ld-option,--pic-veneer)
> >  ifeq ($(CONFIG_CPU_ENDIAN_BE8),y)
> >  LDFLAGS_vmlinux        += --be8
> >  KBUILD_LDFLAGS_MODULE  += --be8
> > --
> > 2.20.0.rc1
> >