lkml.org 
[lkml]   [2018]   [Dec]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH 2/2] ARM: Wrap '--pic-veneer' with ld-option
On Wed, Dec 5, 2018 at 12:10 AM Ard Biesheuvel
<ard.biesheuvel@linaro.org> wrote:
>
> (+ Arnd)
>
> On Wed, 5 Dec 2018 at 09:06, Nathan Chancellor <natechancellor@gmail.com> wrote:
> >
> > On Wed, Dec 05, 2018 at 08:37:05AM +0100, Ard Biesheuvel wrote:
> > > On Wed, 5 Dec 2018 at 02:42, Nathan Chancellor <natechancellor@gmail.com> wrote:
> > > >
> > > > This flag is not supported by lld:
> > > >
> > > > ld.lld: error: unknown argument: --pic-veneer
> > > >
> > > > Signed-off-by: Nathan Chancellor <natechancellor@gmail.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?

(+ Peter) who might be able to answer this.

> > >
> >
> > 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?
> >
>
> Try building allyesconfig, and check the resulting binary for veneers
> (which have 'veneer' in the symbol name, at least when ld.bfd emits
> them). These veneers should not take the [virtual] address of the
> branch target directly, but take a PC relative offset (as in the
> example in the commit log of that patch you are referring to)

Not sure clang can compile an arm32 allyesconfig (haven't tried
personally, yet, TODO), but we could try gcc+lld.

>
> > 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
> > > >



--
Thanks,
~Nick Desaulniers

\
 
 \ /
  Last update: 2018-12-05 19:22    [W:0.094 / U:0.868 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site