Re: [PATCH 3/3] efi/libstub: arm64: set -fpie when building the EFI stub

[Matthias Kaehlcke <mka-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>]

El Thu, Jun 08, 2017 at 07:18:36PM +0000 Ard Biesheuvel ha dit:

> On 8 June 2017 at 19:08, Matthias Kaehlcke <mka-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> wrote:
> > El Thu, May 18, 2017 at 10:09:53AM +0100 Ard Biesheuvel ha dit:
> >
> >> Clang may emit absolute symbol references when building in non-PIC mode,
> >> even when using the default 'small' code model, which is already mostly
> >> position independent to begin with, due to its use of adrp/add pairs
> >> that have a relative range of +/- 4 GB. The remedy is to pass the -fpie
> >> flag, which can be done safely now that the code has been updated to avoid
> >> GOT indirections (which may be emitted due to the compiler assuming that
> >> the PIC/PIE code may end up in a shared library that is subject to ELF
> >> symbol preemption)
> >>
> >> Passing -fpie when building code that needs to execute at an a priori
> >> unknown offset is arguably an improvement in any case, and given that
> >> the recent visibility changes allow the PIC build to pass with GCC as
> >> well, let's add -fpie for all arm64 builds rather than only for Clang.
> >>
> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> >
> > Tested-by: Matthias Kaehlcke <mka-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
> 
> Thanks Matthias.
> 
> For the record, did you test only with Clang?

With both gcc and clang. Booting has only been tested with an older
kernel (v3.18), I suppose it shouldn't make a difference.