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

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

On 8 June 2017 at 19:08, Matthias Kaehlcke [off-list ref] wrote:

quoted

El Thu, May 18, 2017 at 10:09:53AM +0100 Ard Biesheuvel ha dit:

quoted

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 <redacted>

Tested-by: Matthias Kaehlcke <mka@chromium.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.