[PATCH v2 0/3] ArmVirtPkg: use PE/COFF metadata for self relocation

["Ard Biesheuvel" <ard.biesheuvel@arm.com>]

As suggested by Jiewen in response to Ilias RFC [0], it is better to use
the PE/COFF metadata for self-relocating executables than to rely on ELF
metadata, given how the latter is only available when using ELF based
toolchains. Also, we have had some maintenance issues with this code in
the past, as PIE linking of non-position independent objects is not a well
tested code path in toolchains in general.

So implement this for the self-relocating PrePi in ArmVirtPkg first.

First, we need to ensure that the module in question is emitted with its
PE/COFF relocation metadata preserved, by creating a special FDF rule.

We also need to provide a way for the code to refer to the start of the
image directly, by adding it to the linker script.

Then, it is simply a matter of swapping out the two assembly routines,
and adding the C code that serves the same purpose but based on PE/COFF
base relocations.

Note that PE/COFF relocations are considerably more compact than ELF RELA
relocations, so this does not impact the memory footprint of the resulting
image adversely.

[0] https://edk2.groups.io/g/devel/message/60835

Changes since v1:
- Drop change to linker script, and instead, use the existing FV parsing code
  (which is already incorporated into PrePi to load other modules), to find
  the start address of the image before relocation. This way, we can support
  TE images as well as PE32 images naturally, and not rely on GCC/binutils
  specific artifacts that make porting to a native PE/COFF toolchain more
  difficult
- Switch to TE format in the SELF_RELOC FDF rule - this is not terribly
  likely to matter in practice, but since PrePi is the only module that
  is incorporated in uncompressed form, and given that we used TE format
  before these changes, it is a more appropriate default.
- Add acks from Jiewen, Laszlo and Sami. Note that I have dropped the
  Tested-bys - apologies for wasting anyone's time, but they could not
  be carried over due to the changes.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Julien Grall <julien@xen.org>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Sami Mujawar <Sami.Mujawar@arm.com>

Ard Biesheuvel (3):
  ArmVirtPkg: add FDF rule for self-relocating PrePi
  ArmVirtPkg/PrePi: use standard PeCoff routines for self-relocation
  ArmVirtPkg: remove unused files

 ArmVirtPkg/ArmVirtQemuKernel.dsc                    | 10 ++--
 ArmVirtPkg/ArmVirtXen.dsc                           | 10 ++--
 ArmVirtPkg/ArmVirtQemuKernel.fdf                    |  2 +-
 ArmVirtPkg/ArmVirtXen.fdf                           |  2 +-
 ArmVirtPkg/PrePi/ArmVirtPrePiUniCoreRelocatable.inf |  4 +-
 ArmVirtPkg/Include/Platform/Hidden.h                | 22 ---------
 ArmVirtPkg/PrePi/PrePi.c                            | 35 ++++++++++++++
 ArmVirtPkg/ArmVirtRules.fdf.inc                     |  5 ++
 ArmVirtPkg/PrePi/AArch64/ModuleEntryPoint.S         | 49 +++++---------------
 ArmVirtPkg/PrePi/Arm/ModuleEntryPoint.S             | 47 +++++--------------
 ArmVirtPkg/PrePi/Scripts/PrePi-PIE.lds              | 41 ----------------
 11 files changed, 75 insertions(+), 152 deletions(-)
 delete mode 100644 ArmVirtPkg/Include/Platform/Hidden.h
 delete mode 100644 ArmVirtPkg/PrePi/Scripts/PrePi-PIE.lds

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2.26.2