[edk2-devel] [PATCH 0/4] ArmVirtPkg: use PE/COFF metadata for self relocation

[Ard Biesheuvel]

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

Cc: Bob Feng <bob.c.feng at intel.com>
Cc: Liming Gao <liming.gao at intel.com>
Cc: Laszlo Ersek <lersek at redhat.com>
Cc: Leif Lindholm <leif at nuviainc.com>
Cc: Ilias Apalodimas <ilias.apalodimas at linaro.org>
Cc: Julien Grall <julien at xen.org>
Cc: Jiewen Yao <jiewen.yao at intel.com>

Ard Biesheuvel (4):
  ArmVirtPkg: add FDF rule for self-relocating PrePi
  BaseTools/Scripts/GccBase.lds: export image base symbol
  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                            | 21 +++++++++
 ArmVirtPkg/ArmVirtRules.fdf.inc                     |  5 ++
 ArmVirtPkg/PrePi/AArch64/ModuleEntryPoint.S         | 49 +++++---------------
 ArmVirtPkg/PrePi/Arm/ModuleEntryPoint.S             | 47 +++++--------------
 ArmVirtPkg/PrePi/Scripts/PrePi-PIE.lds              | 41 ----------------
 BaseTools/Scripts/GccBase.lds                       |  2 +
 12 files changed, 63 insertions(+), 152 deletions(-)
 delete mode 100644 ArmVirtPkg/Include/Platform/Hidden.h
 delete mode 100644 ArmVirtPkg/PrePi/Scripts/PrePi-PIE.lds

-- 
2.26.2


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