Re: [PATCH 0/4] ArmVirtPkg: use PE/COFF metadata for self relocation

["Yao, Jiewen" <jiewen.yao@intel.com>]

Thank you Ard.
Good catch on jump-table stuff.

Acked-by: Jiewen Yao <Jiewen.yao@intel.com>

> -----Original Message-----
> From: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Sent: Tuesday, June 9, 2020 1:34 AM
> To: devel@edk2.groups.io
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>; Feng, Bob C
> <bob.c.feng@intel.com>; Gao, Liming <liming.gao@intel.com>; Laszlo Ersek
> <lersek@redhat.com>; Leif Lindholm <leif@nuviainc.com>; Ilias Apalodimas
> <ilias.apalodimas@linaro.org>; Julien Grall <julien@xen.org>; Yao, Jiewen
> <jiewen.yao@intel.com>
> Subject: [PATCH 0/4] ArmVirtPkg: use PE/COFF metadata for self relocation
> 
> 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@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> 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>
> 
> 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