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 <ler...@redhat.com> Cc: Leif Lindholm <l...@nuviainc.com> Cc: Ilias Apalodimas <ilias.apalodi...@linaro.org> Cc: Julien Grall <jul...@xen.org> Cc: Jiewen Yao <jiewen....@intel.com> Cc: Sami Mujawar <sami.muja...@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 -- 2.26.2 -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#61140): https://edk2.groups.io/g/devel/message/61140 Mute This Topic: https://groups.io/mt/74817463/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
