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OvmfPkg: disable build-time relocation for DXEFV modules
When the GenFv utility from BaseTools composes a firmware volume, it checks whether modules in the firmware volume are subject to build-time relocation. The primary indication for relocation is whether the firmware volume has a nonzero base address, according to the [FD] section(s) in the FDF file that refer to the firmware volume. The idea behind build-time relocation is that XIP (execute in place) modules will not be relocated at boot-time: - Pre-DXE phase modules generally execute in place. (OVMF is no exception, despite the fact that we have writeable memory even in SEC: PEI_CORE and PEIMs run in-place from PEIFV, after SEC decompresses PEIFV and DXEFV from FVMAIN_COMPACT (flash) to RAM. PEI_CORE and the PEIMs are relocated at boot-time only after PlatformPei installs the permanent PEI RAM, and the RAM migration occurs.) - Modules dispatched by the DXE Core are generally relocated at boot-time. However, this is not necessarily so. Quoting Liming from <https://lists.01.org/pipermail/edk2-devel/2017-July/012053.html>: > PI spec has no limitation that XIP is for PEIM only. DXE driver may be > built as XIP for other purpose. For example, if DXE driver image address > is not zero, DxeCore will try allocating the preferred address and load > it. In another case, once DXE driver is relocated at build time, DxeCore > will dispatch it and start it directly without loading, it may save boot > performance. Therefore GenFv relocates even DXE and UEFI driver modules if the containing firmware volume has a nonzero base address. In OVMF, this is the case for both PEIV and DXEFV: > [FD.MEMFD] > BaseAddress = $(MEMFD_BASE_ADDRESS) > Size = 0xB00000 > ErasePolarity = 1 > BlockSize = 0x10000 > NumBlocks = 0xB0 > ... > 0x020000|0x0E0000 > gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfPeiMemFvSize > FV = PEIFV > > 0x100000|0xA00000 > gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDxeMemFvBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfDxeMemFvSize > FV = DXEFV While the build-time relocation certainly makes sense for PEIFV (see above), the reasons for which we specify DXEFV under [FD.MEMFD] are weaker: - we set the PcdOvmfDxeMemFvBase and PcdOvmfDxeMemFvSize PCDs here, - and we ascertain that DXEFV, when decompressed by SEC from FVMAIN_COMPACT, will fit into the area allotted here, at build time. In other words, the build-time relocation of the modules in DXEFV is a waste of resources. But, it gets worse: Build-time relocation of an executable is only possible if the on-disk and in-memory layouts are identical, i.e., if the sections of the PE/COFF image adhere to the same alignment on disk and in memory. Put differently, the FileAlignment and SectionAlignment headers must be equal. For boot-time modules that we build as part of edk2, both alignment values are 0x20 bytes. For runtime modules that we build as part of edk2, both alignment values are 0x1000 bytes. This is why the DXEFV relocation, albeit wasteful, is also successful every time. Unfortunately, if we try to include a PE/COFF binary in DXEFV that originates from outside of edk2, the DXEFV relocation can fail due to the binary having unmatched FileAlignment and SectionAlignment headers. This is precisely the case with the E3522X2.EFI network driver for the e1000 NIC, from Intel's BootUtil / PREBOOT.EXE distribution. The solution is to use the FvForceRebase=FALSE override under [FV.DXEFV]. This tells GenFv not to perform build-time relocation on the firmware volume, despite the FV having a nonzero base address. In DXEFV we also have SMM drivers. Those are relocated at boot-time (into SMRAM) unconditionally; SMRAM is always discovered at boot-time. Kudos to Ard and Liming for the PE/COFF sections & relocations explanation, and for the FvForceRebase=FALSE tip. I regression-tested this change in the following configurations (all with normal boot and S3 suspend/resume): IA32, q35, SMM, Linux IA32X64, q35, SMM, Linux IA32X64, q35, SMM, Windows-8.1 X64, i440fx, no-SMM, Linux Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Jordan Justen <jordan.l.justen@intel.com> Cc: Liming Gao <liming.gao@intel.com> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=613 Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=615 Suggested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Suggested-by: Liming Gao <liming.gao@intel.com> Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Laszlo Ersek <lersek@redhat.com> Reviewed-by: Liming Gao <liming.gao@intel.com> Acked-by: Jordan Justen <jordan.l.justen@intel.com>
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