Re: [edk2-devel] [RFT PATCH v2 1/6] BaseTools/tools_def XCODE: Link X64 with -read_only_relocs suppress

["Marvin Häuser" <mhaeuser@posteo.de>]

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Hi Ard,

Sorry, I cannot preserve the CC list as the groups.io interface doesn't seem to allow it. Can you please CC me on future revisions?

This patch will badly corrupt binaries. I cannot cite a source right now (if you want me to, please remind me in your response, so I can look it up tomorrow), but for X64 (but not IA32, which is why this is enabled there), relocs are relative to the first *writable* segment. In other words, any relocation to __TEXT will badly corrupt binaries this way.

In AUDK, we support this with two essential changes. The first is that we always generate a writable dummy segment at the beginning of the address space [1], making the relocs relative to the image base. The second is that in ocmtoc, our fork of the abandoned (and pretty badly-bugged) Apple mtoc, we explicitly require this segment to be present and verify its virtual address is the minimum virtual address [2]. It is then omitted from the conversion process [3]. I suggest you replicate these changes and fully switch to ocmtoc for XCODE5 builds.

Best regards,
Marvin

[1]
https://github.com/acidanthera/audk/blob/c382e9c571c7d5f39ba53b46a0c723c7943f33c5/BaseTools/Conf/tools_def.template#L2976-L2988

[2]
https://github.com/acidanthera/ocmtoc/blob/b0152c51beae264770c3faf0d213f9594ee043be/efitools/mtoc.c#L1097-L1123
https://github.com/acidanthera/ocmtoc/blob/b0152c51beae264770c3faf0d213f9594ee043be/efitools/mtoc.c#L1204-L1214

[3]
https://github.com/acidanthera/ocmtoc/blob/b0152c51beae264770c3faf0d213f9594ee043be/efitools/mtoc.c#L1307-L1311

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