Revert "Add GP-relative relocations" #427
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This reverts commit d49e480. Both the ePIC and FDPIC ABIs are expected to define relocation types which can be used for both PC-relative and GP-relative data, and are expected to define relaxations to optimize access to both types of data. Explicit, compiler-generated relocations using GP are only useful in cases where an object is known at compile time to be local and present in the GP-relative segment. The relaxations will result in GP-relative accesses, but the relocations involved will be linker internal and need not have allocated standard numbers.
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I have made extensive investigations of older solutions (-msep-data, -mid-shared-library, -mno-pic-data-is-text-relative, -fropi and -frwpi, -mfdpic; m68k/sh4/arm) and will keep adding notes to https://maskray.me/blog/2024-02-20-mmu-less-systems-and-fdpic
I agree that these GP-relative relocation types will not be useful.
With suitable optimizations and relaxations, the ePIC relocations can be completely replaced.
AFAIK, these relocation types haven't been used in any upstream projects.
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LGTM but I would like to merge this until #405 update :) cc. @luismarques |
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Sounds reasonable. |
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I am now working on ARM FDPIC for LLVM+Clang to get some engineering experience. Yes, I am more convinced we should remove relocation types for direct GP-relative addressing:) |
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Should I merge this, then? |
kito-cheng
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kito-cheng
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Let moving forward :)
This reverts commit d49e480.
Both the ePIC and FDPIC ABIs are expected to define relocation types which can be used for both PC-relative and GP-relative data, and are expected to define relaxations to optimize access to both types of data. Explicit, compiler-generated relocations using GP are only useful in cases where an object is known at compile time to be local and present in the GP-relative segment. The relaxations will result in GP-relative accesses, but the relocations involved will be linker internal and need not have allocated standard numbers.