[sysvabi64] Code Models. Limit range to GOT to 2GiB #345
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The R_AARCH64_GOTPCREL32 relocation, currently used in clang when relative vtables are enabled, has a signed offset so is limited to 2 GiB range. This limits the range of GOT from the vtables to 2GiB. Document this restriction in the tables for the small and medium code model. Add a note to explain the reason, so that if code generation does not use the relocation the distance to the GOT can be increased. Fixes ARM-software#343
Wilco1
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Aug 15, 2025
sysvabi64/sysvabi64.rst
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| 6. The distance to the GOT in the small and medium code model is | ||
| limited to 2GiB by the R_AARCH64_GOTPCREL32 relocations. |
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Basically in all cases (including large model) the max distance from text to GOT is 2GB if R_AARCH64_GOTPCREL32 is used. It is 4GB otherwise as the basic range of ADRP.
So I think it doesn't really need to be added to the table since there is no difference between the code models.
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Main reason I did that was the large code model (need to expand the text of the diff to see) says
| large | 2GiB | no restriction | max distance from text |
| | | | to GOT < 4 GiB |
If I take the table entries out, I'll need to take that out too. Will update the PR.
As all code-models have the same restriction. Only use the note to describe the 2GiB limit.
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Thank you! Taking out the table entries also addresses #288, right? |
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Yes, it looks like it does. I'll leave a comment and will close #288 |
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The R_AARCH64_GOTPCREL32 relocation, currently used in clang when relative vtables are enabled, has a signed offset so is limited to 2 GiB range. This limits the range of GOT from the vtables to 2GiB.
Document this restriction in the tables for the small and medium code model. Add a note to explain the reason, so that if code generation does not use the relocation the distance to the GOT can be increased.
Fixes #343