[PATCH] D79664: [ELF] Support --pack-dyn-relocs=rel+relr

[Roland McGrath via Phabricator via llvm-commits]

mcgrathr added a comment.

Oh, and perhaps I'll update that comment since we do know why ELF specified RELA in the first place, which is for general-case reloc types for machines not like x86, where some reloc types don't apply to locations that store as many bits as the full address size that the addend can be in the general case.  When you have TEXTRELs, then any dynamic reloc can also be such a type.  For newer ABIs that never allowed TEXTRELs, I think people just assumed that the encoding for dynamic relocs should match the encoding for ET_REL relocs without thinking about it deeply.  In the ABIs we're concerned with today, the only narrow reloc type that might appear as a dynamic reloc is ABS32 in ELFCLASS64, but limiting addends to 32 bits is no more limiting than the rules of the small memory model, so you just wouldn't use rela->rel encoding with large memory model (or you could punt only for specific programs when you hit an out of range addend for real, which seems unlikely).  (A similar constraint has always been tolerated for R_ARM_MOV[WT]* relocs where EM_ARM is canonically REL rather than RELA and so addends used in relocs for movw/movt instructions are limited to 16 bits though the address computation is always a full 32 bit computation before the reloc stores the high or low 16 bits.)


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https://reviews.llvm.org/D79664