peter.smith added a comment. In D72959#1835368 <https://reviews.llvm.org/D72959#1835368>, @rjmccall wrote:
> There's two independently-useful things here for the relocation, right? > First, it's useful to be able to express a relocation to a symbol that has > the semantics of a particular function but doesn't necessarily have its > address, and that concept could be used across many "physical" relocations; > and second, it's potentially useful to have a shifted-by-two relative address > relocation, at least on AArch64 where instructions (and v-table entries under > this ABI) are always four-byte-aligned anyway. Is it possible to separate > these concerns in ELF, e.g. by having a "symbol" that can be the target of > any other relocation but which actually represents a function of unspecified > address with the semantics of another function? It would be possible to design relocations like that, but I think it would be difficult to fit into existing multi-target designs, which assume that the relocation code alone encodes all the actions a linker needs to take (smart-format, dumb-linker). My understanding of the reasons behind this are: - The linker can have millions of relocations to resolve and having all the actions explicit in the code simplifies its job. - There is a large space of available relocation codes, partitioned per target, but a much more limited availability of target specific symbol types and flags. - The concerns can be separated at implementation time, for example the symbol lookup, encoding and calculation stages are independent and shared between the codes. It is possible that there is a better trade-off in complexity, but anything radically different might need quite a bit of work to fit into an existing linker. Hope I've understood you correctly and apologies if the above isn't relevant. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D72959/new/ https://reviews.llvm.org/D72959 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
