[PATCH] D91203: [WebAssembly] Fixed wasm64 DWARF using 64-bit code pointer sizes

[Wouter van Oortmerssen via Phabricator via llvm-commits]

aardappel added a comment.

@dblaikie Confusingly, these are all different: function pointers at runtime (in a Wasm VM) are 32-bit indices. LLVM function pointers are 64-bit in wasm64 for consistency, but get truncated when lowered in Isel. Then here we have a 3rd kind of code pointer, just for DWARF, since Wasm doesn't have the concept of a pointer to an instruction inside a function (which DWARF needs for DW_AT_low_pc, and we need to relocate).

And yes, if this is also used for globals, and there is an architecture for which code pointers would be smaller than global pointers, then this patch would break them.

An alternative solution for Wasm would be to just go along with the expected 64-bit size for DW_FORM_addr, but that would mean wasted space, and a new reloc type for us. Also means DWARF data between wasm32 and wasm64 is different.


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  https://reviews.llvm.org/D91203/new/

https://reviews.llvm.org/D91203