[PATCH] D43264: [WebAssembly] Add explicit symbol table

Rui Ueyama via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Thu Feb 15 18:08:11 PST 2018

ruiu added a comment.

> By that logic, you wouldn't need InputSection at if all in the ELF linker. You just put the body of each symbol on the symbols, rather than allowing multiple symbols to defence the same section.

I don't know if I understand what you wrote correctly. In ELF, you need both symbols and sections in the linker. One section can have multiple symbols at its various offsets, and some of them are aliases (e.g. two symbols can point to the same location in the same section).

> Globals are really more like data symbols. An int variable would have a 4-byte section asking the ELF interpreter to allocate 4 bytes of ram. A wasm global I32 has its own section in the wasm file, asking for a 4byte register-backed region to be allocated.

Well, that runtime allocates some memory at runtime doesn't necessarily mean that that has to be represented as Chunk. At least to me the use of Chunk in this patch to represent Globals is very odd and is not an intended use of Chunk. Chunk is designed to represent sections or something like that, and Globals is different.

> Do we have a different understanding of "imported"? An imported function is definitely undefined from a wasm and a linking point of view - both in ELF and warm, the function symbols with no body are undefined and the linker is looking for a definition against which to reduce any calls.

By imported, I mean symbols in DSO (DLL) files. In ELF, it's SharedSymbol. In COFF, It's DLLImported symbol. They are considered "defined" because they are already resolved, but the actual code is not given until load-time.

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