DW_OP_WASM_location is unsupported

[RReverser]

When trying to dwarfdump any Wasm file produced with latest Clang or Rust, DW_AT_frame_base looks like this:

DW_AT_frame_base            len 0x0007: ed03000000009f: WARNING: unsupported operation 0xed

Looks like Gimli needs to be taught DW_OP_WASM_location as described at https://yurydelendik.github.io/webassembly-dwarf/#DWARF-expressions-and-location-descriptions. /cc @yurydelendik

[yurydelendik]

Yes, it will be nice to have Wasm DWARF support. At least under the feature. We are using crude hack in the wasmtime project.

[philipc]

Are the semantics of this operation similar to DW_OP_regx (rather than DW_OP_bregx)?

[RReverser]

@philipc I guess depends what you mean by semantics... The attached link likely explains it better than I could.

[philipc]

Does it complete the expression or piece (as in DW_OP_regx), or does it push a value on the stack (as in DW_OP_bregx)? I assume it is the former. Would Wasm ever have a need for the later?

[RReverser]

AFAIK it's the former, yes.

[philipc]

So having implemented this in #546, I see that llvm is emitting a DW_OP_stack_value after it, which I think would only make sense if it pushed a value on the stack. @yurydelendik Can you take a look at this please?

[RReverser]

So having implemented this in #546, I see that llvm is emitting a DW_OP_stack_value after it, which I think would only make sense if it pushed a value on the stack. @yurydelendik Can you take a look at this please?

Note that this is being fixed in https://reviews.llvm.org/D94347/new/, which also adds support for indirect values (0x02).

So DW_OP_WASM_location will be completing the expression.