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add DWARF Wasm locations #43

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add DWARF Wasm locations #43

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18 changes: 13 additions & 5 deletions parser/src/file/dwarf.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3680,11 +3680,14 @@ where
// Skip and Call could be implemented if needed.
return Ok(pieces);
}
gimli::Operation::WasmLocal { .. }
| gimli::Operation::WasmGlobal { .. }
| gimli::Operation::WasmStack { .. } => {
// Unimplemented.
location = Some((Location::Other, false));
gimli::Operation::WasmLocal { index } => {
location = Some((Location::WasmLocal { index }, false));
}
gimli::Operation::WasmGlobal { index } => {
location = Some((Location::WasmGlobal { index }, false));
}
gimli::Operation::WasmStack { index } => {
location = Some((Location::WasmStack { index }, false));
}
}
if let Some((location, is_value)) = location {
Expand All @@ -3707,6 +3710,11 @@ where
Size::new(size_in_bits),
);
}
// https://docs.rs/gimli/latest/gimli/read/enum.Operation.html#variant.StackValue
// Commonly used for Wasm to terminate the expression.
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I must admit I'm not familiar enough with DWARF and not sure about that.
My understanding is that Wasm emits something like this: DW_OP_WASM_location ..., DW_OP_stack_value. Where DW_OP_stack_value is used to terminate the expression. Does this make sense?

I'm curious why this seems to be specific to Wasm.

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It appears to me that this is because DW_OP_WASM_location is only an address for the case for where wasm-op is wasm-local-indirect. For the other wasm-op values, the semantics are that it pushes the value of the local/global/operand onto the DWARF stack, so the result of the expression must be an implicit stack value rather than a location description. In my view this is a strange design, but I don't have much to do with Wasm so I don't know the reasons.

So rather than adding a case for Operation::StackValue here, what you need to do is change the gimli::Operation::Wasm* support to push a value onto the stack instead of setting location.

Also, it looks like gimli needs to be updated to add gimli::Operation::WasmLocalIndirect. I'm happy for that to be done later though if you don't need it yet.

gimli::Operation::StackValue => {
add_piece(&mut pieces, location, 0, is_value, Size::none());
}
_ => {
return Err(gimli::Error::InvalidPiece.into());
}
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15 changes: 15 additions & 0 deletions parser/src/location.rs
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Expand Up @@ -81,6 +81,21 @@ pub enum Location {
/// The offset.
offset: u64,
},
/// The value is stored in a Wasm local
WasmLocal {
/// The index of the local
index: u32,
},
/// The value is stored in a Wasm global
WasmGlobal {
/// The index of the global
index: u32,
},
/// The value is stored on the Wasm stack
WasmStack {
/// The index in the stack
index: u32,
},
/// The value is more complex than any of the above variants.
Other,
}
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