[llvm] [llvm-debuginfo-analyzer] Add support for WebAssembly binary format. (PR #82588)

[Carlos Alberto Enciso via llvm-commits]

================
@@ -429,10 +431,14 @@ void LVELFReader::processOneAttribute(const DWARFDie &Die, LVOffset *OffsetPtr,
         CurrentHighPC = *Address;
       if (std::optional<uint64_t> Offset = FormValue.getAsUnsignedConstant())
         // High PC is an offset from LowPC.
-        CurrentHighPC = CurrentLowPC + *Offset;
+        // Don't add the WebAssembly offset if we have seen a DW_AT_low_pc.
+        CurrentHighPC =
+            (FoundLowPC ? CurrentLowPC - WasmOffset : CurrentLowPC) + *Offset;
----------------
CarlosAlbertoEnciso wrote:

Your analysis is correct until the line where `CurrentHighPC` is calculated based on `CurrentLowPC`.
Referring again to the code for `DW_AT_high_pc`:
```
  case dwarf::DW_AT_high_pc:
        ...
      if (std::optional<uint64_t> Offset = FormValue.getAsUnsignedConstant())
        // Don't add the WebAssembly offset if we have seen a DW_AT_low_pc.
        CurrentHighPC =
            (FoundLowPC ? CurrentLowPC - WasmOffset : CurrentLowPC) + *Offset;
```
At this point:
`CurrentHighPC` is 140 - 100 + 10 = **50**, whereas `CurrentLowPC` is **140**
```
        ...
      // Consider the case of WebAssembly.
      CurrentHighPC += WasmOffset;
```
At this point:
`CurrentHighPC` will be 50 + 100 = **150**, whereas `CurrentLowPC` is **140** and their offset is **10** (with WasmOffset)
```
        ...
    break;
```
I hope this clarify as how the values are calculated.

https://github.com/llvm/llvm-project/pull/82588