[Lldb-commits] [lldb] [lldb] Support DW_OP_WASM_location in DWARFExpression (PR #78977)

[Paolo Severini via lldb-commits]

https://github.com/paolosevMSFT created https://github.com/llvm/llvm-project/pull/78977

Add support for `DW_OP_WASM_location` in `DWARFExpression`.

>From 4bcf2b50123b18752108aad163a059577e360aa6 Mon Sep 17 00:00:00 2001
From: Paolo Severini <paolosev at microsoft.com>
Date: Mon, 22 Jan 2024 06:06:56 -0800
Subject: [PATCH] Add support for DW_OP_WASM_location to DWARFExpression

---
 lldb/source/Expression/DWARFExpression.cpp | 41 ++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/lldb/source/Expression/DWARFExpression.cpp b/lldb/source/Expression/DWARFExpression.cpp
index fe4928d4f43a434..95033db5ed8f5a1 100644
--- a/lldb/source/Expression/DWARFExpression.cpp
+++ b/lldb/source/Expression/DWARFExpression.cpp
@@ -346,6 +346,16 @@ static offset_t GetOpcodeDataSize(const DataExtractor &data,
     return (offset - data_offset) + subexpr_len;
   }
 
+  case DW_OP_WASM_location: {
+    uint8_t wasm_op = data.GetU8(&offset);
+    if (wasm_op == 3) {
+      data.GetU32(&offset);
+    } else {
+      data.GetULEB128(&offset);
+    }
+    return offset - data_offset;
+  }
+
   default:
     if (!dwarf_cu) {
       return LLDB_INVALID_OFFSET;
@@ -2595,6 +2605,37 @@ bool DWARFExpression::Evaluate(
       break;
     }
 
+    case DW_OP_WASM_location: {
+      uint8_t wasm_op = opcodes.GetU8(&offset);
+      uint32_t index;
+
+      /* LLDB doesn't have an address space to represents WebAssembly locals,
+       * globals and operand stacks.
+       * We encode these elements into virtual registers:
+       *   | tag: 2 bits | index: 30 bits |
+       *   where tag is:
+       *    0: Not a WebAssembly location
+       *    1: Local
+       *    2: Global
+       *    3: Operand stack value
+       */
+      if (wasm_op == 3) {
+        index = opcodes.GetU32(&offset);
+        wasm_op = 2; // Global
+      } else {
+        index = opcodes.GetULEB128(&offset);
+      }
+
+      reg_num = (((wasm_op + 1) & 0x03) << 30) | (index & 0x3fffffff);
+
+      if (ReadRegisterValueAsScalar(reg_ctx, reg_kind, reg_num, error_ptr, tmp))
+        stack.push_back(tmp);
+      else
+        return false;
+
+      break;
+    }
+
     default:
       if (dwarf_cu) {
         if (dwarf_cu->GetSymbolFileDWARF().ParseVendorDWARFOpcode(