From cccc61da54776d13fdb1655631e9ae3b81dd2ab3 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sat, 8 Mar 2025 14:46:09 +0000
Subject: Support undefined data elements in Wasm binary format

---
 .../wasm/structure/ast/modules/WasmModule.java     | 50 +++++++++++++++++-----
 .../structure/binary/WasmBinaryFormatLinking.java  | 24 +++++++++++
 2 files changed, 63 insertions(+), 11 deletions(-)

(limited to 'src/main/java')

diff --git a/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/modules/WasmModule.java b/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/modules/WasmModule.java
index 7fc9e9f9..67aef746 100644
--- a/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/modules/WasmModule.java
+++ b/src/main/java/org/shedlang/compiler/backends/wasm/structure/ast/modules/WasmModule.java
@@ -19,7 +19,8 @@ public record WasmModule(
     PVector<WasmDataSegment> dataSegments,
     PVector<WasmImport> imports,
     PVector<WasmInitFunc> initFuncs,
-    PVector<WasmTag> tags
+    PVector<WasmTag> tags,
+    PVector<String> undefinedDataElementNames
 ) {
     public static final WasmModule EMPTY = new WasmModule(
         P.orderedSet(),
@@ -31,6 +32,7 @@ public record WasmModule(
         P.vector(),
         P.vector(),
         P.vector(),
+        P.vector(),
         P.vector()
     );
 
@@ -170,7 +172,8 @@ public record WasmModule(
             dataSegments,
             imports,
             initFuncs,
-            tags
+            tags,
+            this.undefinedDataElementNames
         );
     }
 
@@ -185,7 +188,8 @@ public record WasmModule(
             dataSegments,
             imports,
             initFuncs,
-            tags
+            tags,
+            this.undefinedDataElementNames
         );
     }
 
@@ -200,7 +204,8 @@ public record WasmModule(
             dataSegments,
             imports,
             initFuncs,
-            tags
+            tags,
+            this.undefinedDataElementNames
         );
     }
 
@@ -215,7 +220,8 @@ public record WasmModule(
             dataSegments,
             imports,
             initFuncs,
-            tags
+            tags,
+            this.undefinedDataElementNames
         );
     }
 
@@ -230,7 +236,8 @@ public record WasmModule(
             dataSegments,
             imports,
             initFuncs,
-            tags
+            tags,
+            this.undefinedDataElementNames
         );
     }
 
@@ -245,7 +252,8 @@ public record WasmModule(
             dataSegments,
             imports,
             initFuncs,
-            tags
+            tags,
+            this.undefinedDataElementNames
         );
     }
 
@@ -260,7 +268,8 @@ public record WasmModule(
             dataSegments.plus(dataSegment),
             imports,
             initFuncs,
-            tags
+            tags,
+            this.undefinedDataElementNames
         );
     }
 
@@ -282,7 +291,8 @@ public record WasmModule(
             dataSegments,
             newImports,
             initFuncs,
-            tags
+            tags,
+            this.undefinedDataElementNames
         );
     }
 
@@ -297,7 +307,8 @@ public record WasmModule(
             dataSegments,
             imports,
             initFuncs.plus(initFunc),
-            tags
+            tags,
+            this.undefinedDataElementNames
         );
     }
 
@@ -312,7 +323,24 @@ public record WasmModule(
             dataSegments,
             imports,
             initFuncs,
-            tags.plus(tag)
+            tags.plus(tag),
+            this.undefinedDataElementNames
+        );
+    }
+
+    public WasmModule addUndefinedDataElement(String name) {
+        return new WasmModule(
+            types,
+            functions,
+            tables,
+            memories,
+            globals,
+            elementSegments,
+            dataSegments,
+            imports,
+            initFuncs,
+            tags,
+            this.undefinedDataElementNames.plus(name)
         );
     }
 }
diff --git a/src/main/java/org/shedlang/compiler/backends/wasm/structure/binary/WasmBinaryFormatLinking.java b/src/main/java/org/shedlang/compiler/backends/wasm/structure/binary/WasmBinaryFormatLinking.java
index 6b8ff4ca..d874dda8 100644
--- a/src/main/java/org/shedlang/compiler/backends/wasm/structure/binary/WasmBinaryFormatLinking.java
+++ b/src/main/java/org/shedlang/compiler/backends/wasm/structure/binary/WasmBinaryFormatLinking.java
@@ -209,6 +209,11 @@ public class WasmBinaryFormatLinking {
                 writer.writeUnsignedInt32(data.offset());
                 writer.writeUnsignedInt32(data.size());
             }
+            case SymbolInfo.DataUndefined dataUndefined -> {
+                writer.writeByte(SymbolType.DATA.id);
+                writeFlags(dataUndefined.flags, writer);
+                writer.writeString(dataUndefined.name());
+            }
             case SymbolInfo.Global global -> {
                 writer.writeByte(SymbolType.GLOBAL.id);
                 writeFlags(global.flags, writer);
@@ -442,6 +447,19 @@ public class WasmBinaryFormatLinking {
             tableNameToSymbolIndex.put(table.name(), symbolIndex);
         }
 
+        for (var undefinedDataElementName : module.undefinedDataElementNames()) {
+            var symbolInfo = new SymbolInfo.DataUndefined(
+                List.of(SymbolFlag.UNDEFINED),
+                undefinedDataElementName
+            );
+            var symbolIndex = new WasmSymbolIndex(symbolInfos.size());
+            symbolInfos.add(symbolInfo);
+            memoryAddressToSymbolIndex.put(
+                new WasmMemoryAddress(undefinedDataElementName),
+                symbolIndex
+            );
+        }
+
         return new SymbolTable(
             symbolInfos,
             memoryAddressToSymbolIndex,
@@ -466,6 +484,12 @@ public class WasmBinaryFormatLinking {
         ) implements SymbolInfo {
         }
 
+        record DataUndefined(
+            List<SymbolFlag> flags,
+            String name
+        ) implements SymbolInfo {
+        }
+
         record Global(List<SymbolFlag> flags, WasmGlobalIndex globalIndex, String name) implements SymbolInfo {
         }
 
-- 
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