[WebAssembly][Object]Use file offset as function symbol address for linked files (#76198)

WebAssembly doesn't have a single virtual memory space the way other
object formats or architectures do, so "addresses" mean different things
depending on the context.
Function symbol addresses in object files are offsets from the start of
the code section. This is good for linking and relocation. However when
dealing with linked binaries, offsets from the start of the file/module
are more often used (e.g. for stack traces in browsers), and are more
useful for use cases like binary size attribution. This PR changes
Object to use the file offset instead of the section offset for function
symbols, but only for linked (non-DSO) files.

This implements item number 4 from #76107

1 files changed, 12 insertions, 4 deletions

diff --git a/llvm/lib/Object/WasmObjectFile.cpp b/llvm/lib/Object/WasmObjectFile.cpp
index 40665d6..ccc29d0 100644
--- a/llvm/lib/Object/WasmObjectFile.cpp
+++ b/llvm/lib/Object/WasmObjectFile.cpp
@@ -1667,10 +1667,18 @@ Expected<StringRef> WasmObjectFile::getSymbolName(DataRefImpl Symb) const {
 Expected<uint64_t> WasmObjectFile::getSymbolAddress(DataRefImpl Symb) const {
   auto &Sym = getWasmSymbol(Symb);
   if (Sym.Info.Kind == wasm::WASM_SYMBOL_TYPE_FUNCTION &&
-      isDefinedFunctionIndex(Sym.Info.ElementIndex))
-    return getDefinedFunction(Sym.Info.ElementIndex).CodeSectionOffset;
-  else
-    return getSymbolValue(Symb);
+      isDefinedFunctionIndex(Sym.Info.ElementIndex)) {
+    // For object files, use the section offset. The linker relies on this.
+    // For linked files, use the file offset. This behavior matches the way
+    // browsers print stack traces and is useful for binary size analysis.
+    // (see https://webassembly.github.io/spec/web-api/index.html#conventions)
+    uint32_t Adjustment = isRelocatableObject() || isSharedObject()
+                              ? 0
+                              : Sections[CodeSection].Offset;
+    return getDefinedFunction(Sym.Info.ElementIndex).CodeSectionOffset +
+           Adjustment;
+  }
+  return getSymbolValue(Symb);
 }
 
 uint64_t WasmObjectFile::getWasmSymbolValue(const WasmSymbol &Sym) const {