[lld][WebAssebmly] Preserve custom import attributes with LTO
Undefined symbols in WebAssembly can come with custom `import-module`
and `import-field` attributes. However when reading symbols from
bitcode object files during LTO those curtom attributes are not
available.
Once we compile the LTO object and read in the symbol table from the
object file we have access to these custom attributes. In this case,
when undefined symbols are added and a symbol already exists in the
SymbolTable we can't simple return it, we may need to update the
symbol's attributes.
Fixes: PR43211
Differential Revision: https://reviews.llvm.org/D68959
llvm-svn: 375081
diff --git a/lld/wasm/SymbolTable.cpp b/lld/wasm/SymbolTable.cpp
index 92069ea..14616f9 100644
--- a/lld/wasm/SymbolTable.cpp
+++ b/lld/wasm/SymbolTable.cpp
@@ -393,6 +393,36 @@
return s;
}
+// This function get called when an undefined symbol is added, and there is
+// already an existing one in the symbols table. In this case we check that
+// custom 'import-module' and 'import-field' symbol attributes agree.
+// With LTO these attributes are not avialable when the bitcode is read and only
+// become available when the LTO object is read. In this case we silently
+// replace the empty attributes with the valid ones.
+template <typename T>
+static void setImportAttributes(T *existing, StringRef importName,
+ StringRef importModule, InputFile *file) {
+ if (!importName.empty()) {
+ if (existing->importName.empty())
+ existing->importName = importName;
+ if (existing->importName != importName)
+ error("import name mismatch for symbol: " + toString(*existing) +
+ "\n>>> defined as " + existing->importName + " in " +
+ toString(existing->getFile()) + "\n>>> defined as " + importName +
+ " in " + toString(file));
+ }
+
+ if (!importModule.empty()) {
+ if (existing->importModule.empty())
+ existing->importModule = importModule;
+ if (existing->importModule != importModule)
+ error("import module mismatch for symbol: " + toString(*existing) +
+ "\n>>> defined as " + existing->importModule + " in " +
+ toString(existing->getFile()) + "\n>>> defined as " + importModule +
+ " in " + toString(file));
+ }
+}
+
Symbol *SymbolTable::addUndefinedFunction(StringRef name, StringRef importName,
StringRef importModule,
uint32_t flags, InputFile *file,
@@ -424,10 +454,10 @@
reportTypeError(s, file, WASM_SYMBOL_TYPE_FUNCTION);
return s;
}
+ auto *existingUndefined = dyn_cast<UndefinedFunction>(existingFunction);
if (!existingFunction->signature && sig)
existingFunction->signature = sig;
if (isCalledDirectly && !signatureMatches(existingFunction, sig)) {
- auto* existingUndefined = dyn_cast<UndefinedFunction>(existingFunction);
// If the existing undefined functions is not called direcltly then let
// this one take precedence. Otherwise the existing function is either
// direclty called or defined, in which case we need a function variant.
@@ -436,6 +466,8 @@
else if (getFunctionVariant(s, sig, file, &s))
replaceSym();
}
+ if (existingUndefined)
+ setImportAttributes(existingUndefined, importName, importModule, file);
}
return s;