[lld][WebAssembly] Fix crash on undefined+weak function syms in LTO objects

Symbols from LTO objects don't contain Wasm signatures, but we need a
signature when we create undefined/stub functions for missing weakly
undefined symbols.

Luckily, after LTO, we know that symbols that are not referenced by a
regular object file must not be needed in the final output so there
is no need to generate undefined/stub function for them.

Differential Revision: https://reviews.llvm.org/D126554

diff --git a/lld/test/wasm/lto/weak-undefined.ll b/lld/test/wasm/lto/weak-undefined.ll
index 36e4228..9a42c2b 100644 (file)
--- a/lld/test/wasm/lto/weak-undefined.ll
+++ b/lld/test/wasm/lto/weak-undefined.ll
@@ -11,6 +11,17 @@ target triple = "wasm32-unknown-unknown"
 
 declare extern_weak i32 @foo()
 
+declare extern_weak i32 @bar()
+
+; The reference to bar here will exist in the LTO file, but the LTO process will
+; remove it, so it will never be referenced by an normal object file, and
+; therefore never have a signature.
+define void @unused_function() #0 {
+entry:
+    %call2 = call i32 @bar()
+    ret void
+}
+
 define void @_start() #0 {
 entry:
     %call2 = call i32 @foo()

diff --git a/lld/wasm/SymbolTable.cpp b/lld/wasm/SymbolTable.cpp
index ef14022..2969d99 100644 (file)
--- a/lld/wasm/SymbolTable.cpp
+++ b/lld/wasm/SymbolTable.cpp
@@ -854,7 +854,7 @@ void SymbolTable::replaceWithUndefined(Symbol *sym) {
 // the call instruction that passes Wasm validation.
 void SymbolTable::handleWeakUndefines() {
   for (Symbol *sym : getSymbols()) {
-    if (sym->isUndefWeak()) {
+    if (sym->isUndefWeak() && sym->isUsedInRegularObj) {
       if (sym->getSignature()) {
         replaceWithUndefined(sym);
       } else {