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[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
This commit is contained in:
Sam Clegg 2022-05-27 08:34:31 -07:00
parent 4f12a721f1
commit 0e8f4ce31d
2 changed files with 12 additions and 1 deletions
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11
lld/test/wasm/lto/weak-undefined.ll
View File

@ -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()

2
lld/wasm/SymbolTable.cpp
View File

@ -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 {