[lld] [lld][WebAssembly] Fix use of undefined funcs under --warn-unresolved-symbols (PR #78643)

[Sam Clegg via llvm-commits]

https://github.com/sbc100 updated https://github.com/llvm/llvm-project/pull/78643

>From ee9f14650d3c6327b6c99b0dc2b6d5ed205e0a67 Mon Sep 17 00:00:00 2001
From: Sam Clegg <sbc at chromium.org>
Date: Thu, 18 Jan 2024 23:22:49 +0000
Subject: [PATCH] [lld][WebAssembly] Fix use of undefined funcs under
 --warn-unresolved-symbols

When undefined functions exist in the final link we need to create
stub functions (otherwise direct calls to those functions could
not be generated).  We were creating those stub when
`--unresolved-symbols=ignore-all` was passed but overlooked the fact
that `--warn-unresolved-symbols` essentially has the same effect (i.e.
undefined function can exist in the final link).

Fixes: #53987
---
 lld/test/wasm/unresolved-symbols.s | 17 +++++++++++------
 lld/wasm/Relocations.cpp           | 23 ++++++++++++-----------
 2 files changed, 23 insertions(+), 17 deletions(-)

diff --git a/lld/test/wasm/unresolved-symbols.s b/lld/test/wasm/unresolved-symbols.s
index 5de54d76c6de81..6e183e1878b3a7 100644
--- a/lld/test/wasm/unresolved-symbols.s
+++ b/lld/test/wasm/unresolved-symbols.s
@@ -18,10 +18,15 @@
 # RUN:   FileCheck -check-prefix=ERR1 %s
 
 ## Ignore all should not produce error and should not produce
-# any imports.  It should create a stub function in the place of the missing
-# function symbol.
+## any imports.  It should create a stub function in the place of the missing
+## function symbol.
 # RUN: wasm-ld %t1.o -o %t2.wasm --unresolved-symbols=ignore-all
 # RUN: obj2yaml %t2.wasm | FileCheck -check-prefix=IGNORE %s
+
+## --warn-unresolved-symbols should behave the same
+# RUN: wasm-ld %t1.o -o %t2.wasm --warn-unresolved-symbols
+# RUN: obj2yaml %t2.wasm | FileCheck -check-prefix=IGNORE %s
+
 # IGNORE-NOT: - Type:            IMPORT
 # IGNORE-NOT: - Type:            ELEM
 #
@@ -52,10 +57,10 @@
 # IGNORE-NEXT:      - Index:           3
 # IGNORE-NEXT:        Name:            get_func_addr
 
-## --import-undefined should handle unresolved funtions symbols
-# by importing them but still report errors/warning for missing data symbols.
-# `--allow-undefined` should behave like `--import-undefined` +
-# `--unresolve-symbols=ignore`
+## --import-undefined should handle unresolved functions symbols
+## by importing them but still report errors/warning for missing data symbols.
+## `--allow-undefined` should behave like `--import-undefined` +
+## `--unresolve-symbols=ignore`
 # RUN: wasm-ld %t1.o -o %t3.wasm --import-undefined --unresolved-symbols=ignore-all
 # RUN: obj2yaml %t3.wasm | FileCheck -check-prefix=IMPORT %s
 #      IMPORT:  - Type:            IMPORT
diff --git a/lld/wasm/Relocations.cpp b/lld/wasm/Relocations.cpp
index fcffacbc77af01..09b0a24ff011a9 100644
--- a/lld/wasm/Relocations.cpp
+++ b/lld/wasm/Relocations.cpp
@@ -54,21 +54,22 @@ static void reportUndefined(Symbol *sym) {
     case UnresolvedPolicy::Ignore:
       LLVM_DEBUG(dbgs() << "ignoring undefined symbol: " + toString(*sym) +
                                "\n");
-      if (!config->importUndefined) {
-        if (auto *f = dyn_cast<UndefinedFunction>(sym)) {
-          if (!f->stubFunction) {
-            f->stubFunction = symtab->createUndefinedStub(*f->getSignature());
-            f->stubFunction->markLive();
-            // Mark the function itself as a stub which prevents it from being
-            // assigned a table entry.
-            f->isStub = true;
-          }
-        }
-      }
       break;
     case UnresolvedPolicy::ImportDynamic:
       break;
     }
+
+    if (auto *f = dyn_cast<UndefinedFunction>(sym)) {
+      if (!f->stubFunction &&
+          config->unresolvedSymbols != UnresolvedPolicy::ImportDynamic &&
+          !config->importUndefined) {
+        f->stubFunction = symtab->createUndefinedStub(*f->getSignature());
+        f->stubFunction->markLive();
+        // Mark the function itself as a stub which prevents it from being
+        // assigned a table entry.
+        f->isStub = true;
+      }
+    }
   }
 }