[lld] [LLD][COFF] Don't resolve weak aliases when performing local import (PR #152000)

[Jacek Caban via llvm-commits]

https://github.com/cjacek created https://github.com/llvm/llvm-project/pull/152000

Fixes crashes reported in #151255.

The alias may have already been stored for later resolution, which can lead to treating a resolved alias as if it were still undefined. Instead, use the alias target directly for the import.

Also extended the test to make reproducing the problem more likely, and added an assert that catches the issue.

>From c8080204000286e330506062c370fe50a274a35c Mon Sep 17 00:00:00 2001
From: Jacek Caban <jacek at codeweavers.com>
Date: Mon, 4 Aug 2025 18:28:27 +0200
Subject: [PATCH] [LLD][COFF] Don't resolve weak aliases when performing local
 import

Fixes crashes reported in #151255.

The alias may have already been stored for later resolution, which can lead
to treating a resolved alias as if it were still undefined. Instead, use the
alias target directly for the import.

Also extended the test to make reproducing the problem more likely, and added
an assert that catches the issue.
---
 lld/COFF/Driver.cpp                  |  4 +++-
 lld/COFF/SymbolTable.cpp             | 17 +++++------------
 lld/test/COFF/import_weak_alias.test | 13 ++++++++++---
 3 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
index 7580b469e4f87e..ff616d0ce2bffa 100644
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -2714,8 +2714,10 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   }
 
   ctx.symtab.initializeSameAddressThunks();
-  for (auto alias : aliases)
+  for (auto alias : aliases) {
+    assert(alias->kind() == Symbol::UndefinedKind);
     alias->resolveWeakAlias();
+  }
 
   if (config->mingw) {
     // Make sure the crtend.o object is the last object file. This object
diff --git a/lld/COFF/SymbolTable.cpp b/lld/COFF/SymbolTable.cpp
index de04cdff6483d1..e11d2c6dac83ec 100644
--- a/lld/COFF/SymbolTable.cpp
+++ b/lld/COFF/SymbolTable.cpp
@@ -478,17 +478,11 @@ void SymbolTable::resolveRemainingUndefines(std::vector<Undefined *> &aliases) {
     if (name.starts_with("__imp_")) {
       auto findLocalSym = [&](StringRef n) {
         Symbol *sym = find(n);
-        if (auto undef = dyn_cast_or_null<Undefined>(sym)) {
-          // The unprefixed symbol might come later in symMap, so handle it now
-          // if needed.
-          if (!undef->resolveWeakAlias())
-            sym = nullptr;
-        }
-        return sym;
+        return sym ? sym->getDefined() : nullptr;
       };
 
       StringRef impName = name.substr(strlen("__imp_"));
-      Symbol *imp = findLocalSym(impName);
+      Defined *imp = findLocalSym(impName);
       if (!imp && isEC()) {
         // Try to use the mangled symbol on ARM64EC.
         std::optional<std::string> mangledName =
@@ -502,11 +496,10 @@ void SymbolTable::resolveRemainingUndefines(std::vector<Undefined *> &aliases) {
             imp = findLocalSym(*mangledName);
         }
       }
-      if (imp && isa<Defined>(imp)) {
-        auto *d = cast<Defined>(imp);
-        replaceSymbol<DefinedLocalImport>(sym, ctx, name, d);
+      if (imp) {
+        replaceSymbol<DefinedLocalImport>(sym, ctx, name, imp);
         localImportChunks.push_back(cast<DefinedLocalImport>(sym)->getChunk());
-        localImports[sym] = d;
+        localImports[sym] = imp;
         continue;
       }
     }
diff --git a/lld/test/COFF/import_weak_alias.test b/lld/test/COFF/import_weak_alias.test
index ae1817c67a20ac..ff07022741d1c8 100644
--- a/lld/test/COFF/import_weak_alias.test
+++ b/lld/test/COFF/import_weak_alias.test
@@ -4,17 +4,24 @@
 # RUN: llvm-mc --filetype=obj -triple=x86_64-windows-msvc %t.dir/foo.s -o %t.foo.obj
 # RUN: llvm-mc --filetype=obj -triple=x86_64-windows-msvc %t.dir/qux.s -o %t.qux.obj
 # RUN: lld-link %t.qux.obj %t.foo.obj -out:%t.dll -dll
+# RUN: lld-link %t.foo.obj %t.qux.obj -out:%t.dll -dll
 #
 #--- foo.s
 .text
 bar:
   ret
 
-.weak foo
-.set foo, bar
+.weak a
+.weak b
+.weak c
+.set a, bar
+.set b, bar
+.set c, bar
 #--- qux.s
 .text
 .global _DllMainCRTStartup
 _DllMainCRTStartup:
-  call *__imp_foo(%rip)
+  call *__imp_a(%rip)
+  call *__imp_b(%rip)
+  call *__imp_c(%rip)
   ret