[lld] [lld][WebAssembly] Fix regression in function signature checking (PR #78831)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-lld-wasm

Author: Sam Clegg (sbc100)

<details>
<summary>Changes</summary>

Followup to #<!-- -->78658, which caused a regression in emscripten.

When a lazy symbol is added, which resolved and existing undefined symbol, we don't need/want to replace the undefined symbol with the lazy one.  Instead we called extract, which replaces the undefined symbol with the defined one.

The fact that we were first replacing the undefined symbol with a lazy one before extracting the archive member doesn't normally matter but, in the case of the function symbol, replacing the undefined symbol with a lazy symbol means that `addDefinedFunction` sees the existing symbol as lazy and simply replaces it.

Note that this is consistent with both the ELF code in `Symbol::resolve(const LazySymbol &other)` and the wasm code prior to
 #<!-- -->78658, neither of which replace the existing symbol with the lazy one
in this case.

---
Full diff: https://github.com/llvm/llvm-project/pull/78831.diff


3 Files Affected:

- (modified) lld/test/wasm/signature-mismatch.s (+10-1) 
- (modified) lld/wasm/SymbolTable.cpp (+3-3) 
- (modified) lld/wasm/Symbols.h (+1-1) 


``````````diff
diff --git a/lld/test/wasm/signature-mismatch.s b/lld/test/wasm/signature-mismatch.s
index 5d305efca246496..7dc1b8ced3530d5 100644
--- a/lld/test/wasm/signature-mismatch.s
+++ b/lld/test/wasm/signature-mismatch.s
@@ -8,6 +8,11 @@
 # RUN: wasm-ld -r -o %t.reloc.o %t.main.o %t.ret32.o %t.call.o 2>&1 | FileCheck %s -check-prefix=WARN
 # RUN: obj2yaml %t.reloc.o | FileCheck %s -check-prefix=RELOC
 
+# RUN: rm -f %t.a
+# RUN: ar crS %t.a %t.ret32.o %t.call.o
+# RUN: wasm-ld --export=call_ret32 --export=ret32 -o %t2.wasm %t.main.o %t.a 2>&1 | FileCheck %s -check-prefix=ARCHIVE
+# RUN: obj2yaml %t2.wasm | FileCheck %s -check-prefix=YAML
+
 # RUN: not wasm-ld --fatal-warnings -o %t.wasm %t.main.o %t.ret32.o %t.call.o 2>&1 | FileCheck %s -check-prefix=ERROR
 
 .functype ret32 (i32, i64, i32) -> (i32)
@@ -42,6 +47,10 @@ ret32_address_main:
 # WARN-NEXT: >>> defined as (i32, i64, i32) -> i32 in {{.*}}.main.o
 # WARN-NEXT: >>> defined as (f32) -> i32 in {{.*}}.ret32.o
 
+# ARCHIVE: warning: function signature mismatch: ret32
+# ARCHIVE-NEXT: >>> defined as (i32, i64, i32) -> i32 in {{.*}}.main.o
+# ARCHIVE-NEXT: >>> defined as (f32) -> i32 in {{.*}}.ret32.o
+
 # ERROR: error: function signature mismatch: ret32
 # ERROR-NEXT: >>> defined as (i32, i64, i32) -> i32 in {{.*}}.main.o
 # ERROR-NEXT: >>> defined as (f32) -> i32 in {{.*}}.ret32.o
@@ -56,7 +65,7 @@ ret32_address_main:
 
 # YAML:        - Type:            CUSTOM
 # YAML-NEXT:     Name:            name
-# YAML-NEXT:     FunctionNames:   
+# YAML-NEXT:     FunctionNames:
 # YAML-NEXT:       - Index:           0
 # YAML-NEXT:         Name:            'signature_mismatch:ret32'
 # YAML-NEXT:       - Index:           1
diff --git a/lld/wasm/SymbolTable.cpp b/lld/wasm/SymbolTable.cpp
index c98aa3ee3a7a320..c000d5d3b97dc0d 100644
--- a/lld/wasm/SymbolTable.cpp
+++ b/lld/wasm/SymbolTable.cpp
@@ -749,7 +749,7 @@ void SymbolTable::addLazy(StringRef name, InputFile *file) {
   std::tie(s, wasInserted) = insertName(name);
 
   if (wasInserted) {
-    replaceSymbol<LazySymbol>(s, name, 0, file);
+    replaceSymbol<LazySymbol>(s, name, file);
     return;
   }
 
@@ -767,14 +767,14 @@ void SymbolTable::addLazy(StringRef name, InputFile *file) {
       oldSig = f->signature;
     LLVM_DEBUG(dbgs() << "replacing existing weak undefined symbol\n");
     auto newSym =
-        replaceSymbol<LazySymbol>(s, name, WASM_SYMBOL_BINDING_WEAK, file);
+        replaceSymbol<LazySymbol>(s, name, file, WASM_SYMBOL_BINDING_WEAK);
     newSym->signature = oldSig;
     return;
   }
 
   LLVM_DEBUG(dbgs() << "replacing existing undefined\n");
   const InputFile *oldFile = s->getFile();
-  replaceSymbol<LazySymbol>(s, name, 0, file)->extract();
+  LazySymbol(name, file).extract();
   if (!config->whyExtract.empty())
     ctx.whyExtractRecords.emplace_back(toString(oldFile), s->getFile(), *s);
 }
diff --git a/lld/wasm/Symbols.h b/lld/wasm/Symbols.h
index de52c92d34e78b0..9908f23f38695b8 100644
--- a/lld/wasm/Symbols.h
+++ b/lld/wasm/Symbols.h
@@ -497,7 +497,7 @@ class UndefinedTag : public TagSymbol {
 // symbols into consideration.
 class LazySymbol : public Symbol {
 public:
-  LazySymbol(StringRef name, uint32_t flags, InputFile *file)
+  LazySymbol(StringRef name, InputFile *file, uint8_t flags = 0)
       : Symbol(name, LazyKind, flags, file) {}
 
   static bool classof(const Symbol *s) { return s->kind() == LazyKind; }

``````````

</details>


https://github.com/llvm/llvm-project/pull/78831