[lld] [LLD] [COFF] Zero-intialization & proper constructor invocation in COFF's Symbol (PR #98447)

[Vikash Gupta via llvm-commits]

https://github.com/vg0204 updated https://github.com/llvm/llvm-project/pull/98447

>From 205dbe759d3517bb01cd268544ffb57d7891deef Mon Sep 17 00:00:00 2001
From: vg0204 <Vikash.Gupta at amd.com>
Date: Thu, 11 Jul 2024 14:05:34 +0530
Subject: [PATCH] [LLD] Zero-initialization & explicit set-up of
 isUsedinRegObject in Symbol class

It happened due to lld's COFF linker multiple regression tests failure.
It got reliably reproduced after the needed intialization of
isUsedinRegularObject bit in the Symbol's ctor, but not handled at
replaceSymbol API properly while creating a specific symbol to insert in
symbol table.

Eventually, the issue was about not handling exported symbols properly,
when dealing with defining undefined symbols for COFF linker. It got
resolved by explicit setting up the isUsedinRegularObject bit around the
ctor invocation of symbol class in replaceSymbol API.
---
 lld/COFF/Symbols.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lld/COFF/Symbols.h b/lld/COFF/Symbols.h
index 5ef46f5af6a6c..56b137d56873a 100644
--- a/lld/COFF/Symbols.h
+++ b/lld/COFF/Symbols.h
@@ -98,10 +98,10 @@ class Symbol {
   friend SymbolTable;
   explicit Symbol(Kind k, StringRef n = "")
       : symbolKind(k), isExternal(true), isCOMDAT(false),
-        writtenToSymtab(false), pendingArchiveLoad(false), isGCRoot(false),
-        isRuntimePseudoReloc(false), deferUndefined(false), canInline(true),
-        isWeak(false), nameSize(n.size()),
-        nameData(n.empty() ? nullptr : n.data()) {
+        writtenToSymtab(false), isUsedInRegularObj(false),
+        pendingArchiveLoad(false), isGCRoot(false), isRuntimePseudoReloc(false),
+        deferUndefined(false), canInline(true), isWeak(false),
+        nameSize(n.size()), nameData(n.empty() ? nullptr : n.data()) {
     assert((!n.empty() || k <= LastDefinedCOFFKind) &&
            "If the name is empty, the Symbol must be a DefinedCOFF.");
   }
@@ -499,8 +499,10 @@ void replaceSymbol(Symbol *s, ArgT &&... arg) {
   assert(static_cast<Symbol *>(static_cast<T *>(nullptr)) == nullptr &&
          "Not a Symbol");
   bool canInline = s->canInline;
+  bool isUsedInRegularObj = s->isUsedInRegularObj;
   new (s) T(std::forward<ArgT>(arg)...);
   s->canInline = canInline;
+  s->isUsedInRegularObj = isUsedInRegularObj;
 }
 } // namespace coff