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[ELF] Initialize Symbol fields in the constructor instead of via memset (#198129)

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`initSectionsAndLocalSyms` and `makeDefined` memset the storage to zero
and then placement-new a Symbol-derived object into it. Placement new
begins a new object's lifetime. The standard does not seem to guarantee
the memset bytes carry into members the constructor leaves
uninitialized.

lld built by GCC 16 can make Valgrind report reads of Symbol::flags
(via getSymSectionIndex during finalizeSections) as uses of
uninitialized values (ClangBuiltLinux/linux#2162).

This patch reinstates the per-field initialization that commit
7787427605 ("[ELF] Avoid redundant assignment to Symbol fields. NFC")
had replaced with a bulk memset.

(cherry picked from commit 905a88b923)
This commit is contained in:
Fangrui Song 2026-05-16 14:38:18 -07:00 committed by Cullen Rhodes
parent 823afe0461
commit 4d5dffb594
2 changed files with 12 additions and 10 deletions
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2
lld/ELF/InputFiles.cpp
View file

@ -1261,7 +1261,6 @@ void ObjFile<ELFT>::initSectionsAndLocalSyms(bool ignoreComdats) {
if (!firstGlobal)
return;
SymbolUnion *locals = makeThreadLocalN<SymbolUnion>(firstGlobal);
memset(locals, 0, sizeof(SymbolUnion) * firstGlobal);
ArrayRef<Elf_Sym> eSyms = this->getELFSyms<ELFT>();
for (size_t i = 0, end = firstGlobal; i != end; ++i) {
@ -1297,7 +1296,6 @@ void ObjFile<ELFT>::initSectionsAndLocalSyms(bool ignoreComdats) {
else
new (symbols[i]) Defined(ctx, this, name, STB_LOCAL, eSym.st_other, type,
eSym.st_value, eSym.st_size, sec);
symbols[i]->partition = 1;
symbols[i]->isUsedInRegularObj = true;
}
}

20
lld/ELF/Symbols.h
View file

@ -102,7 +102,7 @@ public:
uint8_t symbolKind;
// The partition whose dynamic symbol table contains this symbol's definition.
uint8_t partition;
uint8_t partition = 1;
// True if this symbol is preemptible at load time.
//
@ -242,8 +242,13 @@ protected:
Symbol(Kind k, InputFile *file, StringRef name, uint8_t binding,
uint8_t stOther, uint8_t type)
: file(file), nameData(name.data()), nameSize(name.size()), type(type),
binding(binding), stOther(stOther), symbolKind(k), ltoCanOmit(false),
archSpecificBit(false) {}
binding(binding), stOther(stOther), symbolKind(k), isPreemptible(false),
isUsedInRegularObj(false), isExported(false), ltoCanOmit(false),
traced(false), hasVersionSuffix(false), isInIplt(false),
gotInIgot(false), folded(false), archSpecificBit(false),
scriptDefined(false), dsoDefined(false), dsoProtected(false),
versionScriptAssigned(false), thunkAccessed(false),
inDynamicList(false), referenced(false), referencedAfterWrap(false) {}
void overwrite(Symbol &sym, Kind k) const {
if (sym.traced)
@ -302,12 +307,12 @@ public:
// Temporary flags used to communicate which symbol entries need PLT and GOT
// entries during postScanRelocations();
std::atomic<uint16_t> flags;
std::atomic<uint16_t> flags = 0;
// A ctx.symAux index used to access GOT/PLT entry indexes. This is allocated
// in postScanRelocations().
uint32_t auxIdx;
uint32_t dynsymIndex;
uint32_t auxIdx = 0;
uint32_t dynsymIndex = 0;
// If `file` is SharedFile (for SharedSymbol or copy-relocated Defined), this
// represents the Verdef index within the input DSO, which will be converted
@ -315,7 +320,7 @@ public:
// index (VER_NDX_LOCAL, VER_NDX_GLOBAL, or a named version).
// VER_NDX_LOCAL indicates a defined symbol that has been localized by a
// version script's local: directive or --exclude-libs.
uint16_t versionId;
uint16_t versionId = 0;
LLVM_PREFERRED_TYPE(bool)
uint8_t versionScriptAssigned : 1;
@ -526,7 +531,6 @@ union SymbolUnion {
template <typename... T> Defined *makeDefined(T &&...args) {
auto *sym = getSpecificAllocSingleton<SymbolUnion>().Allocate();
memset(sym, 0, sizeof(Symbol));
auto &s = *new (reinterpret_cast<Defined *>(sym)) Defined(std::forward<T>(args)...);
return &s;
}