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904e03b711
lld relies on a memset that GCC 16 is allowed to optimize away, leaving some symbol fields uninitialized. With lld 21, this makes `ld -r` emit broken section symbols, which breaks LTO kernel module builds (see ClangBuiltLinux/linux#2162). 18 through 20 should have the same bug, but I haven't seen it break there myself. This backports llvm/llvm-project@4d5dffb594 and llvm/llvm-project@070e505ce2, which landed in 22.1.8.
102 lines
3.9 KiB
Diff
102 lines
3.9 KiB
Diff
From 4d5dffb59420df29cc3b419a7fc90834aed7f7a9 Mon Sep 17 00:00:00 2001
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From: Fangrui Song <i@maskray.me>
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Date: Sat, 16 May 2026 21:38:18 +0000
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Subject: [PATCH] [ELF] Initialize Symbol fields in the constructor instead of
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via memset (#198129)
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`initSectionsAndLocalSyms` and `makeDefined` memset the storage to zero
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and then placement-new a Symbol-derived object into it. Placement new
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begins a new object's lifetime. The standard does not seem to guarantee
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the memset bytes carry into members the constructor leaves
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uninitialized.
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lld built by GCC 16 can make Valgrind report reads of Symbol::flags
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(via getSymSectionIndex during finalizeSections) as uses of
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uninitialized values (ClangBuiltLinux/linux#2162).
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This patch reinstates the per-field initialization that commit
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778742760534 ("[ELF] Avoid redundant assignment to Symbol fields. NFC")
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had replaced with a bulk memset.
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(cherry picked from commit 905a88b923433eb8cd83677ea55bee82eb9ba498)
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Squashed with 070e505ce21d ("[LLD][ELF] Add missing initialization of
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Symbol `used` member.") and rebased onto 20.1.8.
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---
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--- a/ELF/InputFiles.cpp
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+++ b/ELF/InputFiles.cpp
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@@ -1175,7 +1175,6 @@
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if (!firstGlobal)
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return;
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SymbolUnion *locals = makeThreadLocalN<SymbolUnion>(firstGlobal);
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- memset(locals, 0, sizeof(SymbolUnion) * firstGlobal);
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ArrayRef<Elf_Sym> eSyms = this->getELFSyms<ELFT>();
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for (size_t i = 0, end = firstGlobal; i != end; ++i) {
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@@ -1211,7 +1210,6 @@
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else
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new (symbols[i]) Defined(ctx, this, name, STB_LOCAL, eSym.st_other, type,
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eSym.st_value, eSym.st_size, sec);
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- symbols[i]->partition = 1;
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symbols[i]->isUsedInRegularObj = true;
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}
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}
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--- a/ELF/Symbols.h
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+++ b/ELF/Symbols.h
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@@ -102,7 +102,7 @@
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uint8_t symbolKind;
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// The partition whose dynamic symbol table contains this symbol's definition.
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- uint8_t partition;
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+ uint8_t partition = 1;
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// True if this symbol is preemptible at load time.
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//
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@@ -242,8 +242,13 @@
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Symbol(Kind k, InputFile *file, StringRef name, uint8_t binding,
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uint8_t stOther, uint8_t type)
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: file(file), nameData(name.data()), nameSize(name.size()), type(type),
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- binding(binding), stOther(stOther), symbolKind(k), ltoCanOmit(false),
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- archSpecificBit(false) {}
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+ binding(binding), stOther(stOther), symbolKind(k), isPreemptible(false),
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+ isUsedInRegularObj(false), used(false), isExported(false),
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+ ltoCanOmit(false), traced(false), hasVersionSuffix(false),
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+ isInIplt(false), gotInIgot(false), folded(false),
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+ archSpecificBit(false), scriptDefined(false), dsoDefined(false),
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+ dsoProtected(false), versionScriptAssigned(false), thunkAccessed(false),
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+ inDynamicList(false), referenced(false), referencedAfterWrap(false) {}
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void overwrite(Symbol &sym, Kind k) const {
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if (sym.traced)
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@@ -302,18 +307,18 @@
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// Temporary flags used to communicate which symbol entries need PLT and GOT
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// entries during postScanRelocations();
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- std::atomic<uint16_t> flags;
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+ std::atomic<uint16_t> flags = 0;
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// A ctx.symAux index used to access GOT/PLT entry indexes. This is allocated
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// in postScanRelocations().
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- uint32_t auxIdx;
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- uint32_t dynsymIndex;
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+ uint32_t auxIdx = 0;
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+ uint32_t dynsymIndex = 0;
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// If `file` is SharedFile (for SharedSymbol or copy-relocated Defined), this
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// represents the Verdef index within the input DSO, which will be converted
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// to a Verneed index in the output. Otherwise, this represents the Verdef
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// index (VER_NDX_LOCAL, VER_NDX_GLOBAL, or a named version).
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- uint16_t versionId;
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+ uint16_t versionId = 0;
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LLVM_PREFERRED_TYPE(bool)
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uint8_t versionScriptAssigned : 1;
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@@ -524,7 +529,6 @@
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template <typename... T> Defined *makeDefined(T &&...args) {
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auto *sym = getSpecificAllocSingleton<SymbolUnion>().Allocate();
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- memset(sym, 0, sizeof(Symbol));
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auto &s = *new (reinterpret_cast<Defined *>(sym)) Defined(std::forward<T>(args)...);
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return &s;
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}
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