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release/20.x: [wasm-ld] Refactor WasmSym from static globals to per-link context (#134970) #137620

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Merged
merged 1 commit into from
May 10, 2025
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release/20.x: [wasm-ld] Refactor WasmSym from static globals to per-link context (#134970) #137620

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106 changes: 106 additions & 0 deletions lld/wasm/Config.h
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,11 @@ class InputTable;
class InputGlobal;
class InputFunction;
class Symbol;
class DefinedData;
class GlobalSymbol;
class DefinedFunction;
class UndefinedGlobal;
class TableSymbol;

// For --unresolved-symbols.
enum class UnresolvedPolicy { ReportError, Warn, Ignore, ImportDynamic };
Expand Down Expand Up @@ -139,6 +144,107 @@ struct Ctx {
llvm::SmallVector<InputGlobal *, 0> syntheticGlobals;
llvm::SmallVector<InputTable *, 0> syntheticTables;

// linker-generated symbols
struct WasmSym {
// __global_base
// Symbol marking the start of the global section.
DefinedData *globalBase;

// __stack_pointer/__stack_low/__stack_high
// Global that holds current value of stack pointer and data symbols marking
// the start and end of the stack region. stackPointer is initialized to
// stackHigh and grows downwards towards stackLow
GlobalSymbol *stackPointer;
DefinedData *stackLow;
DefinedData *stackHigh;

// __tls_base
// Global that holds the address of the base of the current thread's
// TLS block.
GlobalSymbol *tlsBase;

// __tls_size
// Symbol whose value is the size of the TLS block.
GlobalSymbol *tlsSize;

// __tls_size
// Symbol whose value is the alignment of the TLS block.
GlobalSymbol *tlsAlign;

// __data_end
// Symbol marking the end of the data and bss.
DefinedData *dataEnd;

// __heap_base/__heap_end
// Symbols marking the beginning and end of the "heap". It starts at the end
// of the data, bss and explicit stack, and extends to the end of the linear
// memory allocated by wasm-ld. This region of memory is not used by the
// linked code, so it may be used as a backing store for `sbrk` or `malloc`
// implementations.
DefinedData *heapBase;
DefinedData *heapEnd;

// __wasm_init_memory_flag
// Symbol whose contents are nonzero iff memory has already been
// initialized.
DefinedData *initMemoryFlag;

// __wasm_init_memory
// Function that initializes passive data segments during instantiation.
DefinedFunction *initMemory;

// __wasm_call_ctors
// Function that directly calls all ctors in priority order.
DefinedFunction *callCtors;

// __wasm_call_dtors
// Function that calls the libc/etc. cleanup function.
DefinedFunction *callDtors;

// __wasm_apply_global_relocs
// Function that applies relocations to wasm globals post-instantiation.
// Unlike __wasm_apply_data_relocs this needs to run on every thread.
DefinedFunction *applyGlobalRelocs;

// __wasm_apply_tls_relocs
// Like __wasm_apply_data_relocs but for TLS section. These must be
// delayed until __wasm_init_tls.
DefinedFunction *applyTLSRelocs;

// __wasm_apply_global_tls_relocs
// Like applyGlobalRelocs but for globals that hold TLS addresses. These
// must be delayed until __wasm_init_tls.
DefinedFunction *applyGlobalTLSRelocs;

// __wasm_init_tls
// Function that allocates thread-local storage and initializes it.
DefinedFunction *initTLS;

// Pointer to the function that is to be used in the start section.
// (normally an alias of initMemory, or applyGlobalRelocs).
DefinedFunction *startFunction;

// __dso_handle
// Symbol used in calls to __cxa_atexit to determine current DLL
DefinedData *dsoHandle;

// __table_base
// Used in PIC code for offset of indirect function table
UndefinedGlobal *tableBase;
DefinedData *definedTableBase;

// __memory_base
// Used in PIC code for offset of global data
UndefinedGlobal *memoryBase;
DefinedData *definedMemoryBase;

// __indirect_function_table
// Used as an address space for function pointers, with each function that
// is used as a function pointer being allocated a slot.
TableSymbol *indirectFunctionTable;
};
WasmSym sym;

// True if we are creating position-independent code.
bool isPic = false;

Expand Down
60 changes: 30 additions & 30 deletions lld/wasm/Driver.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,7 @@ void Ctx::reset() {
isPic = false;
legacyFunctionTable = false;
emitBssSegments = false;
sym = WasmSym{};
}

namespace {
Expand Down Expand Up @@ -941,14 +942,14 @@ static void createSyntheticSymbols() {
true};
static llvm::wasm::WasmGlobalType mutableGlobalTypeI64 = {WASM_TYPE_I64,
true};
WasmSym::callCtors = symtab->addSyntheticFunction(
ctx.sym.callCtors = symtab->addSyntheticFunction(
"__wasm_call_ctors", WASM_SYMBOL_VISIBILITY_HIDDEN,
make<SyntheticFunction>(nullSignature, "__wasm_call_ctors"));

bool is64 = ctx.arg.is64.value_or(false);

if (ctx.isPic) {
WasmSym::stackPointer =
ctx.sym.stackPointer =
createUndefinedGlobal("__stack_pointer", ctx.arg.is64.value_or(false)
? &mutableGlobalTypeI64
: &mutableGlobalTypeI32);
Expand All @@ -958,45 +959,44 @@ static void createSyntheticSymbols() {
// See:
// https://github.com/WebAssembly/tool-conventions/blob/main/DynamicLinking.md
auto *globalType = is64 ? &globalTypeI64 : &globalTypeI32;
WasmSym::memoryBase = createUndefinedGlobal("__memory_base", globalType);
WasmSym::tableBase = createUndefinedGlobal("__table_base", globalType);
WasmSym::memoryBase->markLive();
WasmSym::tableBase->markLive();
ctx.sym.memoryBase = createUndefinedGlobal("__memory_base", globalType);
ctx.sym.tableBase = createUndefinedGlobal("__table_base", globalType);
ctx.sym.memoryBase->markLive();
ctx.sym.tableBase->markLive();
} else {
// For non-PIC code
WasmSym::stackPointer = createGlobalVariable("__stack_pointer", true);
WasmSym::stackPointer->markLive();
ctx.sym.stackPointer = createGlobalVariable("__stack_pointer", true);
ctx.sym.stackPointer->markLive();
}

if (ctx.arg.sharedMemory) {
WasmSym::tlsBase = createGlobalVariable("__tls_base", true);
WasmSym::tlsSize = createGlobalVariable("__tls_size", false);
WasmSym::tlsAlign = createGlobalVariable("__tls_align", false);
WasmSym::initTLS = symtab->addSyntheticFunction(
ctx.sym.tlsBase = createGlobalVariable("__tls_base", true);
ctx.sym.tlsSize = createGlobalVariable("__tls_size", false);
ctx.sym.tlsAlign = createGlobalVariable("__tls_align", false);
ctx.sym.initTLS = symtab->addSyntheticFunction(
"__wasm_init_tls", WASM_SYMBOL_VISIBILITY_HIDDEN,
make<SyntheticFunction>(
is64 ? i64ArgSignature : i32ArgSignature,
"__wasm_init_tls"));
make<SyntheticFunction>(is64 ? i64ArgSignature : i32ArgSignature,
"__wasm_init_tls"));
}
}

static void createOptionalSymbols() {
if (ctx.arg.relocatable)
return;

WasmSym::dsoHandle = symtab->addOptionalDataSymbol("__dso_handle");
ctx.sym.dsoHandle = symtab->addOptionalDataSymbol("__dso_handle");

if (!ctx.arg.shared)
WasmSym::dataEnd = symtab->addOptionalDataSymbol("__data_end");
ctx.sym.dataEnd = symtab->addOptionalDataSymbol("__data_end");

if (!ctx.isPic) {
WasmSym::stackLow = symtab->addOptionalDataSymbol("__stack_low");
WasmSym::stackHigh = symtab->addOptionalDataSymbol("__stack_high");
WasmSym::globalBase = symtab->addOptionalDataSymbol("__global_base");
WasmSym::heapBase = symtab->addOptionalDataSymbol("__heap_base");
WasmSym::heapEnd = symtab->addOptionalDataSymbol("__heap_end");
WasmSym::definedMemoryBase = symtab->addOptionalDataSymbol("__memory_base");
WasmSym::definedTableBase = symtab->addOptionalDataSymbol("__table_base");
ctx.sym.stackLow = symtab->addOptionalDataSymbol("__stack_low");
ctx.sym.stackHigh = symtab->addOptionalDataSymbol("__stack_high");
ctx.sym.globalBase = symtab->addOptionalDataSymbol("__global_base");
ctx.sym.heapBase = symtab->addOptionalDataSymbol("__heap_base");
ctx.sym.heapEnd = symtab->addOptionalDataSymbol("__heap_end");
ctx.sym.definedMemoryBase = symtab->addOptionalDataSymbol("__memory_base");
ctx.sym.definedTableBase = symtab->addOptionalDataSymbol("__table_base");
}

// For non-shared memory programs we still need to define __tls_base since we
Expand All @@ -1009,7 +1009,7 @@ static void createOptionalSymbols() {
// __tls_size and __tls_align are not needed in this case since they are only
// needed for __wasm_init_tls (which we do not create in this case).
if (!ctx.arg.sharedMemory)
WasmSym::tlsBase = createOptionalGlobal("__tls_base", false);
ctx.sym.tlsBase = createOptionalGlobal("__tls_base", false);
}

static void processStubLibrariesPreLTO() {
Expand Down Expand Up @@ -1384,9 +1384,9 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
// by libc/etc., because destructors are registered dynamically with
// `__cxa_atexit` and friends.
if (!ctx.arg.relocatable && !ctx.arg.shared &&
!WasmSym::callCtors->isUsedInRegularObj &&
WasmSym::callCtors->getName() != ctx.arg.entry &&
!ctx.arg.exportedSymbols.count(WasmSym::callCtors->getName())) {
!ctx.sym.callCtors->isUsedInRegularObj &&
ctx.sym.callCtors->getName() != ctx.arg.entry &&
!ctx.arg.exportedSymbols.count(ctx.sym.callCtors->getName())) {
if (Symbol *callDtors =
handleUndefined("__wasm_call_dtors", "<internal>")) {
if (auto *callDtorsFunc = dyn_cast<DefinedFunction>(callDtors)) {
Expand All @@ -1395,7 +1395,7 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
!callDtorsFunc->signature->Returns.empty())) {
error("__wasm_call_dtors must have no argument or return values");
}
WasmSym::callDtors = callDtorsFunc;
ctx.sym.callDtors = callDtorsFunc;
} else {
error("__wasm_call_dtors must be a function");
}
Expand Down Expand Up @@ -1488,7 +1488,7 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
markLive();

// Provide the indirect function table if needed.
WasmSym::indirectFunctionTable =
ctx.sym.indirectFunctionTable =
symtab->resolveIndirectFunctionTable(/*required =*/false);

if (errorCount())
Expand Down
10 changes: 5 additions & 5 deletions lld/wasm/InputChunks.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -397,9 +397,9 @@ bool InputChunk::generateRelocationCode(raw_ostream &os) const {
if (ctx.isPic) {
writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
if (isTLS())
writeUleb128(os, WasmSym::tlsBase->getGlobalIndex(), "tls_base");
writeUleb128(os, ctx.sym.tlsBase->getGlobalIndex(), "tls_base");
else
writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(), "memory_base");
writeUleb128(os, ctx.sym.memoryBase->getGlobalIndex(), "memory_base");
writeU8(os, opcode_ptr_add, "ADD");
}

Expand All @@ -422,12 +422,12 @@ bool InputChunk::generateRelocationCode(raw_ostream &os) const {
}
} else {
assert(ctx.isPic);
const GlobalSymbol* baseSymbol = WasmSym::memoryBase;
const GlobalSymbol *baseSymbol = ctx.sym.memoryBase;
if (rel.Type == R_WASM_TABLE_INDEX_I32 ||
rel.Type == R_WASM_TABLE_INDEX_I64)
baseSymbol = WasmSym::tableBase;
baseSymbol = ctx.sym.tableBase;
else if (sym->isTLS())
baseSymbol = WasmSym::tlsBase;
baseSymbol = ctx.sym.tlsBase;
writeU8(os, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
writeUleb128(os, baseSymbol->getGlobalIndex(), "base");
writeU8(os, opcode_reloc_const, "CONST");
Expand Down
6 changes: 3 additions & 3 deletions lld/wasm/MarkLive.cpp
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Expand Up @@ -114,8 +114,8 @@ void MarkLive::run() {
if (sym->isNoStrip() || sym->isExported())
enqueue(sym);

if (WasmSym::callDtors)
enqueue(WasmSym::callDtors);
if (ctx.sym.callDtors)
enqueue(ctx.sym.callDtors);

for (const ObjFile *obj : ctx.objectFiles)
if (obj->isLive()) {
Expand All @@ -131,7 +131,7 @@ void MarkLive::run() {
// If we have any non-discarded init functions, mark `__wasm_call_ctors` as
// live so that we assign it an index and call it.
if (isCallCtorsLive())
WasmSym::callCtors->markLive();
ctx.sym.callCtors->markLive();
}

void MarkLive::mark() {
Expand Down
4 changes: 2 additions & 2 deletions lld/wasm/OutputSections.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -123,7 +123,7 @@ void DataSection::finalizeContents() {
if ((segment->initFlags & WASM_DATA_SEGMENT_IS_PASSIVE) == 0) {
if (ctx.isPic && ctx.arg.extendedConst) {
writeU8(os, WASM_OPCODE_GLOBAL_GET, "global get");
writeUleb128(os, WasmSym::memoryBase->getGlobalIndex(),
writeUleb128(os, ctx.sym.memoryBase->getGlobalIndex(),
"literal (global index)");
if (segment->startVA) {
writePtrConst(os, segment->startVA, is64, "offset");
Expand All @@ -136,7 +136,7 @@ void DataSection::finalizeContents() {
if (ctx.isPic) {
assert(segment->startVA == 0);
initExpr.Inst.Opcode = WASM_OPCODE_GLOBAL_GET;
initExpr.Inst.Value.Global = WasmSym::memoryBase->getGlobalIndex();
initExpr.Inst.Value.Global = ctx.sym.memoryBase->getGlobalIndex();
} else {
initExpr = intConst(segment->startVA, is64);
}
Expand Down
25 changes: 0 additions & 25 deletions lld/wasm/Symbols.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -77,31 +77,6 @@ std::string toString(wasm::Symbol::Kind kind) {
}

namespace wasm {
DefinedFunction *WasmSym::callCtors;
DefinedFunction *WasmSym::callDtors;
DefinedFunction *WasmSym::initMemory;
DefinedFunction *WasmSym::applyGlobalRelocs;
DefinedFunction *WasmSym::applyTLSRelocs;
DefinedFunction *WasmSym::applyGlobalTLSRelocs;
DefinedFunction *WasmSym::initTLS;
DefinedFunction *WasmSym::startFunction;
DefinedData *WasmSym::dsoHandle;
DefinedData *WasmSym::dataEnd;
DefinedData *WasmSym::globalBase;
DefinedData *WasmSym::heapBase;
DefinedData *WasmSym::heapEnd;
DefinedData *WasmSym::initMemoryFlag;
GlobalSymbol *WasmSym::stackPointer;
DefinedData *WasmSym::stackLow;
DefinedData *WasmSym::stackHigh;
GlobalSymbol *WasmSym::tlsBase;
GlobalSymbol *WasmSym::tlsSize;
GlobalSymbol *WasmSym::tlsAlign;
UndefinedGlobal *WasmSym::tableBase;
DefinedData *WasmSym::definedTableBase;
UndefinedGlobal *WasmSym::memoryBase;
DefinedData *WasmSym::definedMemoryBase;
TableSymbol *WasmSym::indirectFunctionTable;

WasmSymbolType Symbol::getWasmType() const {
if (isa<FunctionSymbol>(this))
Expand Down
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