[lld] r366272 - [WebAssembly] Implement thread-local storage (local-exec model)
Guanzhong Chen via llvm-commits
llvm-commits at lists.llvm.org
Tue Jul 16 15:00:46 PDT 2019
Author: quantum
Date: Tue Jul 16 15:00:45 2019
New Revision: 366272
URL: http://llvm.org/viewvc/llvm-project?rev=366272&view=rev
Log:
[WebAssembly] Implement thread-local storage (local-exec model)
Summary:
Thread local variables are placed inside a `.tdata` segment. Their symbols are
offsets from the start of the segment. The address of a thread local variable
is computed as `__tls_base` + the offset from the start of the segment.
`.tdata` segment is a passive segment and `memory.init` is used once per thread
to initialize the thread local storage.
`__tls_base` is a wasm global. Since each thread has its own wasm instance,
it is effectively thread local. Currently, `__tls_base` must be initialized
at thread startup, and so cannot be used with dynamic libraries.
`__tls_base` is to be initialized with a new linker-synthesized function,
`__wasm_init_tls`, which takes as an argument a block of memory to use as the
storage for thread locals. It then initializes the block of memory and sets
`__tls_base`. As `__wasm_init_tls` will handle the memory initialization,
the memory does not have to be zeroed.
To help allocating memory for thread-local storage, a new compiler intrinsic
is introduced: `__builtin_wasm_tls_size()`. This instrinsic function returns
the size of the thread-local storage for the current function.
The expected usage is to run something like the following upon thread startup:
__wasm_init_tls(malloc(__builtin_wasm_tls_size()));
Reviewers: tlively, aheejin, kripken, sbc100
Subscribers: dschuff, jgravelle-google, hiraditya, sunfish, jfb, cfe-commits, llvm-commits
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D64537
Added:
lld/trunk/test/wasm/tls.ll
Modified:
lld/trunk/test/wasm/data-segments.ll
lld/trunk/wasm/Driver.cpp
lld/trunk/wasm/Symbols.cpp
lld/trunk/wasm/Symbols.h
lld/trunk/wasm/Writer.cpp
Modified: lld/trunk/test/wasm/data-segments.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/wasm/data-segments.ll?rev=366272&r1=366271&r2=366272&view=diff
==============================================================================
--- lld/trunk/test/wasm/data-segments.ll (original)
+++ lld/trunk/test/wasm/data-segments.ll Tue Jul 16 15:00:45 2019
@@ -4,11 +4,11 @@
; atomics => active segments (TODO: error)
; RUN: wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.o -o %t.atomics.wasm
-; RUN: obj2yaml %t.atomics.wasm | FileCheck %s --check-prefix ACTIVE
+; RUN: obj2yaml %t.atomics.wasm | FileCheck %s --check-prefixes ACTIVE,ACTIVE-TLS
; atomics, active segments => active segments
; RUN: wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 --active-segments %t.atomics.o -o %t.atomics.active.wasm
-; RUN: obj2yaml %t.atomics.active.wasm | FileCheck %s --check-prefix ACTIVE
+; RUN: obj2yaml %t.atomics.active.wasm | FileCheck %s --check-prefixes ACTIVE,ACTIVE-TLS
; atomics, passive segments => error
; RUN: not wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 --passive-segments %t.atomics.o -o %t.atomics.passive.wasm 2>&1 | FileCheck %s --check-prefix ERROR
@@ -27,15 +27,15 @@
; atomics, bulk memory => active segments (TODO: passive)
; RUN: wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.o -o %t.atomics.bulk-mem.wasm
-; RUN: obj2yaml %t.atomics.bulk-mem.wasm | FileCheck %s --check-prefix ACTIVE
+; RUN: obj2yaml %t.atomics.bulk-mem.wasm | FileCheck %s --check-prefixes ACTIVE,ACTIVE-TLS
; atomics, bulk memory, active segments => active segments
; RUN: wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 --active-segments %t.atomics.bulk-mem.o -o %t.atomics.bulk-mem.active.wasm
-; RUN: obj2yaml %t.atomics.bulk-mem.active.wasm | FileCheck %s --check-prefix ACTIVE
+; RUN: obj2yaml %t.atomics.bulk-mem.active.wasm | FileCheck %s --check-prefixes ACTIVE,ACTIVE-TLS
; atomics, bulk memory, passive segments => passive segments
; RUN: wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 --passive-segments %t.atomics.bulk-mem.o -o %t.atomics.bulk-mem.passive.wasm
-; RUN: obj2yaml %t.atomics.bulk-mem.passive.wasm | FileCheck %s --check-prefix PASSIVE
+; RUN: obj2yaml %t.atomics.bulk-mem.passive.wasm | FileCheck %s --check-prefixes PASSIVE,PASSIVE-TLS
target triple = "wasm32-unknown-unknown"
@@ -54,6 +54,9 @@ target triple = "wasm32-unknown-unknown"
; ACTIVE-NEXT: - Index: 0
; ACTIVE-NEXT: Locals: []
; ACTIVE-NEXT: Body: 0B
+; ACTIVE-TLS-NEXT: - Index: 1
+; ACTIVE-TLS-NEXT: Locals: []
+; ACTIVE-TLS-NEXT: Body: 0B
; ACTIVE-NEXT: - Type: DATA
; ACTIVE-NEXT: Segments:
; ACTIVE-NEXT: - SectionOffset: 7
@@ -80,6 +83,8 @@ target triple = "wasm32-unknown-unknown"
; ACTIVE-NEXT: FunctionNames:
; ACTIVE-NEXT: - Index: 0
; ACTIVE-NEXT: Name: __wasm_call_ctors
+; ACTIVE-TLS-NEXT: - Index: 1
+; ACTIVE-TLS-NEXT: Name: __wasm_init_tls
; PASSIVE-LABEL: - Type: CODE
; PASSIVE-NEXT: Functions:
@@ -89,6 +94,9 @@ target triple = "wasm32-unknown-unknown"
; PASSIVE-NEXT: - Index: 1
; PASSIVE-NEXT: Locals: []
; PASSIVE-NEXT: Body: 41800841004114FC080000FC090041940841004190CE00FC080100FC090141A4D6004100410DFC080200FC09020B
+; PASSIVE-TLS-NEXT: - Index: 2
+; PASSIVE-TLS-NEXT: Locals: []
+; PASSIVE-TLS-NEXT: Body: 0B
; PASSIVE-NEXT: - Type: DATA
; PASSIVE-NEXT: Segments:
; PASSIVE-NEXT: - SectionOffset: 3
@@ -108,3 +116,5 @@ target triple = "wasm32-unknown-unknown"
; PASSIVE-NEXT: Name: __wasm_call_ctors
; PASSIVE-NEXT: - Index: 1
; PASSIVE-NEXT: Name: __wasm_init_memory
+; PASSIVE-TLS-NEXT: - Index: 2
+; PASSIVE-TLS-NEXT: Name: __wasm_init_tls
Added: lld/trunk/test/wasm/tls.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/wasm/tls.ll?rev=366272&view=auto
==============================================================================
--- lld/trunk/test/wasm/tls.ll (added)
+++ lld/trunk/test/wasm/tls.ll Tue Jul 16 15:00:45 2019
@@ -0,0 +1,81 @@
+; RUN: llc -mattr=+bulk-memory -filetype=obj %s -o %t.o
+
+target triple = "wasm32-unknown-unknown"
+
+ at tls1 = thread_local(localexec) global i32 1, align 4
+ at no_tls = global i32 0, align 4
+ at tls2 = thread_local(localexec) global i32 1, align 4
+
+define i32* @tls1_addr() {
+ ret i32* @tls1
+}
+
+define i32* @tls2_addr() {
+ ret i32* @tls2
+}
+
+; RUN: wasm-ld -no-gc-sections --shared-memory --max-memory=131072 --no-entry -o %t.wasm %t.o
+; RUN: obj2yaml %t.wasm | FileCheck %s
+
+; RUN: wasm-ld -no-gc-sections --shared-memory --max-memory=131072 --no-merge-data-segments --no-entry -o %t.wasm %t.o
+; RUN: obj2yaml %t.wasm | FileCheck %s
+
+; CHECK: - Type: GLOBAL
+; CHECK-NEXT: Globals:
+; CHECK-NEXT: - Index: 0
+; CHECK-NEXT: Type: I32
+; CHECK-NEXT: Mutable: true
+; CHECK-NEXT: InitExpr:
+; CHECK-NEXT: Opcode: I32_CONST
+; CHECK-NEXT: Value: 66576
+; CHECK-NEXT: - Index: 1
+; CHECK-NEXT: Type: I32
+; CHECK-NEXT: Mutable: true
+; CHECK-NEXT: InitExpr:
+; CHECK-NEXT: Opcode: I32_CONST
+; CHECK-NEXT: Value: 0
+; CHECK-NEXT: - Index: 2
+; CHECK-NEXT: Type: I32
+; CHECK-NEXT: Mutable: false
+; CHECK-NEXT: InitExpr:
+; CHECK-NEXT: Opcode: I32_CONST
+; CHECK-NEXT: Value: 8
+
+
+; CHECK: - Type: CODE
+; CHECK-NEXT: Functions:
+; CHECK-NEXT: - Index: 0
+; CHECK-NEXT: Locals: []
+; CHECK-NEXT: Body: 0B
+; CHECK-NEXT: - Index: 1
+; CHECK-NEXT: Locals: []
+; CHECK-NEXT: Body: 20002401200041004108FC0800000B
+
+; Expected body of __wasm_init_tls:
+; local.get 0
+; global.set 1
+; local.get 0
+; i32.const 0
+; i32.const 8
+; memory.init 0, 0
+; end
+
+; CHECK-NEXT: - Index: 2
+; CHECK-NEXT: Locals: []
+; CHECK-NEXT: Body: 2381808080004180808080006A0B
+
+; Expected body of tls1_addr:
+; global.get 1
+; i32.const 0
+; i32.add
+; end
+
+; CHECK-NEXT: - Index: 3
+; CHECK-NEXT: Locals: []
+; CHECK-NEXT: Body: 2381808080004184808080006A0B
+
+; Expected body of tls1_addr:
+; global.get 1
+; i32.const 4
+; i32.add
+; end
Modified: lld/trunk/wasm/Driver.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Driver.cpp?rev=366272&r1=366271&r2=366272&view=diff
==============================================================================
--- lld/trunk/wasm/Driver.cpp (original)
+++ lld/trunk/wasm/Driver.cpp Tue Jul 16 15:00:45 2019
@@ -454,6 +454,7 @@ createUndefinedGlobal(StringRef name, ll
// Create ABI-defined synthetic symbols
static void createSyntheticSymbols() {
static WasmSignature nullSignature = {{}, {}};
+ static WasmSignature i32ArgSignature = {{}, {ValType::I32}};
static llvm::wasm::WasmGlobalType globalTypeI32 = {WASM_TYPE_I32, false};
static llvm::wasm::WasmGlobalType mutableGlobalTypeI32 = {WASM_TYPE_I32,
true};
@@ -516,6 +517,30 @@ static void createSyntheticSymbols() {
WasmSym::heapBase = symtab->addOptionalDataSymbol("__heap_base");
}
+ if (config->sharedMemory && !config->shared) {
+ llvm::wasm::WasmGlobal tlsBaseGlobal;
+ tlsBaseGlobal.Type = {WASM_TYPE_I32, true};
+ tlsBaseGlobal.InitExpr.Value.Int32 = 0;
+ tlsBaseGlobal.InitExpr.Opcode = WASM_OPCODE_I32_CONST;
+ tlsBaseGlobal.SymbolName = "__tls_base";
+ WasmSym::tlsBase =
+ symtab->addSyntheticGlobal("__tls_base", WASM_SYMBOL_VISIBILITY_HIDDEN,
+ make<InputGlobal>(tlsBaseGlobal, nullptr));
+
+ llvm::wasm::WasmGlobal tlsSizeGlobal;
+ tlsSizeGlobal.Type = {WASM_TYPE_I32, false};
+ tlsSizeGlobal.InitExpr.Value.Int32 = 0;
+ tlsSizeGlobal.InitExpr.Opcode = WASM_OPCODE_I32_CONST;
+ tlsSizeGlobal.SymbolName = "__tls_size";
+ WasmSym::tlsSize =
+ symtab->addSyntheticGlobal("__tls_size", WASM_SYMBOL_VISIBILITY_HIDDEN,
+ make<InputGlobal>(tlsSizeGlobal, nullptr));
+
+ WasmSym::initTLS = symtab->addSyntheticFunction(
+ "__wasm_init_tls", WASM_SYMBOL_VISIBILITY_HIDDEN,
+ make<SyntheticFunction>(i32ArgSignature, "__wasm_init_tls"));
+ }
+
WasmSym::dsoHandle = symtab->addSyntheticDataSymbol(
"__dso_handle", WASM_SYMBOL_VISIBILITY_HIDDEN);
}
Modified: lld/trunk/wasm/Symbols.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Symbols.cpp?rev=366272&r1=366271&r2=366272&view=diff
==============================================================================
--- lld/trunk/wasm/Symbols.cpp (original)
+++ lld/trunk/wasm/Symbols.cpp Tue Jul 16 15:00:45 2019
@@ -27,11 +27,14 @@ using namespace lld::wasm;
DefinedFunction *WasmSym::callCtors;
DefinedFunction *WasmSym::initMemory;
DefinedFunction *WasmSym::applyRelocs;
+DefinedFunction *WasmSym::initTLS;
DefinedData *WasmSym::dsoHandle;
DefinedData *WasmSym::dataEnd;
DefinedData *WasmSym::globalBase;
DefinedData *WasmSym::heapBase;
GlobalSymbol *WasmSym::stackPointer;
+GlobalSymbol *WasmSym::tlsBase;
+GlobalSymbol *WasmSym::tlsSize;
UndefinedGlobal *WasmSym::tableBase;
UndefinedGlobal *WasmSym::memoryBase;
@@ -200,8 +203,14 @@ DefinedFunction::DefinedFunction(StringR
uint32_t DefinedData::getVirtualAddress() const {
LLVM_DEBUG(dbgs() << "getVirtualAddress: " << getName() << "\n");
- if (segment)
+ if (segment) {
+ // For thread local data, the symbol location is relative to the start of
+ // the .tdata section, since they are used as offsets from __tls_base.
+ // Hence, we do not add in segment->outputSeg->startVA.
+ if (segment->outputSeg->name == ".tdata")
+ return segment->outputSegmentOffset + offset;
return segment->outputSeg->startVA + segment->outputSegmentOffset + offset;
+ }
return offset;
}
Modified: lld/trunk/wasm/Symbols.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Symbols.h?rev=366272&r1=366271&r2=366272&view=diff
==============================================================================
--- lld/trunk/wasm/Symbols.h (original)
+++ lld/trunk/wasm/Symbols.h Tue Jul 16 15:00:45 2019
@@ -426,6 +426,15 @@ struct WasmSym {
// linear memory.
static GlobalSymbol *stackPointer;
+ // __tls_base
+ // Global that holds the address of the base of the current thread's
+ // TLS block.
+ static GlobalSymbol *tlsBase;
+
+ // __tls_size
+ // Symbol whose value is the size of the TLS block.
+ static GlobalSymbol *tlsSize;
+
// __data_end
// Symbol marking the end of the data and bss.
static DefinedData *dataEnd;
@@ -448,6 +457,10 @@ struct WasmSym {
// Function that applies relocations to data segment post-instantiation.
static DefinedFunction *applyRelocs;
+ // __wasm_init_tls
+ // Function that allocates thread-local storage and initializes it.
+ static DefinedFunction *initTLS;
+
// __dso_handle
// Symbol used in calls to __cxa_atexit to determine current DLL
static DefinedData *dsoHandle;
Modified: lld/trunk/wasm/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Writer.cpp?rev=366272&r1=366271&r2=366272&view=diff
==============================================================================
--- lld/trunk/wasm/Writer.cpp (original)
+++ lld/trunk/wasm/Writer.cpp Tue Jul 16 15:00:45 2019
@@ -57,6 +57,7 @@ private:
void createInitMemoryFunction();
void createApplyRelocationsFunction();
void createCallCtorsFunction();
+ void createInitTLSFunction();
void assignIndexes();
void populateSymtab();
@@ -242,6 +243,11 @@ void Writer::layoutMemory() {
log(formatv("mem: {0,-15} offset={1,-8} size={2,-8} align={3}", seg->name,
memoryPtr, seg->size, seg->alignment));
memoryPtr += seg->size;
+
+ if (WasmSym::tlsSize && seg->name == ".tdata") {
+ auto *tlsSize = cast<DefinedGlobal>(WasmSym::tlsSize);
+ tlsSize->global->global.InitExpr.Value.Int32 = seg->size;
+ }
}
// TODO: Add .bss space here.
@@ -353,6 +359,7 @@ void Writer::populateTargetFeatures() {
StringMap<std::string> used;
StringMap<std::string> required;
StringMap<std::string> disallowed;
+ bool tlsUsed = false;
// Only infer used features if user did not specify features
bool inferFeatures = !config->features.hasValue();
@@ -385,6 +392,14 @@ void Writer::populateTargetFeatures() {
std::to_string(feature.Prefix));
}
}
+
+ for (InputSegment *segment : file->segments) {
+ if (!segment->live)
+ continue;
+ StringRef name = segment->getName();
+ if (name.startswith(".tdata") || name.startswith(".tbss"))
+ tlsUsed = true;
+ }
}
if (inferFeatures)
@@ -411,6 +426,10 @@ void Writer::populateTargetFeatures() {
error("'bulk-memory' feature must be used in order to emit passive "
"segments");
+ if (!used.count("bulk-memory") && tlsUsed)
+ error("'bulk-memory' feature must be used in order to use thread-local "
+ "storage");
+
// Validate that used features are allowed in output
if (!inferFeatures) {
for (auto &feature : used.keys()) {
@@ -492,8 +511,8 @@ void Writer::calculateExports() {
// implement in all major browsers.
// See: https://github.com/WebAssembly/mutable-global
if (g->getGlobalType()->Mutable) {
- // Only the __stack_pointer should ever be create as mutable.
- assert(g == WasmSym::stackPointer);
+ // Only __stack_pointer and __tls_base should ever be create as mutable.
+ assert(g == WasmSym::stackPointer || g == WasmSym::tlsBase);
continue;
}
export_ = {name, WASM_EXTERNAL_GLOBAL, g->getGlobalIndex()};
@@ -602,6 +621,11 @@ static StringRef getOutputDataSegmentNam
// we only have a single __memory_base to use as our base address.
if (config->isPic)
return ".data";
+ // We only support one thread-local segment, so we must merge the segments
+ // despite --no-merge-data-segments.
+ // We also need to merge .tbss into .tdata so they share the same offsets.
+ if (name.startswith(".tdata") || name.startswith(".tbss"))
+ return ".tdata";
if (!config->mergeDataSegments)
return name;
if (name.startswith(".text."))
@@ -625,7 +649,7 @@ void Writer::createOutputSegments() {
if (s == nullptr) {
LLVM_DEBUG(dbgs() << "new segment: " << name << "\n");
s = make<OutputSegment>(name, segments.size());
- if (config->passiveSegments)
+ if (config->passiveSegments || name == ".tdata")
s->initFlags = WASM_SEGMENT_IS_PASSIVE;
segments.push_back(s);
}
@@ -655,7 +679,7 @@ void Writer::createInitMemoryFunction()
// initialize passive data segments
for (const OutputSegment *s : segments) {
- if (s->initFlags & WASM_SEGMENT_IS_PASSIVE) {
+ if (s->initFlags & WASM_SEGMENT_IS_PASSIVE && s->name != ".tdata") {
// destination address
writeU8(os, WASM_OPCODE_I32_CONST, "i32.const");
writeSleb128(os, s->startVA, "destination address");
@@ -737,6 +761,49 @@ void Writer::createCallCtorsFunction() {
createFunction(WasmSym::callCtors, bodyContent);
}
+void Writer::createInitTLSFunction() {
+ if (!WasmSym::initTLS->isLive())
+ return;
+
+ std::string bodyContent;
+ {
+ raw_string_ostream os(bodyContent);
+
+ OutputSegment *tlsSeg = nullptr;
+ for (auto *seg : segments) {
+ if (seg->name == ".tdata")
+ tlsSeg = seg;
+ break;
+ }
+
+ writeUleb128(os, 0, "num locals");
+ if (tlsSeg) {
+ writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
+ writeUleb128(os, 0, "local index");
+
+ writeU8(os, WASM_OPCODE_GLOBAL_SET, "global.set");
+ writeUleb128(os, WasmSym::tlsBase->getGlobalIndex(), "global index");
+
+ writeU8(os, WASM_OPCODE_LOCAL_GET, "local.get");
+ writeUleb128(os, 0, "local index");
+
+ writeU8(os, WASM_OPCODE_I32_CONST, "i32.const");
+ writeSleb128(os, 0, "segment offset");
+
+ writeU8(os, WASM_OPCODE_I32_CONST, "i32.const");
+ writeSleb128(os, tlsSeg->size, "memory region size");
+
+ writeU8(os, WASM_OPCODE_MISC_PREFIX, "bulk-memory prefix");
+ writeUleb128(os, WASM_OPCODE_MEMORY_INIT, "MEMORY.INIT");
+ writeUleb128(os, tlsSeg->index, "segment index immediate");
+ writeU8(os, 0, "memory index immediate");
+ }
+ writeU8(os, WASM_OPCODE_END, "end function");
+ }
+
+ createFunction(WasmSym::initTLS, bodyContent);
+}
+
// Populate InitFunctions vector with init functions from all input objects.
// This is then used either when creating the output linking section or to
// synthesize the "__wasm_call_ctors" function.
@@ -829,6 +896,12 @@ void Writer::run() {
createCallCtorsFunction();
}
+ if (config->sharedMemory && !config->shared)
+ createInitTLSFunction();
+
+ if (errorCount())
+ return;
+
log("-- calculateTypes");
calculateTypes();
log("-- calculateExports");
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