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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ *
+ * Copyright 2019 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef wasm_gc_h
+#define wasm_gc_h
+
+#include "mozilla/BinarySearch.h"
+
+#include "jit/ABIArgGenerator.h" // For ABIArgIter
+#include "js/AllocPolicy.h"
+#include "js/Vector.h"
+#include "util/Memory.h"
+#include "wasm/WasmBuiltins.h"
+#include "wasm/WasmFrame.h"
+#include "wasm/WasmSerialize.h"
+
+namespace js {
+
+namespace jit {
+class Label;
+class MacroAssembler;
+} // namespace jit
+
+namespace wasm {
+
+class ArgTypeVector;
+class BytecodeOffset;
+
+using jit::Label;
+using jit::MIRType;
+using jit::Register;
+
+// Definitions for stackmaps.
+
+using ExitStubMapVector = Vector<bool, 32, SystemAllocPolicy>;
+
+struct StackMapHeader {
+ explicit StackMapHeader(uint32_t numMappedWords = 0)
+ : numMappedWords(numMappedWords),
+ numExitStubWords(0),
+ frameOffsetFromTop(0),
+ hasDebugFrameWithLiveRefs(0) {}
+
+ // The total number of stack words covered by the map ..
+ static constexpr size_t MappedWordsBits = 30;
+ uint32_t numMappedWords : MappedWordsBits;
+
+ // .. of which this many are "exit stub" extras
+ static constexpr size_t ExitStubWordsBits = 6;
+ uint32_t numExitStubWords : ExitStubWordsBits;
+
+ // Where is Frame* relative to the top? This is an offset in words. On every
+ // platform, FrameOffsetBits needs to be at least
+ // ceil(log2(MaxParams*sizeof-biggest-param-type-in-words)). The most
+ // constraining platforms are 32-bit with SIMD support, currently x86-32.
+ static constexpr size_t FrameOffsetBits = 12;
+ uint32_t frameOffsetFromTop : FrameOffsetBits;
+
+ // Notes the presence of a DebugFrame with possibly-live references. A
+ // DebugFrame may or may not contain GC-managed data; in situations when it is
+ // possible that any pointers in the DebugFrame are non-null, the DebugFrame
+ // gets a stackmap.
+ uint32_t hasDebugFrameWithLiveRefs : 1;
+
+ WASM_CHECK_CACHEABLE_POD(numMappedWords, numExitStubWords, frameOffsetFromTop,
+ hasDebugFrameWithLiveRefs);
+
+ static constexpr uint32_t maxMappedWords = (1 << MappedWordsBits) - 1;
+ static constexpr uint32_t maxExitStubWords = (1 << ExitStubWordsBits) - 1;
+ static constexpr uint32_t maxFrameOffsetFromTop = (1 << FrameOffsetBits) - 1;
+
+ static constexpr size_t MaxParamSize =
+ std::max(sizeof(jit::FloatRegisters::RegisterContent),
+ sizeof(jit::Registers::RegisterContent));
+
+ // Add 16 words to account for the size of FrameWithInstances including any
+ // shadow stack (at worst 8 words total), and then a little headroom in case
+ // the argument area had to be aligned.
+ static_assert(FrameWithInstances::sizeOf() / sizeof(void*) <= 8);
+ static_assert(maxFrameOffsetFromTop >=
+ (MaxParams * MaxParamSize / sizeof(void*)) + 16,
+ "limited size of the offset field");
+};
+
+WASM_DECLARE_CACHEABLE_POD(StackMapHeader);
+
+// This is the expected size for the header
+static_assert(sizeof(StackMapHeader) == 8,
+ "wasm::StackMapHeader has unexpected size");
+
+// A StackMap is a bit-array containing numMappedWords bits, one bit per
+// word of stack. Bit index zero is for the lowest addressed word in the
+// range.
+//
+// This is a variable-length structure whose size must be known at creation
+// time.
+//
+// Users of the map will know the address of the wasm::Frame that is covered
+// by this map. In order that they can calculate the exact address range
+// covered by the map, the map also stores the offset, from the highest
+// addressed word of the map, of the embedded wasm::Frame. This is an offset
+// down from the highest address, rather than up from the lowest, so as to
+// limit its range to FrameOffsetBits bits.
+//
+// The stackmap may also cover a DebugFrame (all DebugFrames which may
+// potentially contain live pointers into the JS heap get a map). If so that
+// can be noted, since users of the map need to trace pointers in a
+// DebugFrame.
+//
+// Finally, for sanity checking only, for stackmaps associated with a wasm
+// trap exit stub, the number of words used by the trap exit stub save area
+// is also noted. This is used in Instance::traceFrame to check that the
+// TrapExitDummyValue is in the expected place in the frame.
+struct StackMap final {
+ // The header contains the constant-sized fields before the variable-sized
+ // bitmap that follows.
+ StackMapHeader header;
+
+ private:
+ // The variable-sized bitmap.
+ uint32_t bitmap[1];
+
+ explicit StackMap(uint32_t numMappedWords) : header(numMappedWords) {
+ const uint32_t nBitmap = calcNBitmap(header.numMappedWords);
+ memset(bitmap, 0, nBitmap * sizeof(bitmap[0]));
+ }
+ explicit StackMap(const StackMapHeader& header) : header(header) {
+ const uint32_t nBitmap = calcNBitmap(header.numMappedWords);
+ memset(bitmap, 0, nBitmap * sizeof(bitmap[0]));
+ }
+
+ public:
+ static StackMap* create(uint32_t numMappedWords) {
+ size_t size = allocationSizeInBytes(numMappedWords);
+ char* buf = (char*)js_malloc(size);
+ if (!buf) {
+ return nullptr;
+ }
+ return ::new (buf) StackMap(numMappedWords);
+ }
+ static StackMap* create(const StackMapHeader& header) {
+ size_t size = allocationSizeInBytes(header.numMappedWords);
+ char* buf = (char*)js_malloc(size);
+ if (!buf) {
+ return nullptr;
+ }
+ return ::new (buf) StackMap(header);
+ }
+
+ void destroy() { js_free((char*)this); }
+
+ // Returns the size of a `StackMap` allocated with `numMappedWords`.
+ static size_t allocationSizeInBytes(uint32_t numMappedWords) {
+ uint32_t nBitmap = calcNBitmap(numMappedWords);
+ return sizeof(StackMap) + (nBitmap - 1) * sizeof(bitmap[0]);
+ }
+
+ // Returns the allocated size of this `StackMap`.
+ size_t allocationSizeInBytes() const {
+ return allocationSizeInBytes(header.numMappedWords);
+ }
+
+ // Record the number of words in the map used as a wasm trap exit stub
+ // save area. See comment above.
+ void setExitStubWords(uint32_t nWords) {
+ MOZ_ASSERT(header.numExitStubWords == 0);
+ MOZ_RELEASE_ASSERT(nWords <= header.maxExitStubWords);
+ MOZ_ASSERT(nWords <= header.numMappedWords);
+ header.numExitStubWords = nWords;
+ }
+
+ // Record the offset from the highest-addressed word of the map, that the
+ // wasm::Frame lives at. See comment above.
+ void setFrameOffsetFromTop(uint32_t nWords) {
+ MOZ_ASSERT(header.frameOffsetFromTop == 0);
+ MOZ_RELEASE_ASSERT(nWords <= StackMapHeader::maxFrameOffsetFromTop);
+ MOZ_ASSERT(header.frameOffsetFromTop < header.numMappedWords);
+ header.frameOffsetFromTop = nWords;
+ }
+
+ // If the frame described by this StackMap includes a DebugFrame, call here to
+ // record that fact.
+ void setHasDebugFrameWithLiveRefs() {
+ MOZ_ASSERT(header.hasDebugFrameWithLiveRefs == 0);
+ header.hasDebugFrameWithLiveRefs = 1;
+ }
+
+ inline void setBit(uint32_t bitIndex) {
+ MOZ_ASSERT(bitIndex < header.numMappedWords);
+ uint32_t wordIndex = bitIndex / wordsPerBitmapElem;
+ uint32_t wordOffset = bitIndex % wordsPerBitmapElem;
+ bitmap[wordIndex] |= (1 << wordOffset);
+ }
+
+ inline uint32_t getBit(uint32_t bitIndex) const {
+ MOZ_ASSERT(bitIndex < header.numMappedWords);
+ uint32_t wordIndex = bitIndex / wordsPerBitmapElem;
+ uint32_t wordOffset = bitIndex % wordsPerBitmapElem;
+ return (bitmap[wordIndex] >> wordOffset) & 1;
+ }
+
+ inline uint8_t* rawBitmap() { return (uint8_t*)&bitmap; }
+ inline const uint8_t* rawBitmap() const { return (const uint8_t*)&bitmap; }
+ inline size_t rawBitmapLengthInBytes() const {
+ return calcNBitmap(header.numMappedWords) * sizeof(uint32_t);
+ }
+
+ private:
+ static constexpr uint32_t wordsPerBitmapElem = sizeof(bitmap[0]) * 8;
+
+ static uint32_t calcNBitmap(uint32_t numMappedWords) {
+ MOZ_RELEASE_ASSERT(numMappedWords <= StackMapHeader::maxMappedWords);
+ uint32_t nBitmap =
+ (numMappedWords + wordsPerBitmapElem - 1) / wordsPerBitmapElem;
+ return nBitmap == 0 ? 1 : nBitmap;
+ }
+};
+
+// This is the expected size for a map that covers 32 or fewer words.
+static_assert(sizeof(StackMap) == 12, "wasm::StackMap has unexpected size");
+
+class StackMaps {
+ public:
+ // A Maplet holds a single code-address-to-map binding. Note that the
+ // code address is the lowest address of the instruction immediately
+ // following the instruction of interest, not of the instruction of
+ // interest itself. In practice (at least for the Wasm Baseline compiler)
+ // this means that |nextInsnAddr| points either immediately after a call
+ // instruction, after a trap instruction or after a no-op.
+ struct Maplet {
+ const uint8_t* nextInsnAddr;
+ StackMap* map;
+ Maplet(const uint8_t* nextInsnAddr, StackMap* map)
+ : nextInsnAddr(nextInsnAddr), map(map) {}
+ void offsetBy(uintptr_t delta) { nextInsnAddr += delta; }
+ bool operator<(const Maplet& other) const {
+ return uintptr_t(nextInsnAddr) < uintptr_t(other.nextInsnAddr);
+ }
+ };
+
+ private:
+ bool sorted_;
+ Vector<Maplet, 0, SystemAllocPolicy> mapping_;
+
+ public:
+ StackMaps() : sorted_(false) {}
+ ~StackMaps() {
+ for (auto& maplet : mapping_) {
+ maplet.map->destroy();
+ maplet.map = nullptr;
+ }
+ }
+ [[nodiscard]] bool add(const uint8_t* nextInsnAddr, StackMap* map) {
+ MOZ_ASSERT(!sorted_);
+ return mapping_.append(Maplet(nextInsnAddr, map));
+ }
+ [[nodiscard]] bool add(const Maplet& maplet) {
+ return add(maplet.nextInsnAddr, maplet.map);
+ }
+ void clear() {
+ for (auto& maplet : mapping_) {
+ maplet.nextInsnAddr = nullptr;
+ maplet.map = nullptr;
+ }
+ mapping_.clear();
+ }
+ bool empty() const { return mapping_.empty(); }
+ size_t length() const { return mapping_.length(); }
+ Maplet* getRef(size_t i) { return &mapping_[i]; }
+ Maplet get(size_t i) const { return mapping_[i]; }
+ Maplet move(size_t i) {
+ Maplet m = mapping_[i];
+ mapping_[i].map = nullptr;
+ return m;
+ }
+ void offsetBy(uintptr_t delta) {
+ for (auto& maplet : mapping_) maplet.offsetBy(delta);
+ }
+ void finishAndSort() {
+ MOZ_ASSERT(!sorted_);
+ std::sort(mapping_.begin(), mapping_.end());
+ sorted_ = true;
+ }
+ void finishAlreadySorted() {
+ MOZ_ASSERT(!sorted_);
+ MOZ_ASSERT(std::is_sorted(mapping_.begin(), mapping_.end()));
+ sorted_ = true;
+ }
+ const StackMap* findMap(const uint8_t* nextInsnAddr) const {
+ struct Comparator {
+ int operator()(Maplet aVal) const {
+ if (uintptr_t(mTarget) < uintptr_t(aVal.nextInsnAddr)) {
+ return -1;
+ }
+ if (uintptr_t(mTarget) > uintptr_t(aVal.nextInsnAddr)) {
+ return 1;
+ }
+ return 0;
+ }
+ explicit Comparator(const uint8_t* aTarget) : mTarget(aTarget) {}
+ const uint8_t* mTarget;
+ };
+
+ size_t result;
+ if (mozilla::BinarySearchIf(mapping_, 0, mapping_.length(),
+ Comparator(nextInsnAddr), &result)) {
+ return mapping_[result].map;
+ }
+
+ return nullptr;
+ }
+};
+
+// Supporting code for creation of stackmaps.
+
+// StackArgAreaSizeUnaligned returns the size, in bytes, of the stack arg area
+// size needed to pass |argTypes|, excluding any alignment padding beyond the
+// size of the area as a whole. The size is as determined by the platforms
+// native ABI.
+//
+// StackArgAreaSizeAligned returns the same, but rounded up to the nearest 16
+// byte boundary.
+//
+// Note, StackArgAreaSize{Unaligned,Aligned}() must process all the arguments
+// in order to take into account all necessary alignment constraints. The
+// signature must include any receiver argument -- in other words, it must be
+// the complete native-ABI-level call signature.
+template <class T>
+static inline size_t StackArgAreaSizeUnaligned(const T& argTypes) {
+ jit::WasmABIArgIter<const T> i(argTypes);
+ while (!i.done()) {
+ i++;
+ }
+ return i.stackBytesConsumedSoFar();
+}
+
+static inline size_t StackArgAreaSizeUnaligned(
+ const SymbolicAddressSignature& saSig) {
+ // WasmABIArgIter::ABIArgIter wants the items to be iterated over to be
+ // presented in some type that has methods length() and operator[]. So we
+ // have to wrap up |saSig|'s array of types in this API-matching class.
+ class MOZ_STACK_CLASS ItemsAndLength {
+ const MIRType* items_;
+ size_t length_;
+
+ public:
+ ItemsAndLength(const MIRType* items, size_t length)
+ : items_(items), length_(length) {}
+ size_t length() const { return length_; }
+ MIRType operator[](size_t i) const { return items_[i]; }
+ };
+
+ // Assert, at least crudely, that we're not accidentally going to run off
+ // the end of the array of types, nor into undefined parts of it, while
+ // iterating.
+ MOZ_ASSERT(saSig.numArgs <
+ sizeof(saSig.argTypes) / sizeof(saSig.argTypes[0]));
+ MOZ_ASSERT(saSig.argTypes[saSig.numArgs] == MIRType::None /*the end marker*/);
+
+ ItemsAndLength itemsAndLength(saSig.argTypes, saSig.numArgs);
+ return StackArgAreaSizeUnaligned(itemsAndLength);
+}
+
+static inline size_t AlignStackArgAreaSize(size_t unalignedSize) {
+ return AlignBytes(unalignedSize, jit::WasmStackAlignment);
+}
+
+// A stackmap creation helper. Create a stackmap from a vector of booleans.
+// The caller owns the resulting stackmap.
+
+using StackMapBoolVector = Vector<bool, 128, SystemAllocPolicy>;
+
+wasm::StackMap* ConvertStackMapBoolVectorToStackMap(
+ const StackMapBoolVector& vec, bool hasRefs);
+
+// Generate a stackmap for a function's stack-overflow-at-entry trap, with
+// the structure:
+//
+// <reg dump area>
+// | ++ <space reserved before trap, if any>
+// | ++ <space for Frame>
+// | ++ <inbound arg area>
+// | |
+// Lowest Addr Highest Addr
+//
+// The caller owns the resulting stackmap. This assumes a grow-down stack.
+//
+// For non-debug builds, if the stackmap would contain no pointers, no
+// stackmap is created, and nullptr is returned. For a debug build, a
+// stackmap is always created and returned.
+//
+// The "space reserved before trap" is the space reserved by
+// MacroAssembler::wasmReserveStackChecked, in the case where the frame is
+// "small", as determined by that function.
+[[nodiscard]] bool CreateStackMapForFunctionEntryTrap(
+ const ArgTypeVector& argTypes, const jit::RegisterOffsets& trapExitLayout,
+ size_t trapExitLayoutWords, size_t nBytesReservedBeforeTrap,
+ size_t nInboundStackArgBytes, wasm::StackMap** result);
+
+// At a resumable wasm trap, the machine's registers are saved on the stack by
+// (code generated by) GenerateTrapExit(). This function writes into |args| a
+// vector of booleans describing the ref-ness of the saved integer registers.
+// |args[0]| corresponds to the low addressed end of the described section of
+// the save area.
+[[nodiscard]] bool GenerateStackmapEntriesForTrapExit(
+ const ArgTypeVector& args, const jit::RegisterOffsets& trapExitLayout,
+ const size_t trapExitLayoutNumWords, ExitStubMapVector* extras);
+
+// Shared write barrier code.
+//
+// A barriered store looks like this:
+//
+// Label skipPreBarrier;
+// EmitWasmPreBarrierGuard(..., &skipPreBarrier);
+// <COMPILER-SPECIFIC ACTIONS HERE>
+// EmitWasmPreBarrierCall(...);
+// bind(&skipPreBarrier);
+//
+// <STORE THE VALUE IN MEMORY HERE>
+//
+// Label skipPostBarrier;
+// <COMPILER-SPECIFIC ACTIONS HERE>
+// EmitWasmPostBarrierGuard(..., &skipPostBarrier);
+// <CALL POST-BARRIER HERE IN A COMPILER-SPECIFIC WAY>
+// bind(&skipPostBarrier);
+//
+// The actions are divided up to allow other actions to be placed between them,
+// such as saving and restoring live registers. The postbarrier call invokes
+// C++ and will kill all live registers.
+
+// Before storing a GC pointer value in memory, skip to `skipBarrier` if the
+// prebarrier is not needed. Will clobber `scratch`.
+//
+// It is OK for `instance` and `scratch` to be the same register.
+//
+// If `trapOffset` is non-null, then metadata to catch a null access and emit
+// a null pointer exception will be emitted. This will only catch a null access
+// due to an incremental GC being in progress, the write that follows this
+// pre-barrier guard must also be guarded against null.
+
+void EmitWasmPreBarrierGuard(jit::MacroAssembler& masm, Register instance,
+ Register scratch, Register valueAddr,
+ size_t valueOffset, Label* skipBarrier,
+ BytecodeOffset* trapOffset);
+
+// Before storing a GC pointer value in memory, call out-of-line prebarrier
+// code. This assumes `PreBarrierReg` contains the address that will be updated.
+// On ARM64 it also assums that x28 (the PseudoStackPointer) has the same value
+// as SP. `PreBarrierReg` is preserved by the barrier function. Will clobber
+// `scratch`.
+//
+// It is OK for `instance` and `scratch` to be the same register.
+
+void EmitWasmPreBarrierCall(jit::MacroAssembler& masm, Register instance,
+ Register scratch, Register valueAddr,
+ size_t valueOffset);
+
+// After storing a GC pointer value in memory, skip to `skipBarrier` if a
+// postbarrier is not needed. If the location being set is in an heap-allocated
+// object then `object` must reference that object; otherwise it should be None.
+// The value that was stored is `setValue`. Will clobber `otherScratch` and
+// will use other available scratch registers.
+//
+// `otherScratch` cannot be a designated scratch register.
+
+void EmitWasmPostBarrierGuard(jit::MacroAssembler& masm,
+ const mozilla::Maybe<Register>& object,
+ Register otherScratch, Register setValue,
+ Label* skipBarrier);
+
+#ifdef DEBUG
+// Check whether |nextPC| is a valid code address for a stackmap created by
+// this compiler.
+bool IsValidStackMapKey(bool debugEnabled, const uint8_t* nextPC);
+#endif
+
+} // namespace wasm
+} // namespace js
+
+#endif // wasm_gc_h
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