src/wasm/wasm-constants.h

// Copyright 2015 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#if !V8_ENABLE_WEBASSEMBLY
#error This header should only be included if WebAssembly is enabled.
#endif  // !V8_ENABLE_WEBASSEMBLY

#ifndef V8_WASM_WASM_CONSTANTS_H_
#define V8_WASM_WASM_CONSTANTS_H_

#include <cstddef>
#include <cstdint>

#include "src/common/globals.h"

namespace v8 {
namespace internal {
namespace wasm {

// Binary encoding of the module header.
constexpr uint32_t kWasmMagic = 0x6d736100;
constexpr uint32_t kWasmVersion = 0x01;

// Binary encoding of value and heap types.
enum ValueTypeCode : uint8_t {
  // Current value types
  kVoidCode = 0x40,
  kI32Code = 0x7f,              // -0x01
  kI64Code = 0x7e,              // -0x02
  kF32Code = 0x7d,              // -0x03
  kF64Code = 0x7c,              // -0x04
  kS128Code = 0x7b,             // -0x05
  kI8Code = 0x78,               // -0x08, packed type
  kI16Code = 0x77,              // -0x09, packed type
  kNoExnCode = 0x74,            // -0x0c
  kNoFuncCode = 0x73,           // -0x0d
  kNoExternCode = 0x72,         // -0x0e
  kNoneCode = 0x71,             // -0x0f
  kFuncRefCode = 0x70,          // -0x10
  kExternRefCode = 0x6f,        // -0x11
  kAnyRefCode = 0x6e,           // -0x12
  kEqRefCode = 0x6d,            // -0x13
  kI31RefCode = 0x6c,           // -0x14
  kStructRefCode = 0x6b,        // -0x15
  kArrayRefCode = 0x6a,         // -0x16
  kRefCode = 0x64,              // -0x1c
  kRefNullCode = 0x63,          // -0x1d
                                // Non-finalized proposals below.
  kExnRefCode = 0x69,           // -0x17
  kStringRefCode = 0x67,        // -0x19
  kStringViewWtf8Code = 0x66,   // -0x1a
  kStringViewWtf16Code = 0x62,  // -0x1e
  kStringViewIterCode = 0x61,   // -0x1f
};

// Binary encoding of type definitions.
constexpr uint8_t kSharedFlagCode = 0x65;
constexpr uint8_t kWasmFunctionTypeCode = 0x60;
constexpr uint8_t kWasmStructTypeCode = 0x5f;
constexpr uint8_t kWasmArrayTypeCode = 0x5e;
constexpr uint8_t kWasmSubtypeCode = 0x50;
constexpr uint8_t kWasmSubtypeFinalCode = 0x4f;
constexpr uint8_t kWasmRecursiveTypeGroupCode = 0x4e;

// Binary encoding of import/export kinds.
enum ImportExportKindCode : uint8_t {
  kExternalFunction = 0,
  kExternalTable = 1,
  kExternalMemory = 2,
  kExternalGlobal = 3,
  kExternalTag = 4
};

enum LimitsFlags : uint8_t {
  kNoMaximum = 0x00,                 // Also valid for table limits.
  kWithMaximum = 0x01,               // Also valid for table limits.
  kSharedNoMaximum = 0x02,           // Only valid for memory limits.
  kSharedWithMaximum = 0x03,         // Only valid for memory limits.
  kMemory64NoMaximum = 0x04,         // Only valid for memory limits.
  kMemory64WithMaximum = 0x05,       // Only valid for memory limits.
  kMemory64SharedNoMaximum = 0x06,   // Only valid for memory limits.
  kMemory64SharedWithMaximum = 0x07  // Only valid for memory limits.
};

// Flags for data and element segments.
enum SegmentFlags : uint8_t {
  kActiveNoIndex = 0,    // Active segment with a memory/table index of zero.
  kPassive = 1,          // Passive segment.
  kActiveWithIndex = 2,  // Active segment with a given memory/table index.
};

// Binary encoding of sections identifiers.
enum SectionCode : int8_t {
  kUnknownSectionCode = 0,     // code for unknown sections
  kTypeSectionCode = 1,        // Function signature declarations
  kImportSectionCode = 2,      // Import declarations
  kFunctionSectionCode = 3,    // Function declarations
  kTableSectionCode = 4,       // Indirect function table and others
  kMemorySectionCode = 5,      // Memory attributes
  kGlobalSectionCode = 6,      // Global declarations
  kExportSectionCode = 7,      // Exports
  kStartSectionCode = 8,       // Start function declaration
  kElementSectionCode = 9,     // Elements section
  kCodeSectionCode = 10,       // Function code
  kDataSectionCode = 11,       // Data segments
  kDataCountSectionCode = 12,  // Number of data segments
  kTagSectionCode = 13,        // Tag section
  kStringRefSectionCode = 14,  // Stringref literal section

  // The following sections are custom sections, and are identified using a
  // string rather than an integer. Their enumeration values are not guaranteed
  // to be consistent.
  kNameSectionCode,               // Name section (encoded as a string)
  kSourceMappingURLSectionCode,   // Source Map URL section
  kDebugInfoSectionCode,          // DWARF section .debug_info
  kExternalDebugInfoSectionCode,  // Section encoding the external symbol path
  kInstTraceSectionCode,          // Instruction trace section
  kCompilationHintsSectionCode,   // Compilation hints section
  kBranchHintsSectionCode,        // Branch hints section

  // Helper values
  kFirstSectionInModule = kTypeSectionCode,
  kLastKnownModuleSection = kStringRefSectionCode,
  kFirstUnorderedSection = kDataCountSectionCode,
};

// Binary encoding of compilation hints.
constexpr uint8_t kDefaultCompilationHint = 0x0;
constexpr uint8_t kNoCompilationHint = kMaxUInt8;

// Binary encoding of name section kinds.
enum NameSectionKindCode : uint8_t {
  kModuleCode = 0,
  kFunctionCode = 1,
  kLocalCode = 2,
  // https://github.com/WebAssembly/extended-name-section/
  kLabelCode = 3,
  kTypeCode = 4,
  kTableCode = 5,
  kMemoryCode = 6,
  kGlobalCode = 7,
  kElementSegmentCode = 8,
  kDataSegmentCode = 9,
  // https://github.com/WebAssembly/gc/issues/193
  kFieldCode = 10,
  // https://github.com/WebAssembly/exception-handling/pull/213
  kTagCode = 11,
};

enum CatchKind : uint8_t {
  kCatch = 0x0,
  kCatchRef = 0x1,
  kCatchAll = 0x2,
  kCatchAllRef = 0x3,
  kLastCatchKind = kCatchAllRef,
};

constexpr char kMagicStringConstantsModuleName = '\'';

constexpr size_t kWasmPageSize = 0x10000;
constexpr uint32_t kWasmPageSizeLog2 = 16;
static_assert(kWasmPageSize == size_t{1} << kWasmPageSizeLog2, "consistency");

// TODO(wasm): Wrap WasmCodePosition in a struct.
using WasmCodePosition = int;
constexpr WasmCodePosition kNoCodePosition = -1;

constexpr uint32_t kExceptionAttribute = 0;

constexpr int kAnonymousFuncIndex = -1;

// The number of calls to an exported Wasm function that will be handled
// by the generic wrapper. Once the budget is exhausted, a specific wrapper
// is to be compiled for the function's signature.
// The abstract goal of the tiering strategy for the js-to-wasm wrappers is to
// use the generic wrapper as much as possible (less space, no need to compile),
// but fall back to compiling a specific wrapper for any function (signature)
// that is used often enough for the generic wrapper's small execution penalty
// to start adding up.
// So, when choosing a value for the initial budget, we are interested in a
// value that skips on tiering up functions that are called only a few times and
// the tier-up only wastes resources, but triggers compilation of specific
// wrappers early on for those functions that have the potential to be called
// often enough.
constexpr uint32_t kGenericWrapperBudget = 1000;

// The minimum length of supertype arrays for wasm-gc types. Having a size > 0
// gives up some module size for faster access to the supertypes.
constexpr uint32_t kMinimumSupertypeArraySize = 3;

// Maximum number of call targets tracked per call.
constexpr int kMaxPolymorphism = 4;

// A struct field beyond this limit needs an explicit null check (trapping null
// access not guaranteed to behave properly).
constexpr int kMaxStructFieldIndexForImplicitNullCheck = 4000;

#if V8_TARGET_ARCH_X64
constexpr int32_t kOSRTargetOffset = 4 * kSystemPointerSize;
#endif

enum FPRelativeScope {
  kEnterFPRelativeOnlyScope,
  kLeaveFPRelativeOnlyScope,
};

}  // namespace wasm
}  // namespace internal
}  // namespace v8

#endif  // V8_WASM_WASM_CONSTANTS_H_