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// Copyright 2006-2008 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.
#ifndef V8_FLAGS_FLAGS_H_
#define V8_FLAGS_FLAGS_H_
#include "src/base/optional.h"
#include "src/common/globals.h"
#if V8_ENABLE_WEBASSEMBLY
// Include the wasm-limits.h header for some default values of Wasm flags.
// This can be reverted once we can use designated initializations (C++20) for
// {v8_flags} (defined in flags.cc) instead of specifying the default values in
// the header and using the default constructor.
#include "src/wasm/wasm-limits.h"
#endif
namespace v8::internal {
// The value of a single flag (this is the type of all v8_flags.* fields).
template <typename T>
class FlagValue {
// {FlagValue} types will be memory-protected in {FlagList::FreezeFlags}.
// We currently allow the following types to be used for flags:
// - Arithmetic types like bool, int, size_t, double; those will trivially be
// protected.
// - base::Optional<bool>, which is basically a POD, and can also be
// protected.
// - const char*, for which we currently do not protect the actual string
// value. TODO(12887): Also protect the string storage.
//
// Other types can be added as needed, after checking that memory protection
// works for them.
static_assert(std::is_same_v<std::decay_t<T>, T>);
static_assert(std::is_arithmetic_v<T> ||
std::is_same_v<base::Optional<bool>, T> ||
std::is_same_v<const char*, T>);
public:
explicit constexpr FlagValue(T value) : value_(value) {}
// Implicitly convert to a {T}. Not marked {constexpr} so we do not get
// compiler warnings about dead code (when checking readonly flags).
operator T() const { return value_; }
// Explicitly convert to a {T} via {value()}. This is {constexpr} so we can
// use it for computing other constants.
constexpr T value() const { return value_; }
// Assign a new value (defined below).
inline FlagValue<T>& operator=(T new_value);
private:
T value_;
};
// Declare a struct to hold all of our flags.
struct alignas(kMinimumOSPageSize) FlagValues {
FlagValues() = default;
// No copying, moving, or assigning. This is a singleton struct.
FlagValues(const FlagValues&) = delete;
FlagValues(FlagValues&&) = delete;
FlagValues& operator=(const FlagValues&) = delete;
FlagValues& operator=(FlagValues&&) = delete;
#define FLAG_MODE_DECLARE
#include "src/flags/flag-definitions.h" // NOLINT(build/include)
#undef FLAG_MODE_DECLARE
};
V8_EXPORT_PRIVATE extern FlagValues v8_flags;
// The global list of all flags.
class V8_EXPORT_PRIVATE FlagList {
public:
class HelpOptions {
public:
enum ExitBehavior : bool { kExit = true, kDontExit = false };
explicit HelpOptions(ExitBehavior exit_behavior = kExit,
const char* usage = nullptr)
: exit_behavior_(exit_behavior), usage_(usage) {}
bool ShouldExit() { return exit_behavior_ == kExit; }
bool HasUsage() { return usage_ != nullptr; }
const char* usage() { return usage_; }
private:
ExitBehavior exit_behavior_;
const char* usage_;
};
// Set the flag values by parsing the command line. If remove_flags is
// set, the recognized flags and associated values are removed from (argc,
// argv) and only unknown arguments remain. Returns 0 if no error occurred.
// Otherwise, returns the argv index > 0 for the argument where an error
// occurred. In that case, (argc, argv) will remain unchanged independent of
// the remove_flags value, and no assumptions about flag settings should be
// made. If exit_behavior is set to Exit and --help has been specified on the
// command line, then the usage string will be printed, if it was specified,
// followed by the help flag and then the process will exit. Otherwise the
// flag help will be displayed but execution will continue.
//
// The following syntax for flags is accepted (both '-' and '--' are ok):
//
// --flag (bool flags only)
// --no-flag (bool flags only)
// --flag=value (non-bool flags only, no spaces around '=')
// --flag value (non-bool flags only)
// -- (capture all remaining args in JavaScript)
static int SetFlagsFromCommandLine(
int* argc, char** argv, bool remove_flags,
FlagList::HelpOptions help_options = FlagList::HelpOptions());
// Set the flag values by parsing the string str. Splits string into argc
// substrings argv[], each of which consisting of non-white-space chars,
// and then calls SetFlagsFromCommandLine() and returns its result.
static int SetFlagsFromString(const char* str, size_t len);
// Freeze the current flag values (disallow changes via the API).
static void FreezeFlags();
// Returns true if the flags are currently frozen.
static bool IsFrozen();
// Free dynamically allocated memory of strings. This is called during
// teardown; flag values cannot be used afterwards any more.
static void ReleaseDynamicAllocations();
// Print help to stdout with flags, types, and default values.
static void PrintHelp();
static void PrintValues();
// Set flags as consequence of being implied by another flag.
static void EnforceFlagImplications();
// Hash of flags (to quickly determine mismatching flag expectations).
// This hash is calculated during V8::Initialize and cached.
static uint32_t Hash();
private:
// Reset the flag hash on flag changes. This is a private method called from
// {FlagValue<T>::operator=}; there should be no need to call it from any
// other place.
static void ResetFlagHash();
// Make {FlagValue<T>} a friend, so it can call {ResetFlagHash()}.
template <typename T>
friend class FlagValue;
};
template <typename T>
FlagValue<T>& FlagValue<T>::operator=(T new_value) {
if (new_value != value_) {
FlagList::ResetFlagHash();
value_ = new_value;
}
return *this;
}
} // namespace v8::internal
#endif // V8_FLAGS_FLAGS_H_
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