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54cb9c77d9
Summary: The following are risks associated with pointer-to-pointer reinterpret_cast: * Can produce the "wrong result" (crash or memory corruption). IIRC, in theory this can happen for any up-cast or down-cast for a non-standard-layout type, though in practice would only happen for multiple inheritance cases (where the base class pointer might be "inside" the derived object). We don't use multiple inheritance a lot, but we do. * Can mask useful compiler errors upon code change, including converting between unrelated pointer types that you are expecting to be related, and converting between pointer and scalar types unintentionally. I can only think of some obscure cases where static_cast could be troublesome when it compiles as a replacement: * Going through `void*` could plausibly cause unnecessary or broken pointer arithmetic. Suppose we have `struct Derived: public Base1, public Base2`. If we have `Derived*` -> `void*` -> `Base2*` -> `Derived*` through reinterpret casts, this could plausibly work (though technical UB) assuming the `Base2*` is not dereferenced. Changing to static cast could introduce breaking pointer arithmetic. * Unnecessary (but safe) pointer arithmetic could arise in a case like `Derived*` -> `Base2*` -> `Derived*` where before the Base2 pointer might not have been dereferenced. This could potentially affect performance. With some light scripting, I tried replacing pointer-to-pointer reinterpret_casts with static_cast and kept the cases that still compile. Most occurrences of reinterpret_cast have successfully been changed (except for java/ and third-party/). 294 changed, 257 remain. A couple of related interventions included here: * Previously Cache::Handle was not actually derived from in the implementations and just used as a `void*` stand-in with reinterpret_cast. Now there is a relationship to allow static_cast. In theory, this could introduce pointer arithmetic (as described above) but is unlikely without multiple inheritance AND non-empty Cache::Handle. * Remove some unnecessary casts to void* as this is allowed to be implicit (for better or worse). Most of the remaining reinterpret_casts are for converting to/from raw bytes of objects. We could consider better idioms for these patterns in follow-up work. I wish there were a way to implement a template variant of static_cast that would only compile if no pointer arithmetic is generated, but best I can tell, this is not possible. AFAIK the best you could do is a dynamic check that the void* conversion after the static cast is unchanged. Pull Request resolved: https://github.com/facebook/rocksdb/pull/12308 Test Plan: existing tests, CI Reviewed By: ltamasi Differential Revision: D53204947 Pulled By: pdillinger fbshipit-source-id: 9de23e618263b0d5b9820f4e15966876888a16e2
134 lines
4.4 KiB
C++
134 lines
4.4 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#include "rocksdb/customizable.h"
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#include <sstream>
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#include "options/options_helper.h"
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#include "port/port.h"
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#include "rocksdb/convenience.h"
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#include "rocksdb/status.h"
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#include "rocksdb/utilities/options_type.h"
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#include "util/string_util.h"
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namespace ROCKSDB_NAMESPACE {
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std::string Customizable::GetOptionName(const std::string& long_name) const {
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const std::string& name = Name();
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size_t name_len = name.size();
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if (long_name.size() > name_len + 1 &&
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long_name.compare(0, name_len, name) == 0 &&
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long_name.at(name_len) == '.') {
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return long_name.substr(name_len + 1);
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} else {
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return Configurable::GetOptionName(long_name);
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}
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}
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std::string Customizable::GenerateIndividualId() const {
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std::ostringstream ostr;
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ostr << Name() << "@" << static_cast<const void*>(this) << "#"
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<< port::GetProcessID();
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return ostr.str();
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}
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Status Customizable::GetOption(const ConfigOptions& config_options,
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const std::string& opt_name,
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std::string* value) const {
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if (opt_name == OptionTypeInfo::kIdPropName()) {
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*value = GetId();
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return Status::OK();
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} else {
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return Configurable::GetOption(config_options, opt_name, value);
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}
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}
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std::string Customizable::SerializeOptions(const ConfigOptions& config_options,
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const std::string& prefix) const {
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std::string result;
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std::string parent;
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std::string id = GetId();
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if (!config_options.IsShallow() && !id.empty()) {
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parent = Configurable::SerializeOptions(config_options, "");
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}
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if (parent.empty()) {
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result = id;
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} else {
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result.append(prefix);
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result.append(OptionTypeInfo::kIdPropName());
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result.append("=");
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result.append(id);
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result.append(config_options.delimiter);
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result.append(parent);
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}
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return result;
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}
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bool Customizable::AreEquivalent(const ConfigOptions& config_options,
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const Configurable* other,
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std::string* mismatch) const {
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if (config_options.sanity_level > ConfigOptions::kSanityLevelNone &&
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this != other) {
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const Customizable* custom = static_cast<const Customizable*>(other);
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if (custom == nullptr) { // Cast failed
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return false;
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} else if (GetId() != custom->GetId()) {
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*mismatch = OptionTypeInfo::kIdPropName();
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return false;
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} else if (config_options.sanity_level >
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ConfigOptions::kSanityLevelLooselyCompatible) {
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bool matches =
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Configurable::AreEquivalent(config_options, other, mismatch);
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return matches;
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}
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}
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return true;
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}
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Status Customizable::GetOptionsMap(
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const ConfigOptions& config_options, const Customizable* customizable,
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const std::string& value, std::string* id,
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std::unordered_map<std::string, std::string>* props) {
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Status status;
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if (value.empty() || value == kNullptrString) {
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*id = "";
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props->clear();
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} else if (customizable != nullptr) {
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status =
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Configurable::GetOptionsMap(value, customizable->GetId(), id, props);
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if (status.ok() && customizable->IsInstanceOf(*id)) {
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// The new ID and the old ID match, so the objects are the same type.
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// Try to get the existing options, ignoring any errors
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ConfigOptions embedded = config_options;
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embedded.delimiter = ";";
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std::string curr_opts;
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if (customizable->GetOptionString(embedded, &curr_opts).ok()) {
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std::unordered_map<std::string, std::string> curr_props;
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if (StringToMap(curr_opts, &curr_props).ok()) {
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props->insert(curr_props.begin(), curr_props.end());
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}
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}
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}
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} else {
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status = Configurable::GetOptionsMap(value, "", id, props);
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}
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return status;
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}
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Status Customizable::ConfigureNewObject(
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const ConfigOptions& config_options, Customizable* object,
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const std::unordered_map<std::string, std::string>& opt_map) {
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Status status;
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if (object != nullptr) {
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status = object->ConfigureFromMap(config_options, opt_map);
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} else if (!opt_map.empty()) {
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status = Status::InvalidArgument("Cannot configure null object ");
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}
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return status;
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}
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} // namespace ROCKSDB_NAMESPACE
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