src/traced/probes/ftrace/proto_translation_table.cc - third_party/perfetto - Git at Google

 /*
  * Copyright (C) 2017 The Android Open Source Project
  *
  * 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.
  */

 #include "src/traced/probes/ftrace/proto_translation_table.h"

 #include <regex.h>
 #include <sys/utsname.h>

 #include <algorithm>

 #include "perfetto/ext/base/string_utils.h"
 #include "perfetto/protozero/proto_utils.h"
 #include "src/traced/probes/ftrace/event_info.h"
 #include "src/traced/probes/ftrace/ftrace_procfs.h"

 #include "protos/perfetto/trace/ftrace/ftrace_event.pbzero.h"
 #include "protos/perfetto/trace/ftrace/ftrace_event_bundle.pbzero.h"
 #include "protos/perfetto/trace/ftrace/generic.pbzero.h"

 namespace perfetto {

 namespace {

 using protos::pbzero::GenericFtraceEvent;
 using protozero::proto_utils::ProtoSchemaType;

 ProtoTranslationTable::FtracePageHeaderSpec MakeFtracePageHeaderSpec(
     const std::vector<FtraceEvent::Field>& fields) {
   ProtoTranslationTable::FtracePageHeaderSpec spec;
   for (const FtraceEvent::Field& field : fields) {
     std::string name = GetNameFromTypeAndName(field.type_and_name);
     if (name == "timestamp")
       spec.timestamp = field;
     else if (name == "commit")
       spec.size = field;
     else if (name == "overwrite")
       spec.overwrite = field;
     else if (name != "data")
       PERFETTO_DFATAL("Invalid field in header spec: %s", name.c_str());
   }
   return spec;
 }

 // Fallback used when the "header_page" is not readable.
 // It uses a hard-coded header_page. The only caveat is that the size of the
 // |commit| field depends on the kernel bit-ness. This function tries to infer
 // that from the uname() and if that fails assumes that the kernel bitness
 // matches the userspace bitness.
 ProtoTranslationTable::FtracePageHeaderSpec GuessFtracePageHeaderSpec() {
   ProtoTranslationTable::FtracePageHeaderSpec spec{};
 #if PERFETTO_BUILDFLAG(PERFETTO_OS_ANDROID) && __i386__
   // local_t is arch-specific and models the largest size of an integer that is
   // still atomic across bus transactions, exceptions and IRQ. On android x86
   // this is always size 8
   uint16_t commit_size = 8;
 #else
   uint16_t commit_size = sizeof(long);

   struct utsname sysinfo;
   // If user space is 32-bit check the kernel to verify.
   if (commit_size < 8 && uname(&sysinfo) == 0) {
     // Arm returns armv# for its machine type. The first (and only currently)
     // arm processor that supports 64bit is the armv8 series.
     commit_size =
         strstr(sysinfo.machine, "64") || strstr(sysinfo.machine, "armv8") ? 8
                                                                           : 4;
   }
 #endif

   // header_page typically looks as follows on a 64-bit kernel:
   // field: u64 timestamp; offset:0; size:8; signed:0;
   // field: local_t commit; offset:8; size:8; signed:1;
   // field: int overwrite; offset:8; size:1; signed:1;
   // field: char data; offset:16; size:4080; signed:0;
   //
   // On a 32-bit kernel local_t is 32-bit wide and data starts @ offset 12.

   spec.timestamp = FtraceEvent::Field{"u64 timestamp", 0, 8, 0};
   spec.size = FtraceEvent::Field{"local_t commit", 8, commit_size, 1};
   spec.overwrite = FtraceEvent::Field{"int overwrite", 8, 1, 1};
   return spec;
 }

 const std::vector<Event> BuildEventsVector(const std::vector<Event>& events) {
   size_t largest_id = 0;
   for (const Event& event : events) {
     if (event.ftrace_event_id > largest_id)
       largest_id = event.ftrace_event_id;
   }
   std::vector<Event> events_by_id;
   events_by_id.resize(largest_id + 1);
   for (const Event& event : events) {
     events_by_id[event.ftrace_event_id] = event;
   }
   events_by_id.shrink_to_fit();
   return events_by_id;
 }

 // Merge the information from |ftrace_field| into |field| (mutating it).
 // We should set the following fields: offset, size, ftrace field type and
 // translation strategy.
 bool MergeFieldInfo(const FtraceEvent::Field& ftrace_field,
                     Field* field,
                     const char* event_name_for_debug) {
   PERFETTO_DCHECK(field->ftrace_name);
   PERFETTO_DCHECK(field->proto_field_id);
   PERFETTO_DCHECK(static_cast<int>(field->proto_field_type));
   PERFETTO_DCHECK(!field->ftrace_offset);
   PERFETTO_DCHECK(!field->ftrace_size);
   PERFETTO_DCHECK(!field->ftrace_type);

   if (!InferFtraceType(ftrace_field.type_and_name, ftrace_field.size,
                        ftrace_field.is_signed, &field->ftrace_type)) {
     PERFETTO_FATAL(
         "Failed to infer ftrace field type for \"%s.%s\" (type:\"%s\" "
         "size:%d "
         "signed:%d)",
         event_name_for_debug, field->ftrace_name,
         ftrace_field.type_and_name.c_str(), ftrace_field.size,
         ftrace_field.is_signed);
     return false;
   }

   field->ftrace_offset = ftrace_field.offset;
   field->ftrace_size = ftrace_field.size;

   if (!SetTranslationStrategy(field->ftrace_type, field->proto_field_type,
                               &field->strategy)) {
     PERFETTO_DLOG(
         "Failed to find translation strategy for ftrace field \"%s.%s\" (%s -> "
         "%s)",
         event_name_for_debug, field->ftrace_name, ToString(field->ftrace_type),
         protozero::proto_utils::ProtoSchemaToString(field->proto_field_type));
     // TODO(hjd): Uncomment DCHECK when proto generation is fixed.
     // PERFETTO_DFATAL("Failed to find translation strategy");
     return false;
   }

   return true;
 }

 // For each field in |fields| find the matching field from |ftrace_fields| (by
 // comparing ftrace_name) and copy the information from the FtraceEvent::Field
 // into the Field (mutating it). If there is no matching field in
 // |ftrace_fields| remove the Field from |fields|. Return the maximum observed
 // 'field end' (offset + size).
 uint16_t MergeFields(const std::vector<FtraceEvent::Field>& ftrace_fields,
                      std::vector<Field>* fields,
                      const char* event_name_for_debug) {
   uint16_t fields_end = 0;

   // Loop over each Field in |fields| modifying it with information from the
   // matching |ftrace_fields| field or removing it.
   auto field = fields->begin();
   while (field != fields->end()) {
     bool success = false;
     for (const FtraceEvent::Field& ftrace_field : ftrace_fields) {
       if (GetNameFromTypeAndName(ftrace_field.type_and_name) !=
           field->ftrace_name)
         continue;

       success = MergeFieldInfo(ftrace_field, &*field, event_name_for_debug);

       uint16_t field_end = field->ftrace_offset + field->ftrace_size;
       fields_end = std::max<uint16_t>(fields_end, field_end);

       break;
     }
     if (success) {
       ++field;
     } else {
       field = fields->erase(field);
     }
   }
   return fields_end;
 }

 bool Contains(const std::string& haystack, const std::string& needle) {
   return haystack.find(needle) != std::string::npos;
 }

 std::string RegexError(int errcode, const regex_t* preg) {
   char buf[64];
   regerror(errcode, preg, buf, sizeof(buf));
   return {buf, sizeof(buf)};
 }

 bool Match(const char* string, const char* pattern) {
   regex_t re;
   int ret = regcomp(&re, pattern, REG_EXTENDED | REG_NOSUB);
   if (ret != 0) {
     PERFETTO_FATAL("regcomp: %s", RegexError(ret, &re).c_str());
   }
   ret = regexec(&re, string, 0, nullptr, 0);
   regfree(&re);
   return ret != REG_NOMATCH;
 }

 // Set proto field type and id based on the ftrace type.
 void SetProtoType(FtraceFieldType ftrace_type,
                   ProtoSchemaType* proto_type,
                   uint32_t* proto_field_id) {
   switch (ftrace_type) {
     case kFtraceCString:
     case kFtraceFixedCString:
     case kFtraceStringPtr:
     case kFtraceDataLoc:
       *proto_type = ProtoSchemaType::kString;
       *proto_field_id = GenericFtraceEvent::Field::kStrValueFieldNumber;
       break;
     case kFtraceInt8:
     case kFtraceInt16:
     case kFtraceInt32:
     case kFtracePid32:
     case kFtraceCommonPid32:
     case kFtraceInt64:
       *proto_type = ProtoSchemaType::kInt64;
       *proto_field_id = GenericFtraceEvent::Field::kIntValueFieldNumber;
       break;
     case kFtraceUint8:
     case kFtraceUint16:
     case kFtraceUint32:
     case kFtraceBool:
     case kFtraceDevId32:
     case kFtraceDevId64:
     case kFtraceUint64:
     case kFtraceInode32:
     case kFtraceInode64:
       *proto_type = ProtoSchemaType::kUint64;
       *proto_field_id = GenericFtraceEvent::Field::kUintValueFieldNumber;
       break;
   }
 }

 }  // namespace

 // This is similar but different from InferProtoType (see format_parser.cc).
 // TODO(hjd): Fold FtraceEvent(::Field) into Event.
 bool InferFtraceType(const std::string& type_and_name,
                      size_t size,
                      bool is_signed,
                      FtraceFieldType* out) {
   // Fixed length strings: e.g. "char foo[16]" we don't care about the number
   // since we get the size as it's own field. Somewhat awkwardly these fields
   // are both fixed size and null terminated meaning that we can't just drop
   // them directly into the protobuf (since if the string is shorter than 15
   // characters we want only the bit up to the null terminator).
   if (Match(type_and_name.c_str(), R"(char [a-zA-Z_]+\[[0-9]+\])")) {
     *out = kFtraceFixedCString;
     return true;
   }

   // String pointers: "__data_loc char[] foo" (as in
   // 'cpufreq_interactive_boost').
   // TODO(fmayer): Handle u32[], u8[], __u8[] as well.
   if (Contains(type_and_name, "__data_loc char[] ")) {
     if (size != 4) {
       PERFETTO_ELOG("__data_loc with incorrect size: %s (%zd)",
                     type_and_name.c_str(), size);
       return false;
     }
     *out = kFtraceDataLoc;
     return true;
   }

   if (Contains(type_and_name, "char[] ")) {
     *out = kFtraceStringPtr;
     return true;
   }
   if (Contains(type_and_name, "char * ")) {
     *out = kFtraceStringPtr;
     return true;
   }

   // Variable length strings: "char foo" + size: 0 (as in 'print').
   if (base::StartsWith(type_and_name, "char ") && size == 0) {
     *out = kFtraceCString;
     return true;
   }

   if (base::StartsWith(type_and_name, "bool ")) {
     *out = kFtraceBool;
     return true;
   }

   if (base::StartsWith(type_and_name, "ino_t ") ||
       base::StartsWith(type_and_name, "i_ino ")) {
     if (size == 4) {
       *out = kFtraceInode32;
       return true;
     } else if (size == 8) {
       *out = kFtraceInode64;
       return true;
     }
   }

   if (base::StartsWith(type_and_name, "dev_t ")) {
     if (size == 4) {
       *out = kFtraceDevId32;
       return true;
     } else if (size == 8) {
       *out = kFtraceDevId64;
       return true;
     }
   }

   // Pids (as in 'sched_switch').
   if (base::StartsWith(type_and_name, "pid_t ") && size == 4) {
     *out = kFtracePid32;
     return true;
   }

   if (Contains(type_and_name, "common_pid") && size == 4) {
     *out = kFtraceCommonPid32;
     return true;
   }

   // Ints of various sizes:
   if (size == 1 && is_signed) {
     *out = kFtraceInt8;
     return true;
   } else if (size == 1 && !is_signed) {
     *out = kFtraceUint8;
     return true;
   } else if (size == 2 && is_signed) {
     *out = kFtraceInt16;
     return true;
   } else if (size == 2 && !is_signed) {
     *out = kFtraceUint16;
     return true;
   } else if (size == 4 && is_signed) {
     *out = kFtraceInt32;
     return true;
   } else if (size == 4 && !is_signed) {
     *out = kFtraceUint32;
     return true;
   } else if (size == 8 && is_signed) {
     *out = kFtraceInt64;
     return true;
   } else if (size == 8 && !is_signed) {
     *out = kFtraceUint64;
     return true;
   }

   PERFETTO_DLOG("Could not infer ftrace type for '%s'", type_and_name.c_str());
   return false;
 }

 // static
 ProtoTranslationTable::FtracePageHeaderSpec
 ProtoTranslationTable::DefaultPageHeaderSpecForTesting() {
   std::string page_header =
       R"(	field: u64 timestamp;	offset:0;	size:8;	signed:0;
 	field: local_t commit;	offset:8;	size:8;	signed:1;
 	field: int overwrite;	offset:8;	size:1;	signed:1;
 	field: char data;	offset:16;	size:4080;	signed:0;)";
   std::vector<FtraceEvent::Field> page_header_fields;
   PERFETTO_CHECK(ParseFtraceEventBody(std::move(page_header), nullptr,
                                       &page_header_fields));
   return MakeFtracePageHeaderSpec(page_header_fields);
 }

 // static
 std::unique_ptr<ProtoTranslationTable> ProtoTranslationTable::Create(
     const FtraceProcfs* ftrace_procfs,
     std::vector<Event> events,
     std::vector<Field> common_fields) {
   bool common_fields_processed = false;
   uint16_t common_fields_end = 0;

   std::string page_header = ftrace_procfs->ReadPageHeaderFormat();
   bool ftrace_header_parsed = false;
   FtracePageHeaderSpec header_spec{};
   if (!page_header.empty()) {
     std::vector<FtraceEvent::Field> page_header_fields;
     ftrace_header_parsed = ParseFtraceEventBody(std::move(page_header), nullptr,
                                                 &page_header_fields);
     header_spec = MakeFtracePageHeaderSpec(page_header_fields);
   }

   if (!ftrace_header_parsed) {
     PERFETTO_LOG("Failed to parse ftrace page header, using fallback layout");
     header_spec = GuessFtracePageHeaderSpec();
   }

   for (Event& event : events) {
     if (event.proto_field_id ==
         protos::pbzero::FtraceEvent::kGenericFieldNumber) {
       continue;
     }
     PERFETTO_DCHECK(event.name);
     PERFETTO_DCHECK(event.group);
     PERFETTO_DCHECK(event.proto_field_id);
     PERFETTO_DCHECK(!event.ftrace_event_id);

     std::string contents =
         ftrace_procfs->ReadEventFormat(event.group, event.name);
     FtraceEvent ftrace_event;
     if (contents.empty() || !ParseFtraceEvent(contents, &ftrace_event)) {
       if (!strcmp(event.group, "ftrace") && !strcmp(event.name, "print")) {
         // On some "user" builds of Android <P the ftrace/print event is not
         // selinux-whitelisted. Thankfully this event is an always-on built-in
         // so we don't need to write to its 'enable' file. However we need to
         // know its binary layout to decode it, so we hardcode it.
         ftrace_event.id = 5;  // Seems quite stable across kernels.
         ftrace_event.name = "print";
         // The only field we care about is:
         // field:char buf; offset:16; size:0; signed:0;
         ftrace_event.fields.emplace_back(
             FtraceEvent::Field{"char buf", 16, 0, 0});
       } else {
         continue;
       }
     }

     event.ftrace_event_id = ftrace_event.id;

     if (!common_fields_processed) {
       common_fields_end =
           MergeFields(ftrace_event.common_fields, &common_fields, event.name);
       common_fields_processed = true;
     }

     uint16_t fields_end =
         MergeFields(ftrace_event.fields, &event.fields, event.name);

     event.size = std::max<uint16_t>(fields_end, common_fields_end);
   }

   events.erase(std::remove_if(events.begin(), events.end(),
                               [](const Event& event) {
                                 return event.proto_field_id == 0 ||
                                        event.ftrace_event_id == 0;
                               }),
                events.end());

   auto table = std::unique_ptr<ProtoTranslationTable>(new ProtoTranslationTable(
       ftrace_procfs, events, std::move(common_fields), header_spec));
   return table;
 }

 ProtoTranslationTable::ProtoTranslationTable(
     const FtraceProcfs* ftrace_procfs,
     const std::vector<Event>& events,
     std::vector<Field> common_fields,
     FtracePageHeaderSpec ftrace_page_header_spec)
     : ftrace_procfs_(ftrace_procfs),
       events_(BuildEventsVector(events)),
       largest_id_(events_.size() - 1),
       common_fields_(std::move(common_fields)),
       ftrace_page_header_spec_(ftrace_page_header_spec) {
   for (const Event& event : events) {
     group_and_name_to_event_[GroupAndName(event.group, event.name)] =
         &events_.at(event.ftrace_event_id);
     name_to_events_[event.name].push_back(&events_.at(event.ftrace_event_id));
     group_to_events_[event.group].push_back(&events_.at(event.ftrace_event_id));
   }
 }

 const Event* ProtoTranslationTable::GetOrCreateEvent(
     const GroupAndName& group_and_name) {
   const Event* event = GetEvent(group_and_name);
   if (event)
     return event;
   // The ftrace event does not already exist so a new one will be created
   // by parsing the format file.
   std::string contents = ftrace_procfs_->ReadEventFormat(group_and_name.group(),
                                                          group_and_name.name());
   if (contents.empty())
     return nullptr;
   FtraceEvent ftrace_event = {};
   ParseFtraceEvent(contents, &ftrace_event);

   // Ensure events vector is large enough
   if (ftrace_event.id > largest_id_) {
     events_.resize(ftrace_event.id + 1);
     largest_id_ = ftrace_event.id;
   }

   // Set known event variables
   Event* e = &events_.at(ftrace_event.id);
   e->ftrace_event_id = ftrace_event.id;
   e->proto_field_id = protos::pbzero::FtraceEvent::kGenericFieldNumber;
   e->name = InternString(group_and_name.name());
   e->group = InternString(group_and_name.group());

   // Calculate size of common fields.
   for (const FtraceEvent::Field& ftrace_field : ftrace_event.common_fields) {
     uint16_t field_end = ftrace_field.offset + ftrace_field.size;
     e->size = std::max(field_end, e->size);
   }

   // For every field in the ftrace event, make a field in the generic event.
   for (const FtraceEvent::Field& ftrace_field : ftrace_event.fields)
     e->size = std::max(CreateGenericEventField(ftrace_field, *e), e->size);

   group_and_name_to_event_[group_and_name] = &events_.at(e->ftrace_event_id);
   name_to_events_[e->name].push_back(&events_.at(e->ftrace_event_id));
   group_to_events_[e->group].push_back(&events_.at(e->ftrace_event_id));

   return e;
 };

 const char* ProtoTranslationTable::InternString(const std::string& str) {
   auto it_and_inserted = interned_strings_.insert(str);
   return it_and_inserted.first->c_str();
 };

 uint16_t ProtoTranslationTable::CreateGenericEventField(
     const FtraceEvent::Field& ftrace_field,
     Event& event) {
   uint16_t field_end = ftrace_field.offset + ftrace_field.size;
   std::string field_name = GetNameFromTypeAndName(ftrace_field.type_and_name);
   if (field_name.empty()) {
     PERFETTO_DLOG("Field: %s could not be added to the generic event.",
                   ftrace_field.type_and_name.c_str());
     return field_end;
   }
   event.fields.emplace_back();
   Field* field = &event.fields.back();
   field->ftrace_name = InternString(field_name);
   if (!InferFtraceType(ftrace_field.type_and_name, ftrace_field.size,
                        ftrace_field.is_signed, &field->ftrace_type)) {
     PERFETTO_DLOG(
         "Failed to infer ftrace field type for \"%s.%s\" (type:\"%s\" "
         "size:%d "
         "signed:%d)",
         event.name, field->ftrace_name, ftrace_field.type_and_name.c_str(),
         ftrace_field.size, ftrace_field.is_signed);
     event.fields.pop_back();
     return field_end;
   }
   SetProtoType(field->ftrace_type, &field->proto_field_type,
                &field->proto_field_id);
   field->ftrace_offset = ftrace_field.offset;
   field->ftrace_size = ftrace_field.size;
   // Proto type is set based on ftrace type so all fields should have a
   // translation strategy.
   bool success = SetTranslationStrategy(
       field->ftrace_type, field->proto_field_type, &field->strategy);
   PERFETTO_DCHECK(success);
   return field_end;
 }

 EventFilter::EventFilter() = default;
 EventFilter::~EventFilter() = default;

 void EventFilter::AddEnabledEvent(size_t ftrace_event_id) {
   if (ftrace_event_id >= enabled_ids_.size())
     enabled_ids_.resize(ftrace_event_id + 1);
   enabled_ids_[ftrace_event_id] = true;
 }

 void EventFilter::DisableEvent(size_t ftrace_event_id) {
   if (ftrace_event_id >= enabled_ids_.size())
     return;
   enabled_ids_[ftrace_event_id] = false;
 }

 bool EventFilter::IsEventEnabled(size_t ftrace_event_id) const {
   if (ftrace_event_id == 0 || ftrace_event_id >= enabled_ids_.size())
     return false;
   return enabled_ids_[ftrace_event_id];
 }

 std::set<size_t> EventFilter::GetEnabledEvents() const {
   std::set<size_t> enabled;
   for (size_t i = 0; i < enabled_ids_.size(); i++) {
     if (enabled_ids_[i]) {
       enabled.insert(i);
     }
   }
   return enabled;
 }

 void EventFilter::EnableEventsFrom(const EventFilter& other) {
   size_t max_length = std::max(enabled_ids_.size(), other.enabled_ids_.size());
   enabled_ids_.resize(max_length);
   for (size_t i = 0; i < other.enabled_ids_.size(); i++) {
     if (other.enabled_ids_[i])
       enabled_ids_[i] = true;
   }
 }

 ProtoTranslationTable::~ProtoTranslationTable() = default;

 }  // namespace perfetto
	/*
	* Copyright (C) 2017 The Android Open Source Project
	*
	* 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.
	*/

	#include "src/traced/probes/ftrace/proto_translation_table.h"

	#include <regex.h>
	#include <sys/utsname.h>

	#include <algorithm>

	#include "perfetto/ext/base/string_utils.h"
	#include "perfetto/protozero/proto_utils.h"
	#include "src/traced/probes/ftrace/event_info.h"
	#include "src/traced/probes/ftrace/ftrace_procfs.h"

	#include "protos/perfetto/trace/ftrace/ftrace_event.pbzero.h"
	#include "protos/perfetto/trace/ftrace/ftrace_event_bundle.pbzero.h"
	#include "protos/perfetto/trace/ftrace/generic.pbzero.h"

	namespace perfetto {

	namespace {

	using protos::pbzero::GenericFtraceEvent;
	using protozero::proto_utils::ProtoSchemaType;

	ProtoTranslationTable::FtracePageHeaderSpec MakeFtracePageHeaderSpec(
	const std::vector<FtraceEvent::Field>& fields) {
	ProtoTranslationTable::FtracePageHeaderSpec spec;
	for (const FtraceEvent::Field& field : fields) {
	std::string name = GetNameFromTypeAndName(field.type_and_name);
	if (name == "timestamp")
	spec.timestamp = field;
	else if (name == "commit")
	spec.size = field;
	else if (name == "overwrite")
	spec.overwrite = field;
	else if (name != "data")
	PERFETTO_DFATAL("Invalid field in header spec: %s", name.c_str());
	}
	return spec;
	}

	// Fallback used when the "header_page" is not readable.
	// It uses a hard-coded header_page. The only caveat is that the size of the
	// \|commit\| field depends on the kernel bit-ness. This function tries to infer
	// that from the uname() and if that fails assumes that the kernel bitness
	// matches the userspace bitness.
	ProtoTranslationTable::FtracePageHeaderSpec GuessFtracePageHeaderSpec() {
	ProtoTranslationTable::FtracePageHeaderSpec spec{};
	#if PERFETTO_BUILDFLAG(PERFETTO_OS_ANDROID) && __i386__
	// local_t is arch-specific and models the largest size of an integer that is
	// still atomic across bus transactions, exceptions and IRQ. On android x86
	// this is always size 8
	uint16_t commit_size = 8;
	#else
	uint16_t commit_size = sizeof(long);

	struct utsname sysinfo;
	// If user space is 32-bit check the kernel to verify.
	if (commit_size < 8 && uname(&sysinfo) == 0) {
	// Arm returns armv# for its machine type. The first (and only currently)
	// arm processor that supports 64bit is the armv8 series.
	commit_size =
	strstr(sysinfo.machine, "64") \|\| strstr(sysinfo.machine, "armv8") ? 8
	: 4;
	}
	#endif

	// header_page typically looks as follows on a 64-bit kernel:
	// field: u64 timestamp; offset:0; size:8; signed:0;
	// field: local_t commit; offset:8; size:8; signed:1;
	// field: int overwrite; offset:8; size:1; signed:1;
	// field: char data; offset:16; size:4080; signed:0;
	//
	// On a 32-bit kernel local_t is 32-bit wide and data starts @ offset 12.

	spec.timestamp = FtraceEvent::Field{"u64 timestamp", 0, 8, 0};
	spec.size = FtraceEvent::Field{"local_t commit", 8, commit_size, 1};
	spec.overwrite = FtraceEvent::Field{"int overwrite", 8, 1, 1};
	return spec;
	}

	const std::vector<Event> BuildEventsVector(const std::vector<Event>& events) {
	size_t largest_id = 0;
	for (const Event& event : events) {
	if (event.ftrace_event_id > largest_id)
	largest_id = event.ftrace_event_id;
	}
	std::vector<Event> events_by_id;
	events_by_id.resize(largest_id + 1);
	for (const Event& event : events) {
	events_by_id[event.ftrace_event_id] = event;
	}
	events_by_id.shrink_to_fit();
	return events_by_id;
	}

	// Merge the information from \|ftrace_field\| into \|field\| (mutating it).
	// We should set the following fields: offset, size, ftrace field type and
	// translation strategy.
	bool MergeFieldInfo(const FtraceEvent::Field& ftrace_field,
	Field* field,
	const char* event_name_for_debug) {
	PERFETTO_DCHECK(field->ftrace_name);
	PERFETTO_DCHECK(field->proto_field_id);
	PERFETTO_DCHECK(static_cast<int>(field->proto_field_type));
	PERFETTO_DCHECK(!field->ftrace_offset);
	PERFETTO_DCHECK(!field->ftrace_size);
	PERFETTO_DCHECK(!field->ftrace_type);

	if (!InferFtraceType(ftrace_field.type_and_name, ftrace_field.size,
	ftrace_field.is_signed, &field->ftrace_type)) {
	PERFETTO_FATAL(
	"Failed to infer ftrace field type for \"%s.%s\" (type:\"%s\" "
	"size:%d "
	"signed:%d)",
	event_name_for_debug, field->ftrace_name,
	ftrace_field.type_and_name.c_str(), ftrace_field.size,
	ftrace_field.is_signed);
	return false;
	}

	field->ftrace_offset = ftrace_field.offset;
	field->ftrace_size = ftrace_field.size;

	if (!SetTranslationStrategy(field->ftrace_type, field->proto_field_type,
	&field->strategy)) {
	PERFETTO_DLOG(
	"Failed to find translation strategy for ftrace field \"%s.%s\" (%s -> "
	"%s)",
	event_name_for_debug, field->ftrace_name, ToString(field->ftrace_type),
	protozero::proto_utils::ProtoSchemaToString(field->proto_field_type));
	// TODO(hjd): Uncomment DCHECK when proto generation is fixed.
	// PERFETTO_DFATAL("Failed to find translation strategy");
	return false;
	}

	return true;
	}

	// For each field in \|fields\| find the matching field from \|ftrace_fields\| (by
	// comparing ftrace_name) and copy the information from the FtraceEvent::Field
	// into the Field (mutating it). If there is no matching field in
	// \|ftrace_fields\| remove the Field from \|fields\|. Return the maximum observed
	// 'field end' (offset + size).
	uint16_t MergeFields(const std::vector<FtraceEvent::Field>& ftrace_fields,
	std::vector<Field>* fields,
	const char* event_name_for_debug) {
	uint16_t fields_end = 0;

	// Loop over each Field in \|fields\| modifying it with information from the
	// matching \|ftrace_fields\| field or removing it.
	auto field = fields->begin();
	while (field != fields->end()) {
	bool success = false;
	for (const FtraceEvent::Field& ftrace_field : ftrace_fields) {
	if (GetNameFromTypeAndName(ftrace_field.type_and_name) !=
	field->ftrace_name)
	continue;

	success = MergeFieldInfo(ftrace_field, &*field, event_name_for_debug);

	uint16_t field_end = field->ftrace_offset + field->ftrace_size;
	fields_end = std::max<uint16_t>(fields_end, field_end);

	break;
	}
	if (success) {
	++field;
	} else {
	field = fields->erase(field);
	}
	}
	return fields_end;
	}

	bool Contains(const std::string& haystack, const std::string& needle) {
	return haystack.find(needle) != std::string::npos;
	}

	std::string RegexError(int errcode, const regex_t* preg) {
	char buf[64];
	regerror(errcode, preg, buf, sizeof(buf));
	return {buf, sizeof(buf)};
	}

	bool Match(const char* string, const char* pattern) {
	regex_t re;
	int ret = regcomp(&re, pattern, REG_EXTENDED \| REG_NOSUB);
	if (ret != 0) {
	PERFETTO_FATAL("regcomp: %s", RegexError(ret, &re).c_str());
	}
	ret = regexec(&re, string, 0, nullptr, 0);
	regfree(&re);
	return ret != REG_NOMATCH;
	}

	// Set proto field type and id based on the ftrace type.
	void SetProtoType(FtraceFieldType ftrace_type,
	ProtoSchemaType* proto_type,
	uint32_t* proto_field_id) {
	switch (ftrace_type) {
	case kFtraceCString:
	case kFtraceFixedCString:
	case kFtraceStringPtr:
	case kFtraceDataLoc:
	*proto_type = ProtoSchemaType::kString;
	*proto_field_id = GenericFtraceEvent::Field::kStrValueFieldNumber;
	break;
	case kFtraceInt8:
	case kFtraceInt16:
	case kFtraceInt32:
	case kFtracePid32:
	case kFtraceCommonPid32:
	case kFtraceInt64:
	*proto_type = ProtoSchemaType::kInt64;
	*proto_field_id = GenericFtraceEvent::Field::kIntValueFieldNumber;
	break;
	case kFtraceUint8:
	case kFtraceUint16:
	case kFtraceUint32:
	case kFtraceBool:
	case kFtraceDevId32:
	case kFtraceDevId64:
	case kFtraceUint64:
	case kFtraceInode32:
	case kFtraceInode64:
	*proto_type = ProtoSchemaType::kUint64;
	*proto_field_id = GenericFtraceEvent::Field::kUintValueFieldNumber;
	break;
	}
	}

	} // namespace

	// This is similar but different from InferProtoType (see format_parser.cc).
	// TODO(hjd): Fold FtraceEvent(::Field) into Event.
	bool InferFtraceType(const std::string& type_and_name,
	size_t size,
	bool is_signed,
	FtraceFieldType* out) {
	// Fixed length strings: e.g. "char foo[16]" we don't care about the number
	// since we get the size as it's own field. Somewhat awkwardly these fields
	// are both fixed size and null terminated meaning that we can't just drop
	// them directly into the protobuf (since if the string is shorter than 15
	// characters we want only the bit up to the null terminator).
	if (Match(type_and_name.c_str(), R"(char [a-zA-Z_]+\[[0-9]+\])")) {
	*out = kFtraceFixedCString;
	return true;
	}

	// String pointers: "__data_loc char[] foo" (as in
	// 'cpufreq_interactive_boost').
	// TODO(fmayer): Handle u32[], u8[], __u8[] as well.
	if (Contains(type_and_name, "__data_loc char[] ")) {
	if (size != 4) {
	PERFETTO_ELOG("__data_loc with incorrect size: %s (%zd)",
	type_and_name.c_str(), size);
	return false;
	}
	*out = kFtraceDataLoc;
	return true;
	}

	if (Contains(type_and_name, "char[] ")) {
	*out = kFtraceStringPtr;
	return true;
	}
	if (Contains(type_and_name, "char * ")) {
	*out = kFtraceStringPtr;
	return true;
	}

	// Variable length strings: "char foo" + size: 0 (as in 'print').
	if (base::StartsWith(type_and_name, "char ") && size == 0) {
	*out = kFtraceCString;
	return true;
	}

	if (base::StartsWith(type_and_name, "bool ")) {
	*out = kFtraceBool;
	return true;
	}

	if (base::StartsWith(type_and_name, "ino_t ") \|\|
	base::StartsWith(type_and_name, "i_ino ")) {
	if (size == 4) {
	*out = kFtraceInode32;
	return true;
	} else if (size == 8) {
	*out = kFtraceInode64;
	return true;
	}
	}

	if (base::StartsWith(type_and_name, "dev_t ")) {
	if (size == 4) {
	*out = kFtraceDevId32;
	return true;
	} else if (size == 8) {
	*out = kFtraceDevId64;
	return true;
	}
	}

	// Pids (as in 'sched_switch').
	if (base::StartsWith(type_and_name, "pid_t ") && size == 4) {
	*out = kFtracePid32;
	return true;
	}

	if (Contains(type_and_name, "common_pid") && size == 4) {
	*out = kFtraceCommonPid32;
	return true;
	}

	// Ints of various sizes:
	if (size == 1 && is_signed) {
	*out = kFtraceInt8;
	return true;
	} else if (size == 1 && !is_signed) {
	*out = kFtraceUint8;
	return true;
	} else if (size == 2 && is_signed) {
	*out = kFtraceInt16;
	return true;
	} else if (size == 2 && !is_signed) {
	*out = kFtraceUint16;
	return true;
	} else if (size == 4 && is_signed) {
	*out = kFtraceInt32;
	return true;
	} else if (size == 4 && !is_signed) {
	*out = kFtraceUint32;
	return true;
	} else if (size == 8 && is_signed) {
	*out = kFtraceInt64;
	return true;
	} else if (size == 8 && !is_signed) {
	*out = kFtraceUint64;
	return true;
	}

	PERFETTO_DLOG("Could not infer ftrace type for '%s'", type_and_name.c_str());
	return false;
	}

	// static
	ProtoTranslationTable::FtracePageHeaderSpec
	ProtoTranslationTable::DefaultPageHeaderSpecForTesting() {
	std::string page_header =
	R"( field: u64 timestamp; offset:0; size:8; signed:0;
	field: local_t commit; offset:8; size:8; signed:1;
	field: int overwrite; offset:8; size:1; signed:1;
	field: char data; offset:16; size:4080; signed:0;)";
	std::vector<FtraceEvent::Field> page_header_fields;
	PERFETTO_CHECK(ParseFtraceEventBody(std::move(page_header), nullptr,
	&page_header_fields));
	return MakeFtracePageHeaderSpec(page_header_fields);
	}

	// static
	std::unique_ptr<ProtoTranslationTable> ProtoTranslationTable::Create(
	const FtraceProcfs* ftrace_procfs,
	std::vector<Event> events,
	std::vector<Field> common_fields) {
	bool common_fields_processed = false;
	uint16_t common_fields_end = 0;

	std::string page_header = ftrace_procfs->ReadPageHeaderFormat();
	bool ftrace_header_parsed = false;
	FtracePageHeaderSpec header_spec{};
	if (!page_header.empty()) {
	std::vector<FtraceEvent::Field> page_header_fields;
	ftrace_header_parsed = ParseFtraceEventBody(std::move(page_header), nullptr,
	&page_header_fields);
	header_spec = MakeFtracePageHeaderSpec(page_header_fields);
	}

	if (!ftrace_header_parsed) {
	PERFETTO_LOG("Failed to parse ftrace page header, using fallback layout");
	header_spec = GuessFtracePageHeaderSpec();
	}

	for (Event& event : events) {
	if (event.proto_field_id ==
	protos::pbzero::FtraceEvent::kGenericFieldNumber) {
	continue;
	}
	PERFETTO_DCHECK(event.name);
	PERFETTO_DCHECK(event.group);
	PERFETTO_DCHECK(event.proto_field_id);
	PERFETTO_DCHECK(!event.ftrace_event_id);

	std::string contents =
	ftrace_procfs->ReadEventFormat(event.group, event.name);
	FtraceEvent ftrace_event;
	if (contents.empty() \|\| !ParseFtraceEvent(contents, &ftrace_event)) {
	if (!strcmp(event.group, "ftrace") && !strcmp(event.name, "print")) {
	// On some "user" builds of Android <P the ftrace/print event is not
	// selinux-whitelisted. Thankfully this event is an always-on built-in
	// so we don't need to write to its 'enable' file. However we need to
	// know its binary layout to decode it, so we hardcode it.
	ftrace_event.id = 5; // Seems quite stable across kernels.
	ftrace_event.name = "print";
	// The only field we care about is:
	// field:char buf; offset:16; size:0; signed:0;
	ftrace_event.fields.emplace_back(
	FtraceEvent::Field{"char buf", 16, 0, 0});
	} else {
	continue;
	}
	}

	event.ftrace_event_id = ftrace_event.id;

	if (!common_fields_processed) {
	common_fields_end =
	MergeFields(ftrace_event.common_fields, &common_fields, event.name);
	common_fields_processed = true;
	}

	uint16_t fields_end =
	MergeFields(ftrace_event.fields, &event.fields, event.name);

	event.size = std::max<uint16_t>(fields_end, common_fields_end);
	}

	events.erase(std::remove_if(events.begin(), events.end(),
	[](const Event& event) {
	return event.proto_field_id == 0 \|\|
	event.ftrace_event_id == 0;
	}),
	events.end());

	auto table = std::unique_ptr<ProtoTranslationTable>(new ProtoTranslationTable(
	ftrace_procfs, events, std::move(common_fields), header_spec));
	return table;
	}

	ProtoTranslationTable::ProtoTranslationTable(
	const FtraceProcfs* ftrace_procfs,
	const std::vector<Event>& events,
	std::vector<Field> common_fields,
	FtracePageHeaderSpec ftrace_page_header_spec)
	: ftrace_procfs_(ftrace_procfs),
	events_(BuildEventsVector(events)),
	largest_id_(events_.size() - 1),
	common_fields_(std::move(common_fields)),
	ftrace_page_header_spec_(ftrace_page_header_spec) {
	for (const Event& event : events) {
	group_and_name_to_event_[GroupAndName(event.group, event.name)] =
	&events_.at(event.ftrace_event_id);
	name_to_events_[event.name].push_back(&events_.at(event.ftrace_event_id));
	group_to_events_[event.group].push_back(&events_.at(event.ftrace_event_id));
	}
	}

	const Event* ProtoTranslationTable::GetOrCreateEvent(
	const GroupAndName& group_and_name) {
	const Event* event = GetEvent(group_and_name);
	if (event)
	return event;
	// The ftrace event does not already exist so a new one will be created
	// by parsing the format file.
	std::string contents = ftrace_procfs_->ReadEventFormat(group_and_name.group(),
	group_and_name.name());
	if (contents.empty())
	return nullptr;
	FtraceEvent ftrace_event = {};
	ParseFtraceEvent(contents, &ftrace_event);

	// Ensure events vector is large enough
	if (ftrace_event.id > largest_id_) {
	events_.resize(ftrace_event.id + 1);
	largest_id_ = ftrace_event.id;
	}

	// Set known event variables
	Event* e = &events_.at(ftrace_event.id);
	e->ftrace_event_id = ftrace_event.id;
	e->proto_field_id = protos::pbzero::FtraceEvent::kGenericFieldNumber;
	e->name = InternString(group_and_name.name());
	e->group = InternString(group_and_name.group());

	// Calculate size of common fields.
	for (const FtraceEvent::Field& ftrace_field : ftrace_event.common_fields) {
	uint16_t field_end = ftrace_field.offset + ftrace_field.size;
	e->size = std::max(field_end, e->size);
	}

	// For every field in the ftrace event, make a field in the generic event.
	for (const FtraceEvent::Field& ftrace_field : ftrace_event.fields)
	e->size = std::max(CreateGenericEventField(ftrace_field, *e), e->size);

	group_and_name_to_event_[group_and_name] = &events_.at(e->ftrace_event_id);
	name_to_events_[e->name].push_back(&events_.at(e->ftrace_event_id));
	group_to_events_[e->group].push_back(&events_.at(e->ftrace_event_id));

	return e;
	};

	const char* ProtoTranslationTable::InternString(const std::string& str) {
	auto it_and_inserted = interned_strings_.insert(str);
	return it_and_inserted.first->c_str();
	};

	uint16_t ProtoTranslationTable::CreateGenericEventField(
	const FtraceEvent::Field& ftrace_field,
	Event& event) {
	uint16_t field_end = ftrace_field.offset + ftrace_field.size;
	std::string field_name = GetNameFromTypeAndName(ftrace_field.type_and_name);
	if (field_name.empty()) {
	PERFETTO_DLOG("Field: %s could not be added to the generic event.",
	ftrace_field.type_and_name.c_str());
	return field_end;
	}
	event.fields.emplace_back();
	Field* field = &event.fields.back();
	field->ftrace_name = InternString(field_name);
	if (!InferFtraceType(ftrace_field.type_and_name, ftrace_field.size,
	ftrace_field.is_signed, &field->ftrace_type)) {
	PERFETTO_DLOG(
	"Failed to infer ftrace field type for \"%s.%s\" (type:\"%s\" "
	"size:%d "
	"signed:%d)",
	event.name, field->ftrace_name, ftrace_field.type_and_name.c_str(),
	ftrace_field.size, ftrace_field.is_signed);
	event.fields.pop_back();
	return field_end;
	}
	SetProtoType(field->ftrace_type, &field->proto_field_type,
	&field->proto_field_id);
	field->ftrace_offset = ftrace_field.offset;
	field->ftrace_size = ftrace_field.size;
	// Proto type is set based on ftrace type so all fields should have a
	// translation strategy.
	bool success = SetTranslationStrategy(
	field->ftrace_type, field->proto_field_type, &field->strategy);
	PERFETTO_DCHECK(success);
	return field_end;
	}

	EventFilter::EventFilter() = default;
	EventFilter::~EventFilter() = default;

	void EventFilter::AddEnabledEvent(size_t ftrace_event_id) {
	if (ftrace_event_id >= enabled_ids_.size())
	enabled_ids_.resize(ftrace_event_id + 1);
	enabled_ids_[ftrace_event_id] = true;
	}

	void EventFilter::DisableEvent(size_t ftrace_event_id) {
	if (ftrace_event_id >= enabled_ids_.size())
	return;
	enabled_ids_[ftrace_event_id] = false;
	}

	bool EventFilter::IsEventEnabled(size_t ftrace_event_id) const {
	if (ftrace_event_id == 0 \|\| ftrace_event_id >= enabled_ids_.size())
	return false;
	return enabled_ids_[ftrace_event_id];
	}

	std::set<size_t> EventFilter::GetEnabledEvents() const {
	std::set<size_t> enabled;
	for (size_t i = 0; i < enabled_ids_.size(); i++) {
	if (enabled_ids_[i]) {
	enabled.insert(i);
	}
	}
	return enabled;
	}

	void EventFilter::EnableEventsFrom(const EventFilter& other) {
	size_t max_length = std::max(enabled_ids_.size(), other.enabled_ids_.size());
	enabled_ids_.resize(max_length);
	for (size_t i = 0; i < other.enabled_ids_.size(); i++) {
	if (other.enabled_ids_[i])
	enabled_ids_[i] = true;
	}
	}

	ProtoTranslationTable::~ProtoTranslationTable() = default;

	} // namespace perfetto