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// Copyright 2022 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/android/thread_instruction_count.h"
#include "base/check_op.h"
#include "base/logging.h"
#include "base/no_destructor.h"
#include "base/numerics/safe_conversions.h"
#include "base/threading/thread_local_storage.h"
#include <linux/perf_event.h>
#include <sys/syscall.h>
#include <unistd.h>
namespace base {
namespace android {
namespace {
constexpr int kPerfFdOpenFailed = -1;
ThreadLocalStorage::Slot& InstructionCounterFdSlot() {
static NoDestructor<ThreadLocalStorage::Slot> fd_slot([](void* fd_ptr) {
int fd = checked_cast<int>(reinterpret_cast<intptr_t>(fd_ptr));
if (fd > 0)
close(fd);
});
return *fd_slot;
}
// Opens a new file descriptor that emits the value of
// PERF_COUNT_HW_INSTRUCTIONS in userspace (excluding kernel and hypervisor
// instructions) for the given |thread_id|, or 0 for the calling thread.
//
// Returns kPerfFdOpenFailed if opening the file descriptor failed.
int OpenInstructionCounterFdForThread(int thread_id) {
struct perf_event_attr pe = {0};
pe.type = PERF_TYPE_HARDWARE;
pe.size = sizeof(struct perf_event_attr);
pe.config = PERF_COUNT_HW_INSTRUCTIONS;
pe.exclude_kernel = 1;
pe.exclude_hv = 1;
long fd = syscall(__NR_perf_event_open, &pe, thread_id, /* cpu */ -1,
/* group_fd */ -1, /* flags */ 0);
if (fd < 0) {
PLOG(ERROR) << "perf_event_open: omitting instruction counters";
return kPerfFdOpenFailed;
}
return checked_cast<int>(fd);
}
// Retrieves the active perf counter FD for the current thread, performing
// lazy-initialization if necessary.
int InstructionCounterFdForCurrentThread() {
auto& slot = InstructionCounterFdSlot();
int fd = checked_cast<int>(reinterpret_cast<intptr_t>(slot.Get()));
if (fd == 0) {
fd = OpenInstructionCounterFdForThread(0);
slot.Set(reinterpret_cast<void*>(fd));
}
return fd;
}
} // namespace
// static
bool ThreadInstructionCount::IsSupported() {
return InstructionCounterFdForCurrentThread() > 0;
}
// static
ThreadInstructionCount ThreadInstructionCount::Now() {
DCHECK(IsSupported());
int fd = InstructionCounterFdForCurrentThread();
if (fd <= 0)
return ThreadInstructionCount();
uint64_t instructions = 0;
ssize_t bytes_read = read(fd, &instructions, sizeof(instructions));
CHECK_EQ(bytes_read, static_cast<ssize_t>(sizeof(instructions)))
<< "Short reads of small size from kernel memory is not expected. If "
"this fails, use HANDLE_EINTR.";
return ThreadInstructionCount(instructions);
}
} // namespace android
} // namespace base
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