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Source file src/runtime/write_err_android.go

Documentation: runtime

  // Copyright 2014 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package runtime
  
  import "unsafe"
  
  var (
  	writeHeader = []byte{6 /* ANDROID_LOG_ERROR */, 'G', 'o', 0}
  	writePath   = []byte("/dev/log/main\x00")
  	writeLogd   = []byte("/dev/socket/logdw\x00")
  
  	// guarded by printlock/printunlock.
  	writeFD  uintptr
  	writeBuf [1024]byte
  	writePos int
  )
  
  // Prior to Android-L, logging was done through writes to /dev/log files implemented
  // in kernel ring buffers. In Android-L, those /dev/log files are no longer
  // accessible and logging is done through a centralized user-mode logger, logd.
  //
  // https://android.googlesource.com/platform/system/core/+/master/liblog/logd_write.c
  type loggerType int32
  
  const (
  	unknown loggerType = iota
  	legacy
  	logd
  	// TODO(hakim): logging for emulator?
  )
  
  var logger loggerType
  
  func writeErr(b []byte) {
  	if logger == unknown {
  		// Use logd if /dev/socket/logdw is available.
  		if v := uintptr(access(&writeLogd[0], 0x02 /* W_OK */)); v == 0 {
  			logger = logd
  			initLogd()
  		} else {
  			logger = legacy
  			initLegacy()
  		}
  	}
  
  	// Write to stderr for command-line programs.
  	write(2, unsafe.Pointer(&b[0]), int32(len(b)))
  
  	// Log format: "<header>\x00<message m bytes>\x00"
  	//
  	// <header>
  	//   In legacy mode: "<priority 1 byte><tag n bytes>".
  	//   In logd mode: "<android_log_header_t 11 bytes><priority 1 byte><tag n bytes>"
  	//
  	// The entire log needs to be delivered in a single syscall (the NDK
  	// does this with writev). Each log is its own line, so we need to
  	// buffer writes until we see a newline.
  	var hlen int
  	switch logger {
  	case logd:
  		hlen = writeLogdHeader()
  	case legacy:
  		hlen = len(writeHeader)
  	}
  
  	dst := writeBuf[hlen:]
  	for _, v := range b {
  		if v == 0 { // android logging won't print a zero byte
  			v = '0'
  		}
  		dst[writePos] = v
  		writePos++
  		if v == '\n' || writePos == len(dst)-1 {
  			dst[writePos] = 0
  			write(writeFD, unsafe.Pointer(&writeBuf[0]), int32(hlen+writePos))
  			for i := range dst {
  				dst[i] = 0
  			}
  			writePos = 0
  		}
  	}
  }
  
  func initLegacy() {
  	// In legacy mode, logs are written to /dev/log/main
  	writeFD = uintptr(open(&writePath[0], 0x1 /* O_WRONLY */, 0))
  	if writeFD == 0 {
  		// It is hard to do anything here. Write to stderr just
  		// in case user has root on device and has run
  		//	adb shell setprop log.redirect-stdio true
  		msg := []byte("runtime: cannot open /dev/log/main\x00")
  		write(2, unsafe.Pointer(&msg[0]), int32(len(msg)))
  		exit(2)
  	}
  
  	// Prepopulate the invariant header part.
  	copy(writeBuf[:len(writeHeader)], writeHeader)
  }
  
  // used in initLogdWrite but defined here to avoid heap allocation.
  var logdAddr sockaddr_un
  
  func initLogd() {
  	// In logd mode, logs are sent to the logd via a unix domain socket.
  	logdAddr.family = _AF_UNIX
  	copy(logdAddr.path[:], writeLogd)
  
  	// We are not using non-blocking I/O because writes taking this path
  	// are most likely triggered by panic, we cannot think of the advantage of
  	// non-blocking I/O for panic but see disadvantage (dropping panic message),
  	// and blocking I/O simplifies the code a lot.
  	fd := socket(_AF_UNIX, _SOCK_DGRAM|_O_CLOEXEC, 0)
  	if fd < 0 {
  		msg := []byte("runtime: cannot create a socket for logging\x00")
  		write(2, unsafe.Pointer(&msg[0]), int32(len(msg)))
  		exit(2)
  	}
  
  	errno := connect(fd, unsafe.Pointer(&logdAddr), int32(unsafe.Sizeof(logdAddr)))
  	if errno < 0 {
  		msg := []byte("runtime: cannot connect to /dev/socket/logdw\x00")
  		write(2, unsafe.Pointer(&msg[0]), int32(len(msg)))
  		// TODO(hakim): or should we just close fd and hope for better luck next time?
  		exit(2)
  	}
  	writeFD = uintptr(fd)
  
  	// Prepopulate invariant part of the header.
  	// The first 11 bytes will be populated later in writeLogdHeader.
  	copy(writeBuf[11:11+len(writeHeader)], writeHeader)
  }
  
  // writeLogdHeader populates the header and returns the length of the payload.
  func writeLogdHeader() int {
  	hdr := writeBuf[:11]
  
  	// The first 11 bytes of the header corresponds to android_log_header_t
  	// as defined in system/core/include/private/android_logger.h
  	//   hdr[0] log type id (unsigned char), defined in <log/log.h>
  	//   hdr[1:2] tid (uint16_t)
  	//   hdr[3:11] log_time defined in <log/log_read.h>
  	//      hdr[3:7] sec unsigned uint32, little endian.
  	//      hdr[7:11] nsec unsigned uint32, little endian.
  	hdr[0] = 0 // LOG_ID_MAIN
  	sec, nsec := walltime()
  	packUint32(hdr[3:7], uint32(sec))
  	packUint32(hdr[7:11], uint32(nsec))
  
  	// TODO(hakim):  hdr[1:2] = gettid?
  
  	return 11 + len(writeHeader)
  }
  
  func packUint32(b []byte, v uint32) {
  	// little-endian.
  	b[0] = byte(v)
  	b[1] = byte(v >> 8)
  	b[2] = byte(v >> 16)
  	b[3] = byte(v >> 24)
  }
  

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