write_err_android.go

Documentation: runtime

     1  // Copyright 2014 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import "unsafe"
     8  
     9  var (
    10  	writeHeader = []byte{6 /* ANDROID_LOG_ERROR */, 'G', 'o', 0}
    11  	writePath   = []byte("/dev/log/main\x00")
    12  	writeLogd   = []byte("/dev/socket/logdw\x00")
    13  
    14  	// guarded by printlock/printunlock.
    15  	writeFD  uintptr
    16  	writeBuf [1024]byte
    17  	writePos int
    18  )
    19  
    20  // Prior to Android-L, logging was done through writes to /dev/log files implemented
    21  // in kernel ring buffers. In Android-L, those /dev/log files are no longer
    22  // accessible and logging is done through a centralized user-mode logger, logd.
    23  //
    24  // https://android.googlesource.com/platform/system/core/+/refs/tags/android-6.0.1_r78/liblog/logd_write.c
    25  type loggerType int32
    26  
    27  const (
    28  	unknown loggerType = iota
    29  	legacy
    30  	logd
    31  	// TODO(hakim): logging for emulator?
    32  )
    33  
    34  var logger loggerType
    35  
    36  func writeErr(b []byte) {
    37  	if len(b) == 0 {
    38  		return
    39  	}
    40  
    41  	if logger == unknown {
    42  		// Use logd if /dev/socket/logdw is available.
    43  		if v := uintptr(access(&writeLogd[0], 0x02 /* W_OK */)); v == 0 {
    44  			logger = logd
    45  			initLogd()
    46  		} else {
    47  			logger = legacy
    48  			initLegacy()
    49  		}
    50  	}
    51  
    52  	// Write to stderr for command-line programs,
    53  	// and optionally to SetCrashOutput file.
    54  	writeErrData(&b[0], int32(len(b)))
    55  
    56  	// Log format: "<header>\x00<message m bytes>\x00"
    57  	//
    58  	// <header>
    59  	//   In legacy mode: "<priority 1 byte><tag n bytes>".
    60  	//   In logd mode: "<android_log_header_t 11 bytes><priority 1 byte><tag n bytes>"
    61  	//
    62  	// The entire log needs to be delivered in a single syscall (the NDK
    63  	// does this with writev). Each log is its own line, so we need to
    64  	// buffer writes until we see a newline.
    65  	var hlen int
    66  	switch logger {
    67  	case logd:
    68  		hlen = writeLogdHeader()
    69  	case legacy:
    70  		hlen = len(writeHeader)
    71  	}
    72  
    73  	dst := writeBuf[hlen:]
    74  	for _, v := range b {
    75  		if v == 0 { // android logging won't print a zero byte
    76  			v = '0'
    77  		}
    78  		dst[writePos] = v
    79  		writePos++
    80  		if v == '\n' || writePos == len(dst)-1 {
    81  			dst[writePos] = 0
    82  			write(writeFD, unsafe.Pointer(&writeBuf[0]), int32(hlen+writePos))
    83  			clear(dst)
    84  			writePos = 0
    85  		}
    86  	}
    87  }
    88  
    89  func initLegacy() {
    90  	// In legacy mode, logs are written to /dev/log/main
    91  	writeFD = uintptr(open(&writePath[0], 0x1 /* O_WRONLY */, 0))
    92  	if writeFD == 0 {
    93  		// It is hard to do anything here. Write to stderr just
    94  		// in case user has root on device and has run
    95  		//	adb shell setprop log.redirect-stdio true
    96  		msg := []byte("runtime: cannot open /dev/log/main\x00")
    97  		write(2, unsafe.Pointer(&msg[0]), int32(len(msg)))
    98  		exit(2)
    99  	}
   100  
   101  	// Prepopulate the invariant header part.
   102  	copy(writeBuf[:len(writeHeader)], writeHeader)
   103  }
   104  
   105  // used in initLogdWrite but defined here to avoid heap allocation.
   106  var logdAddr sockaddr_un
   107  
   108  func initLogd() {
   109  	// In logd mode, logs are sent to the logd via a unix domain socket.
   110  	logdAddr.family = _AF_UNIX
   111  	copy(logdAddr.path[:], writeLogd)
   112  
   113  	// We are not using non-blocking I/O because writes taking this path
   114  	// are most likely triggered by panic, we cannot think of the advantage of
   115  	// non-blocking I/O for panic but see disadvantage (dropping panic message),
   116  	// and blocking I/O simplifies the code a lot.
   117  	fd := socket(_AF_UNIX, _SOCK_DGRAM|_O_CLOEXEC, 0)
   118  	if fd < 0 {
   119  		msg := []byte("runtime: cannot create a socket for logging\x00")
   120  		write(2, unsafe.Pointer(&msg[0]), int32(len(msg)))
   121  		exit(2)
   122  	}
   123  
   124  	errno := connect(fd, unsafe.Pointer(&logdAddr), int32(unsafe.Sizeof(logdAddr)))
   125  	if errno < 0 {
   126  		msg := []byte("runtime: cannot connect to /dev/socket/logdw\x00")
   127  		write(2, unsafe.Pointer(&msg[0]), int32(len(msg)))
   128  		// TODO(hakim): or should we just close fd and hope for better luck next time?
   129  		exit(2)
   130  	}
   131  	writeFD = uintptr(fd)
   132  
   133  	// Prepopulate invariant part of the header.
   134  	// The first 11 bytes will be populated later in writeLogdHeader.
   135  	copy(writeBuf[11:11+len(writeHeader)], writeHeader)
   136  }
   137  
   138  // writeLogdHeader populates the header and returns the length of the payload.
   139  func writeLogdHeader() int {
   140  	hdr := writeBuf[:11]
   141  
   142  	// The first 11 bytes of the header corresponds to android_log_header_t
   143  	// as defined in system/core/include/private/android_logger.h
   144  	//   hdr[0] log type id (unsigned char), defined in <log/log.h>
   145  	//   hdr[1:2] tid (uint16_t)
   146  	//   hdr[3:11] log_time defined in <log/log_read.h>
   147  	//      hdr[3:7] sec unsigned uint32, little endian.
   148  	//      hdr[7:11] nsec unsigned uint32, little endian.
   149  	hdr[0] = 0 // LOG_ID_MAIN
   150  	sec, nsec, _ := time_now()
   151  	packUint32(hdr[3:7], uint32(sec))
   152  	packUint32(hdr[7:11], uint32(nsec))
   153  
   154  	// TODO(hakim):  hdr[1:2] = gettid?
   155  
   156  	return 11 + len(writeHeader)
   157  }
   158  
   159  func packUint32(b []byte, v uint32) {
   160  	// little-endian.
   161  	b[0] = byte(v)
   162  	b[1] = byte(v >> 8)
   163  	b[2] = byte(v >> 16)
   164  	b[3] = byte(v >> 24)
   165  }
   166
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