var (
writeHeader = []byte{6 /* ANDROID_LOG_ERROR */, 'G', 'o', 0}
writePath = []byte("/dev/log/main\x00")
- writeFD uintptr
- writeBuf [1024]byte
- writePos int
+ 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) {
- // Log format: "<priority 1 byte><tag n bytes>\x00<message m bytes>\x00"
+ 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()
+ }
+ }
+
+ // 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.
- if writeFD == 0 {
- 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)
- }
- copy(writeBuf[:], writeHeader)
+ var hlen int
+ switch logger {
+ case logd:
+ hlen = writeLogdHeader()
+ case legacy:
+ hlen = len(writeHeader)
}
- dst := writeBuf[len(writeHeader):]
+
+ dst := writeBuf[hlen:]
for _, v := range b {
if v == 0 { // android logging won't print a zero byte
v = '0'
writePos++
if v == '\n' || writePos == len(dst)-1 {
dst[writePos] = 0
- write(writeFD, unsafe.Pointer(&writeBuf[0]), int32(len(writeHeader)+writePos))
+ write(writeFD, unsafe.Pointer(&writeBuf[0]), int32(hlen+writePos))
memclrBytes(dst)
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(uintptr(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 := time_now()
+ 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)
+}