runtime: support panic/print logging in android-L.

In android-L, logging is done through the logd daemon.
If logd daemon is available, send logging to logd.
Otherwise, fallback to the legacy mechanism (/dev/log files).

This change adds access/socket/connect calls to interact with the logd.

Fixes golang/go#9398.

Change-Id: I3c52b81b451f5862107d7c675f799fc85548486d
Reviewed-on: https://go-review.googlesource.com/3350Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/runtime/defs_linux_arm.go

@@ -65,7 +65,7 @@ const (
 	_ITIMER_PROF    = 0x2
 	_ITIMER_VIRTUAL = 0x1
 	_O_RDONLY       = 0
-	_O_CLOEXEC      = 02000000
+	_O_CLOEXEC      = 0x80000
 
 	_EPOLLIN       = 0x1
 	_EPOLLOUT      = 0x4
@@ -77,6 +77,10 @@ const (
 	_EPOLL_CTL_ADD = 0x1
 	_EPOLL_CTL_DEL = 0x2
 	_EPOLL_CTL_MOD = 0x3
+
+	_AF_UNIX    = 0x1
+	_F_SETFL    = 0x4
+	_SOCK_DGRAM = 0x2
 )
 
 type timespec struct {
@@ -166,3 +170,8 @@ type epollevent struct {
 	_pad   uint32
 	data   [8]byte // to match amd64
 }
+
+type sockaddr_un struct {
+	family uint16
+	path   [108]byte
+}

src/runtime/print1_write_android.go

@@ -9,29 +9,60 @@ import "unsafe"
 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'
@@ -40,9 +71,87 @@ func writeErr(b []byte) {
 		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)
+}

src/runtime/stubs_android.go

+package runtime
+
+import "unsafe"
+
+//go:noescape
+func access(name *byte, mode int32) int32
+
+func connect(fd uintptr, addr unsafe.Pointer, len int32) int32
+
+func socket(domain int32, typ int32, prot int32) int32

src/runtime/sys_linux_arm.s

@@ -45,6 +45,9 @@
 #define SYS_epoll_wait (SYS_BASE + 252)
 #define SYS_epoll_create1 (SYS_BASE + 357)
 #define SYS_fcntl (SYS_BASE + 55)
+#define SYS_access (SYS_BASE + 33)
+#define SYS_connect (SYS_BASE + 283)
+#define SYS_socket (SYS_BASE + 281)
 
 #define ARM_BASE (SYS_BASE + 0x0f0000)
 
@@ -471,3 +474,29 @@ TEXT runtime·closeonexec(SB),NOSPLIT,$0
 TEXT runtime·read_tls_fallback(SB),NOSPLIT,$-4
 	MOVW	$0xffff0fe0, R0
 	B	(R0)
+
+TEXT runtime·access(SB),NOSPLIT,$0
+	MOVW	0(FP), R0
+	MOVW	4(FP), R1
+	MOVW	$SYS_access, R7
+	SWI	$0
+	MOVW	R0, ret+8(FP)
+	RET
+
+TEXT runtime·connect(SB),NOSPLIT,$0
+	MOVW	0(FP), R0
+	MOVW	4(FP), R1
+	MOVW	8(FP), R2
+	MOVW	$SYS_connect, R7
+	SWI	$0
+	MOVW	R0, ret+12(FP)
+	RET
+
+TEXT runtime·socket(SB),NOSPLIT,$0
+	MOVW	0(FP), R0
+	MOVW	4(FP), R1
+	MOVW	8(FP), R2
+	MOVW	$SYS_socket, R7
+	SWI	$0
+	MOVW	R0, ret+12(FP)
+	RET