all: pretend to be linux/arm in baremetal targets

So far, we've pretended to be js/wasm in baremetal targets to make the
stdlib happy. Unfortunately, this has various problems because
syscall/js (a dependency of many stdlib packages) thinks it can do JS
calls, and emulating them gets quite hard with all changes to the
syscall/js packages in Go 1.12.

This commit does a few things:
  * It lets baremetal targets pretend to be linux/arm instead of
    js/wasm.
  * It lets the loader only select particular packages from the src
    overlay, instead of inserting them just before GOROOT. This makes it
    possible to pick which packages to overlay for a given target.
  * It adds a baremetal-only syscall package that stubs out almost all
    syscalls.

compiler/compiler.go

@@ -162,11 +162,11 @@ func (c *Compiler) selectGC() string {
 func (c *Compiler) Compile(mainPath string) error {
 	// Prefix the GOPATH with the system GOROOT, as GOROOT is already set to
 	// the TinyGo root.
-	gopath := c.GOPATH
-	if gopath == "" {
-		gopath = runtime.GOROOT()
+	overlayGopath := c.GOPATH
+	if overlayGopath == "" {
+		overlayGopath = runtime.GOROOT()
 	} else {
-		gopath = runtime.GOROOT() + string(filepath.ListSeparator) + gopath
+		overlayGopath = runtime.GOROOT() + string(filepath.ListSeparator) + overlayGopath
 	}
 
 	wd, err := os.Getwd()
@@ -177,13 +177,40 @@ func (c *Compiler) Compile(mainPath string) error {
 		Build: &build.Context{
 			GOARCH:      c.GOARCH,
 			GOOS:        c.GOOS,
-			GOROOT:      c.RootDir,
-			GOPATH:      gopath,
+			GOROOT:      runtime.GOROOT(),
+			GOPATH:      c.GOPATH,
 			CgoEnabled:  true,
 			UseAllFiles: false,
 			Compiler:    "gc", // must be one of the recognized compilers
 			BuildTags:   append([]string{"tinygo", "gc." + c.selectGC()}, c.BuildTags...),
 		},
+		OverlayBuild: &build.Context{
+			GOARCH:      c.GOARCH,
+			GOOS:        c.GOOS,
+			GOROOT:      c.RootDir,
+			GOPATH:      overlayGopath,
+			CgoEnabled:  true,
+			UseAllFiles: false,
+			Compiler:    "gc", // must be one of the recognized compilers
+			BuildTags:   append([]string{"tinygo", "gc." + c.selectGC()}, c.BuildTags...),
+		},
+		ShouldOverlay: func(path string) bool {
+			switch path {
+			case "machine", "os", "reflect", "runtime", "sync":
+				return true
+			default:
+				if strings.HasPrefix(path, "device/") || strings.HasPrefix(path, "examples/") {
+					return true
+				} else if path == "syscall" {
+					for _, tag := range c.BuildTags {
+						if tag == "avr" || tag == "cortexm" {
+							return true
+						}
+					}
+				}
+			}
+			return false
+		},
 		TypeChecker: types.Config{
 			Sizes: &StdSizes{
 				IntSize:  int64(c.targetData.TypeAllocSize(c.intType)),

loader/loader.go

@@ -14,13 +14,15 @@ import (
 
 // Program holds all packages and some metadata about the program as a whole.
 type Program struct {
-	Build       *build.Context
-	Packages    map[string]*Package
-	sorted      []*Package
-	fset        *token.FileSet
-	TypeChecker types.Config
-	Dir         string // current working directory (for error reporting)
-	CFlags      []string
+	Build         *build.Context
+	OverlayBuild  *build.Context
+	ShouldOverlay func(path string) bool
+	Packages      map[string]*Package
+	sorted        []*Package
+	fset          *token.FileSet
+	TypeChecker   types.Config
+	Dir           string // current working directory (for error reporting)
+	CFlags        []string
 }
 
 // Package holds a loaded package, its imports, and its parsed files.
@@ -42,7 +44,11 @@ func (p *Program) Import(path, srcDir string) (*Package, error) {
 	}
 
 	// Load this package.
-	buildPkg, err := p.Build.Import(path, srcDir, build.ImportComment)
+	ctx := p.Build
+	if p.ShouldOverlay(path) {
+		ctx = p.OverlayBuild
+	}
+	buildPkg, err := ctx.Import(path, srcDir, build.ImportComment)
 	if err != nil {
 		return nil, err
 	}

src/os/file_other.go

@@ -1,4 +1,4 @@
-// +build wasm
+// +build avr cortexm wasm
 
 package os
 

src/os/file_unix.go

@@ -1,4 +1,4 @@
-// +build darwin linux
+// +build darwin linux,!avr,!cortexm
 
 package os
 

src/runtime/arch_arm.go

@@ -1,3 +1,5 @@
+// +build arm,!avr,!cortexm
+
 package runtime
 
 const GOARCH = "arm"

src/runtime/arch_cortexm.go

@@ -1,4 +1,4 @@
-// +build tinygo.arm
+// +build cortexm
 
 package runtime
 

src/runtime/arch_wasm.go

@@ -1,4 +1,4 @@
-// +build wasm,!tinygo.arm,!avr
+// +build wasm
 
 package runtime
 

src/runtime/override_js.go

@@ -1,28 +0,0 @@
-// +build js,tinygo.arm avr
-
-package runtime
-
-// This file stubs out some external functions declared by the syscall/js
-// package. They cannot be used on microcontrollers.
-
-type js_ref uint64
-
-//go:linkname js_valueGet syscall/js.valueGet
-func js_valueGet(v js_ref, p string) js_ref {
-	return 0
-}
-
-//go:linkname js_valueNew syscall/js.valueNew
-func js_valueNew(v js_ref, args []js_ref) (js_ref, bool) {
-	return 0, true
-}
-
-//go:linkname js_valueCall syscall/js.valueCall
-func js_valueCall(v js_ref, m string, args []js_ref) (js_ref, bool) {
-	return 0, true
-}
-
-//go:linkname js_stringVal syscall/js.stringVal
-func js_stringVal(x string) js_ref {
-	return 0
-}

src/runtime/runtime_cortexm.go

@@ -1,4 +1,4 @@
-// +build tinygo.arm
+// +build cortexm
 
 package runtime
 

src/runtime/runtime_unix.go

@@ -1,4 +1,4 @@
-// +build darwin linux
+// +build darwin linux,!avr,!cortexm
 
 package runtime
 

src/runtime/runtime_wasm.go

@@ -1,4 +1,4 @@
-// +build wasm,!tinygo.arm,!avr
+// +build wasm
 
 package runtime
 

src/syscall/str.go

@@ -0,0 +1,24 @@
+// Copyright 2009 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 syscall
+
+func itoa(val int) string { // do it here rather than with fmt to avoid dependency
+	if val < 0 {
+		return "-" + uitoa(uint(-val))
+	}
+	return uitoa(uint(val))
+}
+
+func uitoa(val uint) string {
+	var buf [32]byte // big enough for int64
+	i := len(buf) - 1
+	for val >= 10 {
+		buf[i] = byte(val%10 + '0')
+		i--
+		val /= 10
+	}
+	buf[i] = byte(val + '0')
+	return string(buf[i:])
+}

src/syscall/syscall_baremetal.go

@@ -0,0 +1,148 @@
+package syscall
+
+// Most code here has been copied from the Go sources:
+//   https://github.com/golang/go/blob/go1.12/src/syscall/syscall_js.go
+// It has the following copyright note:
+//
+//     Copyright 2018 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.
+
+// An Errno is an unsigned number describing an error condition.
+// It implements the error interface. The zero Errno is by convention
+// a non-error, so code to convert from Errno to error should use:
+//      err = nil
+//      if errno != 0 {
+//              err = errno
+//      }
+type Errno uintptr
+
+func (e Errno) Error() string {
+        if 0 <= int(e) && int(e) < len(errorstr) {
+                s := errorstr[e]
+                if s != "" {
+                        return s
+                }
+        }
+        return "errno " + itoa(int(e))
+}
+
+func (e Errno) Temporary() bool {
+        return e == EINTR || e == EMFILE || e.Timeout()
+}
+
+func (e Errno) Timeout() bool {
+        return e == EAGAIN || e == EWOULDBLOCK || e == ETIMEDOUT
+}
+
+// A Signal is a number describing a process signal.
+// It implements the os.Signal interface.
+type Signal int
+
+const (
+	_ Signal = iota
+	SIGCHLD
+	SIGINT
+	SIGKILL
+	SIGTRAP
+	SIGQUIT
+	SIGTERM
+)
+
+// File system
+
+const (
+	Stdin  = 0
+	Stdout = 1
+	Stderr = 2
+)
+
+const (
+	O_RDONLY = 0
+	O_WRONLY = 1
+	O_RDWR   = 2
+
+	O_CREAT  = 0100
+	O_CREATE = O_CREAT
+	O_TRUNC  = 01000
+	O_APPEND = 02000
+	O_EXCL   = 0200
+	O_SYNC   = 010000
+
+	O_CLOEXEC = 0
+)
+
+func Getenv(key string) (value string, found bool) {
+	return "", false // stub
+}
+
+func Open(path string, mode int, perm uint32) (fd int, err error) {
+	return 0, ENOSYS
+}
+
+func Read(fd int, p []byte) (n int, err error) {
+	return 0, ENOSYS
+}
+
+func Seek(fd int, offset int64, whence int) (off int64, err error) {
+	return 0, ENOSYS
+}
+
+func Close(fd int) (err error) {
+	return ENOSYS
+}
+
+// Processes
+
+type WaitStatus uint32
+
+func (w WaitStatus) Exited() bool       { return false }
+func (w WaitStatus) ExitStatus() int    { return 0 }
+func (w WaitStatus) Signaled() bool     { return false }
+func (w WaitStatus) Signal() Signal     { return 0 }
+func (w WaitStatus) CoreDump() bool     { return false }
+func (w WaitStatus) Stopped() bool      { return false }
+func (w WaitStatus) Continued() bool    { return false }
+func (w WaitStatus) StopSignal() Signal { return 0 }
+func (w WaitStatus) TrapCause() int     { return 0 }
+
+// XXX made up
+type Rusage struct {
+	Utime Timeval
+	Stime Timeval
+}
+
+// XXX made up
+type ProcAttr struct {
+	Dir   string
+	Env   []string
+	Files []uintptr
+	Sys   *SysProcAttr
+}
+
+type SysProcAttr struct {
+}
+
+func Getegid() int                      { return 1 }
+func Geteuid() int                      { return 1 }
+func Getgid() int                       { return 1 }
+func Getgroups() ([]int, error)         { return []int{1}, nil }
+func Getppid() int                      { return 2 }
+func Getpid() int                       { return 3 }
+func Gettimeofday(tv *Timeval) error    { return ENOSYS }
+func Getuid() int                       { return 1 }
+func Kill(pid int, signum Signal) error { return ENOSYS }
+func Sendfile(outfd int, infd int, offset *int64, count int) (written int, err error) {
+	return 0, ENOSYS
+}
+func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle uintptr, err error) {
+	return 0, 0, ENOSYS
+}
+func Wait4(pid int, wstatus *WaitStatus, options int, rusage *Rusage) (wpid int, err error) {
+	return 0, ENOSYS
+}
+
+type Timeval struct {
+	Sec  int64
+	Usec int64
+}

src/syscall/tables_baremetal.go

@@ -0,0 +1,490 @@
+// Copyright 2013 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.
+
+// +build avr cortexm
+
+package syscall
+
+import "runtime"
+
+// TODO: generate with runtime/mknacl.sh, allow override with IRT.
+const (
+	sys_null                 = 1
+	sys_nameservice          = 2
+	sys_dup                  = 8
+	sys_dup2                 = 9
+	sys_open                 = 10
+	sys_close                = 11
+	sys_read                 = 12
+	sys_write                = 13
+	sys_lseek                = 14
+	sys_stat                 = 16
+	sys_fstat                = 17
+	sys_chmod                = 18
+	sys_isatty               = 19
+	sys_brk                  = 20
+	sys_mmap                 = 21
+	sys_munmap               = 22
+	sys_getdents             = 23
+	sys_mprotect             = 24
+	sys_list_mappings        = 25
+	sys_exit                 = 30
+	sys_getpid               = 31
+	sys_sched_yield          = 32
+	sys_sysconf              = 33
+	sys_gettimeofday         = 40
+	sys_clock                = 41
+	sys_nanosleep            = 42
+	sys_clock_getres         = 43
+	sys_clock_gettime        = 44
+	sys_mkdir                = 45
+	sys_rmdir                = 46
+	sys_chdir                = 47
+	sys_getcwd               = 48
+	sys_unlink               = 49
+	sys_imc_makeboundsock    = 60
+	sys_imc_accept           = 61
+	sys_imc_connect          = 62
+	sys_imc_sendmsg          = 63
+	sys_imc_recvmsg          = 64
+	sys_imc_mem_obj_create   = 65
+	sys_imc_socketpair       = 66
+	sys_mutex_create         = 70
+	sys_mutex_lock           = 71
+	sys_mutex_trylock        = 72
+	sys_mutex_unlock         = 73
+	sys_cond_create          = 74
+	sys_cond_wait            = 75
+	sys_cond_signal          = 76
+	sys_cond_broadcast       = 77
+	sys_cond_timed_wait_abs  = 79
+	sys_thread_create        = 80
+	sys_thread_exit          = 81
+	sys_tls_init             = 82
+	sys_thread_nice          = 83
+	sys_tls_get              = 84
+	sys_second_tls_set       = 85
+	sys_second_tls_get       = 86
+	sys_exception_handler    = 87
+	sys_exception_stack      = 88
+	sys_exception_clear_flag = 89
+	sys_sem_create           = 100
+	sys_sem_wait             = 101
+	sys_sem_post             = 102
+	sys_sem_get_value        = 103
+	sys_dyncode_create       = 104
+	sys_dyncode_modify       = 105
+	sys_dyncode_delete       = 106
+	sys_test_infoleak        = 109
+	sys_test_crash           = 110
+	sys_test_syscall_1       = 111
+	sys_test_syscall_2       = 112
+	sys_futex_wait_abs       = 120
+	sys_futex_wake           = 121
+	sys_pread                = 130
+	sys_pwrite               = 131
+	sys_truncate             = 140
+	sys_lstat                = 141
+	sys_link                 = 142
+	sys_rename               = 143
+	sys_symlink              = 144
+	sys_access               = 145
+	sys_readlink             = 146
+	sys_utimes               = 147
+	sys_get_random_bytes     = 150
+)
+
+// TODO: Auto-generate some day. (Hard-coded in binaries so not likely to change.)
+const (
+	// native_client/src/trusted/service_runtime/include/sys/errno.h
+	// The errors are mainly copied from Linux.
+	EPERM           Errno = 1       /* Operation not permitted */
+	ENOENT          Errno = 2       /* No such file or directory */
+	ESRCH           Errno = 3       /* No such process */
+	EINTR           Errno = 4       /* Interrupted system call */
+	EIO             Errno = 5       /* I/O error */
+	ENXIO           Errno = 6       /* No such device or address */
+	E2BIG           Errno = 7       /* Argument list too long */
+	ENOEXEC         Errno = 8       /* Exec format error */
+	EBADF           Errno = 9       /* Bad file number */
+	ECHILD          Errno = 10      /* No child processes */
+	EAGAIN          Errno = 11      /* Try again */
+	ENOMEM          Errno = 12      /* Out of memory */
+	EACCES          Errno = 13      /* Permission denied */
+	EFAULT          Errno = 14      /* Bad address */
+	EBUSY           Errno = 16      /* Device or resource busy */
+	EEXIST          Errno = 17      /* File exists */
+	EXDEV           Errno = 18      /* Cross-device link */
+	ENODEV          Errno = 19      /* No such device */
+	ENOTDIR         Errno = 20      /* Not a directory */
+	EISDIR          Errno = 21      /* Is a directory */
+	EINVAL          Errno = 22      /* Invalid argument */
+	ENFILE          Errno = 23      /* File table overflow */
+	EMFILE          Errno = 24      /* Too many open files */
+	ENOTTY          Errno = 25      /* Not a typewriter */
+	EFBIG           Errno = 27      /* File too large */
+	ENOSPC          Errno = 28      /* No space left on device */
+	ESPIPE          Errno = 29      /* Illegal seek */
+	EROFS           Errno = 30      /* Read-only file system */
+	EMLINK          Errno = 31      /* Too many links */
+	EPIPE           Errno = 32      /* Broken pipe */
+	ENAMETOOLONG    Errno = 36      /* File name too long */
+	ENOSYS          Errno = 38      /* Function not implemented */
+	EDQUOT          Errno = 122     /* Quota exceeded */
+	EDOM            Errno = 33      /* Math arg out of domain of func */
+	ERANGE          Errno = 34      /* Math result not representable */
+	EDEADLK         Errno = 35      /* Deadlock condition */
+	ENOLCK          Errno = 37      /* No record locks available */
+	ENOTEMPTY       Errno = 39      /* Directory not empty */
+	ELOOP           Errno = 40      /* Too many symbolic links */
+	ENOMSG          Errno = 42      /* No message of desired type */
+	EIDRM           Errno = 43      /* Identifier removed */
+	ECHRNG          Errno = 44      /* Channel number out of range */
+	EL2NSYNC        Errno = 45      /* Level 2 not synchronized */
+	EL3HLT          Errno = 46      /* Level 3 halted */
+	EL3RST          Errno = 47      /* Level 3 reset */
+	ELNRNG          Errno = 48      /* Link number out of range */
+	EUNATCH         Errno = 49      /* Protocol driver not attached */
+	ENOCSI          Errno = 50      /* No CSI structure available */
+	EL2HLT          Errno = 51      /* Level 2 halted */
+	EBADE           Errno = 52      /* Invalid exchange */
+	EBADR           Errno = 53      /* Invalid request descriptor */
+	EXFULL          Errno = 54      /* Exchange full */
+	ENOANO          Errno = 55      /* No anode */
+	EBADRQC         Errno = 56      /* Invalid request code */
+	EBADSLT         Errno = 57      /* Invalid slot */
+	EDEADLOCK       Errno = EDEADLK /* File locking deadlock error */
+	EBFONT          Errno = 59      /* Bad font file fmt */
+	ENOSTR          Errno = 60      /* Device not a stream */
+	ENODATA         Errno = 61      /* No data (for no delay io) */
+	ETIME           Errno = 62      /* Timer expired */
+	ENOSR           Errno = 63      /* Out of streams resources */
+	ENONET          Errno = 64      /* Machine is not on the network */
+	ENOPKG          Errno = 65      /* Package not installed */
+	EREMOTE         Errno = 66      /* The object is remote */
+	ENOLINK         Errno = 67      /* The link has been severed */
+	EADV            Errno = 68      /* Advertise error */
+	ESRMNT          Errno = 69      /* Srmount error */
+	ECOMM           Errno = 70      /* Communication error on send */
+	EPROTO          Errno = 71      /* Protocol error */
+	EMULTIHOP       Errno = 72      /* Multihop attempted */
+	EDOTDOT         Errno = 73      /* Cross mount point (not really error) */
+	EBADMSG         Errno = 74      /* Trying to read unreadable message */
+	EOVERFLOW       Errno = 75      /* Value too large for defined data type */
+	ENOTUNIQ        Errno = 76      /* Given log. name not unique */
+	EBADFD          Errno = 77      /* f.d. invalid for this operation */
+	EREMCHG         Errno = 78      /* Remote address changed */
+	ELIBACC         Errno = 79      /* Can't access a needed shared lib */
+	ELIBBAD         Errno = 80      /* Accessing a corrupted shared lib */
+	ELIBSCN         Errno = 81      /* .lib section in a.out corrupted */
+	ELIBMAX         Errno = 82      /* Attempting to link in too many libs */
+	ELIBEXEC        Errno = 83      /* Attempting to exec a shared library */
+	EILSEQ          Errno = 84
+	EUSERS          Errno = 87
+	ENOTSOCK        Errno = 88  /* Socket operation on non-socket */
+	EDESTADDRREQ    Errno = 89  /* Destination address required */
+	EMSGSIZE        Errno = 90  /* Message too long */
+	EPROTOTYPE      Errno = 91  /* Protocol wrong type for socket */
+	ENOPROTOOPT     Errno = 92  /* Protocol not available */
+	EPROTONOSUPPORT Errno = 93  /* Unknown protocol */
+	ESOCKTNOSUPPORT Errno = 94  /* Socket type not supported */
+	EOPNOTSUPP      Errno = 95  /* Operation not supported on transport endpoint */
+	EPFNOSUPPORT    Errno = 96  /* Protocol family not supported */
+	EAFNOSUPPORT    Errno = 97  /* Address family not supported by protocol family */
+	EADDRINUSE      Errno = 98  /* Address already in use */
+	EADDRNOTAVAIL   Errno = 99  /* Address not available */
+	ENETDOWN        Errno = 100 /* Network interface is not configured */
+	ENETUNREACH     Errno = 101 /* Network is unreachable */
+	ENETRESET       Errno = 102
+	ECONNABORTED    Errno = 103 /* Connection aborted */
+	ECONNRESET      Errno = 104 /* Connection reset by peer */
+	ENOBUFS         Errno = 105 /* No buffer space available */
+	EISCONN         Errno = 106 /* Socket is already connected */
+	ENOTCONN        Errno = 107 /* Socket is not connected */
+	ESHUTDOWN       Errno = 108 /* Can't send after socket shutdown */
+	ETOOMANYREFS    Errno = 109
+	ETIMEDOUT       Errno = 110 /* Connection timed out */
+	ECONNREFUSED    Errno = 111 /* Connection refused */
+	EHOSTDOWN       Errno = 112 /* Host is down */
+	EHOSTUNREACH    Errno = 113 /* Host is unreachable */
+	EALREADY        Errno = 114 /* Socket already connected */
+	EINPROGRESS     Errno = 115 /* Connection already in progress */
+	ESTALE          Errno = 116
+	ENOTSUP         Errno = EOPNOTSUPP /* Not supported */
+	ENOMEDIUM       Errno = 123        /* No medium (in tape drive) */
+	ECANCELED       Errno = 125        /* Operation canceled. */
+	ELBIN           Errno = 2048       /* Inode is remote (not really error) */
+	EFTYPE          Errno = 2049       /* Inappropriate file type or format */
+	ENMFILE         Errno = 2050       /* No more files */
+	EPROCLIM        Errno = 2051
+	ENOSHARE        Errno = 2052   /* No such host or network path */
+	ECASECLASH      Errno = 2053   /* Filename exists with different case */
+	EWOULDBLOCK     Errno = EAGAIN /* Operation would block */
+)
+
+// TODO: Auto-generate some day. (Hard-coded in binaries so not likely to change.)
+var errorstr = [...]string{
+	EPERM:           "Operation not permitted",
+	ENOENT:          "No such file or directory",
+	ESRCH:           "No such process",
+	EINTR:           "Interrupted system call",
+	EIO:             "I/O error",
+	ENXIO:           "No such device or address",
+	E2BIG:           "Argument list too long",
+	ENOEXEC:         "Exec format error",
+	EBADF:           "Bad file number",
+	ECHILD:          "No child processes",
+	EAGAIN:          "Try again",
+	ENOMEM:          "Out of memory",
+	EACCES:          "Permission denied",
+	EFAULT:          "Bad address",
+	EBUSY:           "Device or resource busy",
+	EEXIST:          "File exists",
+	EXDEV:           "Cross-device link",
+	ENODEV:          "No such device",
+	ENOTDIR:         "Not a directory",
+	EISDIR:          "Is a directory",
+	EINVAL:          "Invalid argument",
+	ENFILE:          "File table overflow",
+	EMFILE:          "Too many open files",
+	ENOTTY:          "Not a typewriter",
+	EFBIG:           "File too large",
+	ENOSPC:          "No space left on device",
+	ESPIPE:          "Illegal seek",
+	EROFS:           "Read-only file system",
+	EMLINK:          "Too many links",
+	EPIPE:           "Broken pipe",
+	ENAMETOOLONG:    "File name too long",
+	ENOSYS:          "not implemented on " + runtime.GOOS,
+	EDQUOT:          "Quota exceeded",
+	EDOM:            "Math arg out of domain of func",
+	ERANGE:          "Math result not representable",
+	EDEADLK:         "Deadlock condition",
+	ENOLCK:          "No record locks available",
+	ENOTEMPTY:       "Directory not empty",
+	ELOOP:           "Too many symbolic links",
+	ENOMSG:          "No message of desired type",
+	EIDRM:           "Identifier removed",
+	ECHRNG:          "Channel number out of range",
+	EL2NSYNC:        "Level 2 not synchronized",
+	EL3HLT:          "Level 3 halted",
+	EL3RST:          "Level 3 reset",
+	ELNRNG:          "Link number out of range",
+	EUNATCH:         "Protocol driver not attached",
+	ENOCSI:          "No CSI structure available",
+	EL2HLT:          "Level 2 halted",
+	EBADE:           "Invalid exchange",
+	EBADR:           "Invalid request descriptor",
+	EXFULL:          "Exchange full",
+	ENOANO:          "No anode",
+	EBADRQC:         "Invalid request code",
+	EBADSLT:         "Invalid slot",
+	EBFONT:          "Bad font file fmt",
+	ENOSTR:          "Device not a stream",
+	ENODATA:         "No data (for no delay io)",
+	ETIME:           "Timer expired",
+	ENOSR:           "Out of streams resources",
+	ENONET:          "Machine is not on the network",
+	ENOPKG:          "Package not installed",
+	EREMOTE:         "The object is remote",
+	ENOLINK:         "The link has been severed",
+	EADV:            "Advertise error",
+	ESRMNT:          "Srmount error",
+	ECOMM:           "Communication error on send",
+	EPROTO:          "Protocol error",
+	EMULTIHOP:       "Multihop attempted",
+	EDOTDOT:         "Cross mount point (not really error)",
+	EBADMSG:         "Trying to read unreadable message",
+	EOVERFLOW:       "Value too large for defined data type",
+	ENOTUNIQ:        "Given log. name not unique",
+	EBADFD:          "f.d. invalid for this operation",
+	EREMCHG:         "Remote address changed",
+	ELIBACC:         "Can't access a needed shared lib",
+	ELIBBAD:         "Accessing a corrupted shared lib",
+	ELIBSCN:         ".lib section in a.out corrupted",
+	ELIBMAX:         "Attempting to link in too many libs",
+	ELIBEXEC:        "Attempting to exec a shared library",
+	ENOTSOCK:        "Socket operation on non-socket",
+	EDESTADDRREQ:    "Destination address required",
+	EMSGSIZE:        "Message too long",
+	EPROTOTYPE:      "Protocol wrong type for socket",
+	ENOPROTOOPT:     "Protocol not available",
+	EPROTONOSUPPORT: "Unknown protocol",
+	ESOCKTNOSUPPORT: "Socket type not supported",
+	EOPNOTSUPP:      "Operation not supported on transport endpoint",
+	EPFNOSUPPORT:    "Protocol family not supported",
+	EAFNOSUPPORT:    "Address family not supported by protocol family",
+	EADDRINUSE:      "Address already in use",
+	EADDRNOTAVAIL:   "Address not available",
+	ENETDOWN:        "Network interface is not configured",
+	ENETUNREACH:     "Network is unreachable",
+	ECONNABORTED:    "Connection aborted",
+	ECONNRESET:      "Connection reset by peer",
+	ENOBUFS:         "No buffer space available",
+	EISCONN:         "Socket is already connected",
+	ENOTCONN:        "Socket is not connected",
+	ESHUTDOWN:       "Can't send after socket shutdown",
+	ETIMEDOUT:       "Connection timed out",
+	ECONNREFUSED:    "Connection refused",
+	EHOSTDOWN:       "Host is down",
+	EHOSTUNREACH:    "Host is unreachable",
+	EALREADY:        "Socket already connected",
+	EINPROGRESS:     "Connection already in progress",
+	ENOMEDIUM:       "No medium (in tape drive)",
+	ECANCELED:       "Operation canceled.",
+	ELBIN:           "Inode is remote (not really error)",
+	EFTYPE:          "Inappropriate file type or format",
+	ENMFILE:         "No more files",
+	ENOSHARE:        "No such host or network path",
+	ECASECLASH:      "Filename exists with different case",
+}
+
+// Do the interface allocations only once for common
+// Errno values.
+var (
+	errEAGAIN error = EAGAIN
+	errEINVAL error = EINVAL
+	errENOENT error = ENOENT
+)
+
+// errnoErr returns common boxed Errno values, to prevent
+// allocations at runtime.
+func errnoErr(e Errno) error {
+	switch e {
+	case 0:
+		return nil
+	case EAGAIN:
+		return errEAGAIN
+	case EINVAL:
+		return errEINVAL
+	case ENOENT:
+		return errENOENT
+	}
+	return e
+}
+
+var errnoByCode = map[string]Errno{
+	"EPERM":           EPERM,
+	"ENOENT":          ENOENT,
+	"ESRCH":           ESRCH,
+	"EINTR":           EINTR,
+	"EIO":             EIO,
+	"ENXIO":           ENXIO,
+	"E2BIG":           E2BIG,
+	"ENOEXEC":         ENOEXEC,
+	"EBADF":           EBADF,
+	"ECHILD":          ECHILD,
+	"EAGAIN":          EAGAIN,
+	"ENOMEM":          ENOMEM,
+	"EACCES":          EACCES,
+	"EFAULT":          EFAULT,
+	"EBUSY":           EBUSY,
+	"EEXIST":          EEXIST,
+	"EXDEV":           EXDEV,
+	"ENODEV":          ENODEV,
+	"ENOTDIR":         ENOTDIR,
+	"EISDIR":          EISDIR,
+	"EINVAL":          EINVAL,
+	"ENFILE":          ENFILE,
+	"EMFILE":          EMFILE,
+	"ENOTTY":          ENOTTY,
+	"EFBIG":           EFBIG,
+	"ENOSPC":          ENOSPC,
+	"ESPIPE":          ESPIPE,
+	"EROFS":           EROFS,
+	"EMLINK":          EMLINK,
+	"EPIPE":           EPIPE,
+	"ENAMETOOLONG":    ENAMETOOLONG,
+	"ENOSYS":          ENOSYS,
+	"EDQUOT":          EDQUOT,
+	"EDOM":            EDOM,
+	"ERANGE":          ERANGE,
+	"EDEADLK":         EDEADLK,
+	"ENOLCK":          ENOLCK,
+	"ENOTEMPTY":       ENOTEMPTY,
+	"ELOOP":           ELOOP,
+	"ENOMSG":          ENOMSG,
+	"EIDRM":           EIDRM,
+	"ECHRNG":          ECHRNG,
+	"EL2NSYNC":        EL2NSYNC,
+	"EL3HLT":          EL3HLT,
+	"EL3RST":          EL3RST,
+	"ELNRNG":          ELNRNG,
+	"EUNATCH":         EUNATCH,
+	"ENOCSI":          ENOCSI,
+	"EL2HLT":          EL2HLT,
+	"EBADE":           EBADE,
+	"EBADR":           EBADR,
+	"EXFULL":          EXFULL,
+	"ENOANO":          ENOANO,
+	"EBADRQC":         EBADRQC,
+	"EBADSLT":         EBADSLT,
+	"EDEADLOCK":       EDEADLOCK,
+	"EBFONT":          EBFONT,
+	"ENOSTR":          ENOSTR,
+	"ENODATA":         ENODATA,
+	"ETIME":           ETIME,
+	"ENOSR":           ENOSR,
+	"ENONET":          ENONET,
+	"ENOPKG":          ENOPKG,
+	"EREMOTE":         EREMOTE,
+	"ENOLINK":         ENOLINK,
+	"EADV":            EADV,
+	"ESRMNT":          ESRMNT,
+	"ECOMM":           ECOMM,
+	"EPROTO":          EPROTO,
+	"EMULTIHOP":       EMULTIHOP,
+	"EDOTDOT":         EDOTDOT,
+	"EBADMSG":         EBADMSG,
+	"EOVERFLOW":       EOVERFLOW,
+	"ENOTUNIQ":        ENOTUNIQ,
+	"EBADFD":          EBADFD,
+	"EREMCHG":         EREMCHG,
+	"ELIBACC":         ELIBACC,
+	"ELIBBAD":         ELIBBAD,
+	"ELIBSCN":         ELIBSCN,
+	"ELIBMAX":         ELIBMAX,
+	"ELIBEXEC":        ELIBEXEC,
+	"EILSEQ":          EILSEQ,
+	"EUSERS":          EUSERS,
+	"ENOTSOCK":        ENOTSOCK,
+	"EDESTADDRREQ":    EDESTADDRREQ,
+	"EMSGSIZE":        EMSGSIZE,
+	"EPROTOTYPE":      EPROTOTYPE,
+	"ENOPROTOOPT":     ENOPROTOOPT,
+	"EPROTONOSUPPORT": EPROTONOSUPPORT,
+	"ESOCKTNOSUPPORT": ESOCKTNOSUPPORT,
+	"EOPNOTSUPP":      EOPNOTSUPP,
+	"EPFNOSUPPORT":    EPFNOSUPPORT,
+	"EAFNOSUPPORT":    EAFNOSUPPORT,
+	"EADDRINUSE":      EADDRINUSE,
+	"EADDRNOTAVAIL":   EADDRNOTAVAIL,
+	"ENETDOWN":        ENETDOWN,
+	"ENETUNREACH":     ENETUNREACH,
+	"ENETRESET":       ENETRESET,
+	"ECONNABORTED":    ECONNABORTED,
+	"ECONNRESET":      ECONNRESET,
+	"ENOBUFS":         ENOBUFS,
+	"EISCONN":         EISCONN,
+	"ENOTCONN":        ENOTCONN,
+	"ESHUTDOWN":       ESHUTDOWN,
+	"ETOOMANYREFS":    ETOOMANYREFS,
+	"ETIMEDOUT":       ETIMEDOUT,
+	"ECONNREFUSED":    ECONNREFUSED,
+	"EHOSTDOWN":       EHOSTDOWN,
+	"EHOSTUNREACH":    EHOSTUNREACH,
+	"EALREADY":        EALREADY,
+	"EINPROGRESS":     EINPROGRESS,
+	"ESTALE":          ESTALE,
+	"ENOTSUP":         ENOTSUP,
+	"ENOMEDIUM":       ENOMEDIUM,
+	"ECANCELED":       ECANCELED,
+	"ELBIN":           ELBIN,
+	"EFTYPE":          EFTYPE,
+	"ENMFILE":         ENMFILE,
+	"EPROCLIM":        EPROCLIM,
+	"ENOSHARE":        ENOSHARE,
+	"ECASECLASH":      ECASECLASH,
+	"EWOULDBLOCK":     EWOULDBLOCK,
+}

src/unsafe/unsafe.go

@@ -1,3 +0,0 @@
-package unsafe
-
-// dummy

targets/avr.json

@@ -1,7 +1,7 @@
 {
-	"build-tags": ["avr", "js", "wasm"],
-	"goos": "js",
-	"goarch": "wasm",
+	"build-tags": ["avr", "linux", "arm"],
+	"goos": "linux",
+	"goarch": "arm",
 	"compiler": "avr-gcc",
 	"linker": "avr-gcc",
 	"ldflags": [

targets/cortex-m.json

@@ -1,7 +1,7 @@
 {
-	"build-tags": ["tinygo.arm", "js", "wasm"],
-	"goos": "js",
-	"goarch": "wasm",
+	"build-tags": ["cortexm", "linux", "arm"],
+	"goos": "linux",
+	"goarch": "arm",
 	"compiler": "clang-8",
 	"gc": "marksweep",
 	"linker": "arm-none-eabi-ld",