syscall: add Getexecname on Solaris for os.Executable

Change-Id: Icd77ccbfe6a31117a11effb949b5826950df75a9
Reviewed-on: https://go-review.googlesource.com/16550
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/syscall/syscall_solaris.go

@@ -509,6 +509,21 @@ func SendmsgN(fd int, p, oob []byte, to Sockaddr, flags int) (n int, err error)
 //sys	setsockopt(s int, level int, name int, val unsafe.Pointer, vallen uintptr) (err error) = libsocket.setsockopt
 //sys	recvfrom(fd int, p []byte, flags int, from *RawSockaddrAny, fromlen *_Socklen) (n int, err error) = libsocket.recvfrom
 //sys	recvmsg(s int, msg *Msghdr, flags int) (n int, err error) = libsocket.__xnet_recvmsg
+//sys	getexecname() (path unsafe.Pointer, err error) = libc.getexecname
+
+func Getexecname() (path string, err error) {
+	ptr, err := getexecname()
+	if err != nil {
+		return "", err
+	}
+	bytes := (*[1 << 29]byte)(ptr)[:]
+	for i, b := range bytes {
+		if b == 0 {
+			return string(bytes[:i]), nil
+		}
+	}
+	panic("unreachable")
+}
 
 func readlen(fd int, buf *byte, nbuf int) (n int, err error) {
 	r0, _, e1 := sysvicall6(uintptr(unsafe.Pointer(&libc_read)), 3, uintptr(fd), uintptr(unsafe.Pointer(buf)), uintptr(nbuf), 0, 0, 0)

src/syscall/zsyscall_solaris_amd64.go

@@ -89,6 +89,7 @@ import "unsafe"
 //go:cgo_import_dynamic libc_setsockopt setsockopt "libsocket.so"
 //go:cgo_import_dynamic libc_recvfrom recvfrom "libsocket.so"
 //go:cgo_import_dynamic libc___xnet_recvmsg __xnet_recvmsg "libsocket.so"
+//go:cgo_import_dynamic libc_getexecname getexecname "libc.so"
 
 //go:linkname libc_Getcwd libc_Getcwd
 //go:linkname libc_getgroups libc_getgroups
@@ -172,6 +173,7 @@ import "unsafe"
 //go:linkname libc_setsockopt libc_setsockopt
 //go:linkname libc_recvfrom libc_recvfrom
 //go:linkname libc___xnet_recvmsg libc___xnet_recvmsg
+//go:linkname libc_getexecname libc_getexecname
 
 type libcFunc uintptr
 
@@ -257,7 +259,8 @@ var (
 	libc_getsockname,
 	libc_setsockopt,
 	libc_recvfrom,
-	libc___xnet_recvmsg libcFunc
+	libc___xnet_recvmsg,
+	libc_getexecname libcFunc
 )
 
 func Getcwd(buf []byte) (n int, err error) {
@@ -1095,3 +1098,12 @@ func recvmsg(s int, msg *Msghdr, flags int) (n int, err error) {
 	}
 	return
 }
+
+func getexecname() (path unsafe.Pointer, err error) {
+	r0, _, e1 := sysvicall6(uintptr(unsafe.Pointer(&libc_getexecname)), 0, 0, 0, 0, 0, 0, 0)
+	path = unsafe.Pointer(r0)
+	if e1 != 0 {
+		err = errnoErr(e1)
+	}
+	return
+}