syscall: fix Exec on solaris

The test added for issue #18146 exposed a long-existing bug in the
Solaris port; notably, that syscall.Exec uses RawSyscall -- which is not
actually functional for the Solaris port (intentionally) and only exists
as a placebo to satisfy build requirements.

Call syscall.execve instead for Solaris.

Fixes #20832

Change-Id: I327d863f4bbbbbb6e5ecf66b82152c4030825d09
Reviewed-on: https://go-review.googlesource.com/47032
Run-TryBot: Shawn Walker-Salas <shawn.walker@oracle.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/syscall/exec_solaris.go

@@ -41,6 +41,11 @@ func setuid(uid uintptr) (err Errno)
 func setpgid(pid uintptr, pgid uintptr) (err Errno)
 func write1(fd uintptr, buf uintptr, nbyte uintptr) (n uintptr, err Errno)
 
+// syscall defines this global on our behalf to avoid a build dependency on other platforms
+func init() {
+	execveSolaris = execve
+}
+
 // Fork, dup fd onto 0..len(fd), and exec(argv0, argvv, envv) in child.
 // If a dup or exec fails, write the errno error to pipe.
 // (Pipe is close-on-exec so if exec succeeds, it will be closed.)

src/syscall/exec_unix.go

@@ -246,6 +246,10 @@ func StartProcess(argv0 string, argv []string, attr *ProcAttr) (pid int, handle
 func runtime_BeforeExec()
 func runtime_AfterExec()
 
+// execveSolaris is non-nil on Solaris, set to execve in exec_solaris.go; this
+// avoids a build dependency for other platforms.
+var execveSolaris func(path uintptr, argv uintptr, envp uintptr) (err Errno)
+
 // Exec invokes the execve(2) system call.
 func Exec(argv0 string, argv []string, envv []string) (err error) {
 	argv0p, err := BytePtrFromString(argv0)
@@ -261,10 +265,20 @@ func Exec(argv0 string, argv []string, envv []string) (err error) {
 		return err
 	}
 	runtime_BeforeExec()
-	_, _, err1 := RawSyscall(SYS_EXECVE,
+
+	var err1 Errno
+	if runtime.GOOS == "solaris" {
+		// RawSyscall should never be used on Solaris.
+		err1 = execveSolaris(
+			uintptr(unsafe.Pointer(argv0p)),
+			uintptr(unsafe.Pointer(&argvp[0])),
+			uintptr(unsafe.Pointer(&envvp[0])))
+	} else {
+		_, _, err1 = RawSyscall(SYS_EXECVE,
 			uintptr(unsafe.Pointer(argv0p)),
 			uintptr(unsafe.Pointer(&argvp[0])),
 			uintptr(unsafe.Pointer(&envvp[0])))
+	}
 	runtime_AfterExec()
-	return Errno(err1)
+	return err1
 }