Make thread creation work for CloudABI processes.

Summary:
Remove the stub system call that was put in place during the system call
import and replace it by a target-dependent version stored in sys/amd64.
Initialize the thread in a way similar to cpu_set_upcall_kse(). We
provide the entry point with two arguments: the thread ID and the
argument pointer.

Test Plan:
Thread creation still seems to work, both for FreeBSD and CloudABI
binaries.

Reviewers: dchagin, mjg, kib

Reviewed By: kib

Subscribers: imp

Differential Revision: https://reviews.freebsd.org/D3110

sys/amd64/cloudabi64/cloudabi64_sysvec.c

@@ -50,6 +50,7 @@ __FBSDID("$FreeBSD$");
 
 #include <compat/cloudabi64/cloudabi64_syscall.h>
 #include <compat/cloudabi64/cloudabi64_syscalldefs.h>
+#include <compat/cloudabi64/cloudabi64_util.h>
 
 extern const char *cloudabi64_syscallnames[];
 extern struct sysent cloudabi64_sysent[];
@@ -179,6 +180,28 @@ cloudabi64_schedtail(struct thread *td)
 	frame->tf_rdx = td->td_tid;
 }
 
+void
+cloudabi64_thread_setregs(struct thread *td,
+    const cloudabi64_threadattr_t *attr)
+{
+	struct trapframe *frame;
+	stack_t stack;
+
+	/* Perform standard register initialization. */
+	stack.ss_sp = (void *)attr->stack;
+	stack.ss_size = attr->stack_size;
+	cpu_set_upcall_kse(td, (void *)attr->entry_point, NULL, &stack);
+
+	/*
+	 * Pass in the thread ID of the new thread and the argument
+	 * pointer provided by the parent thread in as arguments to the
+	 * entry point.
+	 */
+	frame = td->td_frame;
+	frame->tf_rdi = td->td_tid;
+	frame->tf_rsi = attr->argument;
+}
+
 static struct sysentvec cloudabi64_elf_sysvec = {
 	.sv_size		= CLOUDABI64_SYS_MAXSYSCALL,
 	.sv_table		= cloudabi64_sysent,

sys/compat/cloudabi64/cloudabi64_thread.c

@@ -26,14 +26,45 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include <sys/param.h>
+#include <sys/proc.h>
+#include <sys/systm.h>
+
 #include <compat/cloudabi64/cloudabi64_syscalldefs.h>
 #include <compat/cloudabi64/cloudabi64_proto.h>
+#include <compat/cloudabi64/cloudabi64_util.h>
+
+struct thread_create_args {
+	cloudabi64_threadattr_t attr;
+	lwpid_t tid;
+};
+
+static int
+initialize_thread(struct thread *td, void *thunk)
+{
+	struct thread_create_args *args = thunk;
+
+	/* Save the thread ID, so it can be returned. */
+	args->tid = td->td_tid;
+
+	/* Set up initial register contents. */
+	cloudabi64_thread_setregs(td, &args->attr);
+	return (0);
+}
 
 int
 cloudabi64_sys_thread_create(struct thread *td,
     struct cloudabi64_sys_thread_create_args *uap)
 {
+	struct thread_create_args args;
+	int error;
 
-	/* Not implemented. */
-	return (ENOSYS);
+	error = copyin(uap->attr, &args.attr, sizeof(args.attr));
+	if (error != 0)
+		return (error);
+	error = thread_create(td, NULL, initialize_thread, &args);
+	if (error != 0)
+		return (error);
+	td->td_retval[0] = args.tid;
+	return (0);
 }

sys/compat/cloudabi64/cloudabi64_util.h

@@ -0,0 +1,38 @@
+/*-
+ * Copyright (c) 2015 Nuxi, https://nuxi.nl/
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef _CLOUDABI64_UTIL_H_
+#define	_CLOUDABI64_UTIL_H_
+
+#include <compat/cloudabi64/cloudabi64_syscalldefs.h>
+
+struct thread;
+
+void	cloudabi64_thread_setregs(struct thread *,
+    const cloudabi64_threadattr_t *);
+
+#endif