Make forking of CloudABI processes work.

Just like FreeBSD+Capsicum, CloudABI uses process descriptors. Return
the file descriptor number to the parent process.

To the child process we both return a special value for the file
descriptor number (CLOUDABI_PROCESS_CHILD). We also return the thread ID
of the new thread in the copied process, so the threading library can
reinitialize itself.

Obtained from:	https://github.com/NuxiNL/freebsd

2 files changed, 21 insertions, 2 deletions

diff --git a/sys/amd64/cloudabi64/cloudabi64_sysvec.c b/sys/amd64/cloudabi64/cloudabi64_sysvec.c
index 96662a3..fc3f354 100644
--- a/sys/amd64/cloudabi64/cloudabi64_sysvec.c
+++ b/sys/amd64/cloudabi64/cloudabi64_sysvec.c
@@ -169,6 +169,16 @@ cloudabi64_set_syscall_retval(struct thread *td, int error)
 	}
 }
 
+static void
+cloudabi64_schedtail(struct thread *td)
+{
+	struct trapframe *frame = td->td_frame;
+
+	/* Initial register values for processes returning from fork. */
+	frame->tf_rax = CLOUDABI_PROCESS_CHILD;
+	frame->tf_rdx = td->td_tid;
+}
+
 static struct sysentvec cloudabi64_elf_sysvec = {
 	.sv_size		= CLOUDABI64_SYS_MAXSYSCALL,
 	.sv_table		= cloudabi64_sysent,
@@ -185,6 +195,7 @@ static struct sysentvec cloudabi64_elf_sysvec = {
 	.sv_set_syscall_retval	= cloudabi64_set_syscall_retval,
 	.sv_fetch_syscall_args	= cloudabi64_fetch_syscall_args,
 	.sv_syscallnames	= cloudabi64_syscallnames,
+	.sv_schedtail		= cloudabi64_schedtail,
 };
 
 INIT_SYSENTVEC(elf_sysvec, &cloudabi64_elf_sysvec);
diff --git a/sys/compat/cloudabi/cloudabi_proc.c b/sys/compat/cloudabi/cloudabi_proc.c
index dba1412..1f4418f 100644
--- a/sys/compat/cloudabi/cloudabi_proc.c
+++ b/sys/compat/cloudabi/cloudabi_proc.c
@@ -33,8 +33,10 @@ __FBSDID("$FreeBSD$");
 #include <sys/proc.h>
 #include <sys/signalvar.h>
 #include <sys/syscallsubr.h>
+#include <sys/unistd.h>
 
 #include <compat/cloudabi/cloudabi_proto.h>
+#include <compat/cloudabi/cloudabi_syscalldefs.h>
 
 int
 cloudabi_sys_proc_exec(struct thread *td,
@@ -65,9 +67,15 @@ int
 cloudabi_sys_proc_fork(struct thread *td,
     struct cloudabi_sys_proc_fork_args *uap)
 {
+	struct proc *p2;
+	int error, fd;
 
-	/* Not implemented. */
-	return (ENOSYS);
+	error = fork1(td, RFFDG | RFPROC | RFPROCDESC, 0, &p2, &fd, 0);
+	if (error != 0)
+		return (error);
+	/* Return the file descriptor to the parent process. */
+	td->td_retval[0] = fd;
+	return (0);
 }
 
 int