Add support for executing the FreeBSD 1/i386 a.out binaries on amd64.

In particular:
- implement compat shims for old stat(2) variants and ogetdirentries(2);
- implement delivery of signals with ancient stack frame layout and
  corresponding sigreturn(2);
- implement old getpagesize(2);
- provide a user-mode trampoline and LDT call gate for lcall $7,$0;
- port a.out image activator and connect it to the build as a module
  on amd64.

The changes are hidden under COMPAT_43.

MFC after:   1 month

1 files changed, 16 insertions, 9 deletions

diff --git a/sys/kern/vfs_syscalls.c b/sys/kern/vfs_syscalls.c
index fe66591..649339b 100644
--- a/sys/kern/vfs_syscalls.c
+++ b/sys/kern/vfs_syscalls.c
@@ -3898,14 +3898,20 @@ struct ogetdirentries_args {
 };
 #endif
 int
-ogetdirentries(td, uap)
-	struct thread *td;
-	register struct ogetdirentries_args /* {
-		int fd;
-		char *buf;
-		u_int count;
-		long *basep;
-	} */ *uap;
+ogetdirentries(struct thread *td, struct ogetdirentries_args *uap)
+{
+	long loff;
+	int error;
+
+	error = kern_ogetdirentries(td, uap, &loff);
+	if (error == 0)
+		error = copyout(&loff, uap->basep, sizeof(long));
+	return (error);
+}
+
+int
+kern_ogetdirentries(struct thread *td, struct ogetdirentries_args *uap,
+    long *ploff)
 {
 	struct vnode *vp;
 	struct file *fp;
@@ -4024,9 +4030,10 @@ unionread:
 	}
 	VOP_UNLOCK(vp, 0);
 	VFS_UNLOCK_GIANT(vfslocked);
-	error = copyout(&loff, uap->basep, sizeof(long));
 	fdrop(fp, td);
 	td->td_retval[0] = uap->count - auio.uio_resid;
+	if (error == 0)
+		*ploff = loff;
 	return (error);
 }
 #endif /* COMPAT_43 */