[src/trunk]: src/sys/kern Correct XXX comment in the ptrace(2) kernel code

[kamil <kamil%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/6c2d32a43d7f
branches:  trunk
changeset: 322278:6c2d32a43d7f
user:      kamil <kamil%NetBSD.org@localhost>
date:      Fri Apr 27 16:50:56 2018 +0000

description:
Correct XXX comment in the ptrace(2) kernel code

Explain I and D read/write operations and its history, removing dummy XXX
comments.

Sponsored by <The NetBSD Foundation>

diffstat:

 sys/kern/sys_ptrace_common.c |  17 +++++++++++++----
 1 files changed, 13 insertions(+), 4 deletions(-)

diffs (42 lines):

diff -r 6d7c6b2558ce -r 6c2d32a43d7f sys/kern/sys_ptrace_common.c
--- a/sys/kern/sys_ptrace_common.c      Fri Apr 27 16:32:03 2018 +0000
+++ b/sys/kern/sys_ptrace_common.c      Fri Apr 27 16:50:56 2018 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: sys_ptrace_common.c,v 1.36 2018/04/08 14:46:32 kamil Exp $     */
+/*     $NetBSD: sys_ptrace_common.c,v 1.37 2018/04/27 16:50:56 kamil Exp $     */
 
 /*-
  * Copyright (c) 2008, 2009 The NetBSD Foundation, Inc.
@@ -118,7 +118,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sys_ptrace_common.c,v 1.36 2018/04/08 14:46:32 kamil Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sys_ptrace_common.c,v 1.37 2018/04/27 16:50:56 kamil Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_ptrace.h"
@@ -1020,12 +1020,21 @@
                t->p_opptr = t->p_pptr;
                break;
 
-       case PT_WRITE_I:                /* XXX no separate I and D spaces */
+       /*
+        * The I and D separate address space has been inherited from PDP-11.
+        * The 16-bit UNIX started with a single address space per program,
+        * but was extended to two 16-bit (2 x 64kb) address spaces.
+        *
+        * We no longer maintain this feature in maintained architectures, but
+        * we keep the API for backward compatiblity. Currently the I and D
+        * operations are exactly the same and not distinguished in debuggers.
+        */
+       case PT_WRITE_I:
        case PT_WRITE_D:
                write = 1;
                tmp = data;
                /* FALLTHROUGH */
-       case PT_READ_I:                 /* XXX no separate I and D spaces */
+       case PT_READ_I:
        case PT_READ_D:
                piod.piod_addr = &tmp;
                piod.piod_len = sizeof(tmp);