[src/trunk]: src/sys/arch/m68k/m68k Restore comments for f_stackadj and reent...

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

details:   https://anonhg.NetBSD.org/src/rev/9c7795bfaf5f
branches:  trunk
changeset: 378714:9c7795bfaf5f
user:      tsutsui <tsutsui%NetBSD.org@localhost>
date:      Sat Apr 24 16:14:08 2021 +0000

description:
Restore comments for f_stackadj and reenter_syscall().

Taken from sys/compat/linux/arch/m68k/linux_machdep.c which was
originally implemented to use reenter_syscall() for sigreturn of
Linux binaries.

diffstat:

 sys/arch/m68k/m68k/sig_machdep.c |  25 ++++++++++++++++++++++---
 1 files changed, 22 insertions(+), 3 deletions(-)

diffs (63 lines):

diff -r ab422d64e0bf -r 9c7795bfaf5f sys/arch/m68k/m68k/sig_machdep.c
--- a/sys/arch/m68k/m68k/sig_machdep.c  Sat Apr 24 15:38:10 2021 +0000
+++ b/sys/arch/m68k/m68k/sig_machdep.c  Sat Apr 24 16:14:08 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: sig_machdep.c,v 1.50 2018/11/27 14:09:54 maxv Exp $    */
+/*     $NetBSD: sig_machdep.c,v 1.51 2021/04/24 16:14:08 tsutsui Exp $ */
 
 /*
  * Copyright (c) 1988 University of Utah.
@@ -40,7 +40,7 @@
 #include "opt_m68k_arch.h"
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sig_machdep.c,v 1.50 2018/11/27 14:09:54 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sig_machdep.c,v 1.51 2021/04/24 16:14:08 tsutsui Exp $");
 
 #define __M68K_SIGNAL_PRIVATE
 
@@ -236,7 +236,16 @@ cpu_getmcontext(struct lwp *l, mcontext_
                (void)memcpy(&mcp->__mc_pad.__mc_frame.__mcf_exframe,
                    &frame->F_u, (size_t)exframesize[format]);
 
-               /* Leave indicators, see above. */
+               /*
+                * Leave indicators that we need to clean up the kernel
+                * stack.  We do this by setting the "pad word" above the
+                * hardware stack frame to the amount the stack must be
+                * adjusted by.
+                *
+                * N.B. we increment rather than just set f_stackadj in
+                * case we are called from syscall when processing a
+                * sigreturn.  In that case, f_stackadj may be non-zero.
+                */
                frame->f_stackadj += exframesize[format];
                frame->f_format = frame->f_vector = 0;
        }
@@ -303,16 +312,26 @@ cpu_setmcontext(struct lwp *l, const mco
                        return (EINVAL);
 
                if (frame->f_stackadj == 0) {
+                       /*
+                        * Extra stack space is required but not allocated.
+                        * Allocate and re-enter syscall().
+                        */
                        reenter_syscall(frame, sz);
                        /* NOTREACHED */
                }
 
 #ifdef DIAGNOSTIC
+               /* reenter_syscall() should adjust stack for the extra frame. */
                if (sz != frame->f_stackadj)
                        panic("cpu_setmcontext: %d != %d",
                            sz, frame->f_stackadj);
 #endif
 
+               /*
+                * Restore long stack frames.  Note that we do not copy
+                * back the saved SR or PC, they were picked up below from
+                * the sigcontext structure.
+                */
                frame->f_format = format;
                frame->f_vector = mcp->__mc_pad.__mc_frame.__mcf_vector;
                (void)memcpy(&frame->F_u,