On Fri, Jun 18, 2021 at 3:34 PM Michael Schmitz <schmitzmic@xxxxxxxxx> wrote:
>
> Is your patch to copy_thread() to add the extra stack frame still needed?
So it's been a long time since I did any m68k assembly, but I think
the m68k patch for the PF_IO_WORKER thread case should look something
like the attached.
Note: my only m68k work was ever on the 68008, and used the Motorola
syntax, not the odd Sun assembler syntax, so my m68k asm skills really
aren't good.
Put another way: I'd be surprised if the attached patch actually
works, but I think it's fairly close. I tried to add comments to
explain the code at least a bit.
Hmm?
Linus
arch/m68k/kernel/entry.S | 10 ++++++++++
arch/m68k/kernel/process.c | 14 +++++++++-----
2 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
index 9dd76fbb7c6b..499f14d79640 100644
--- a/arch/m68k/kernel/entry.S
+++ b/arch/m68k/kernel/entry.S
@@ -119,6 +119,15 @@ ENTRY(ret_from_fork)
addql #4,%sp
jra ret_from_exception
+ | A kernel thread will jump here directly from resume,
+ | with the stack containing the full register state
+ | (pt_regs and switch_stack).
+ |
+ | The argument will be in d7, and the kernel function
+ | to call will be in a3.
+ |
+ | If the kernel function returns, we want to return
+ | to user space - it has done a kernel_execve().
ENTRY(ret_from_kernel_thread)
| a3 contains the kernel thread payload, d7 - its argument
movel %d1,%sp@-
@@ -126,6 +135,7 @@ ENTRY(ret_from_kernel_thread)
movel %d7,(%sp)
jsr %a3@
addql #4,%sp
+ RESTORE_SWITCH_STACK
jra ret_from_exception
#if defined(CONFIG_COLDFIRE) || !defined(CONFIG_MMU)
diff --git a/arch/m68k/kernel/process.c b/arch/m68k/kernel/process.c
index da83cc83e791..0705f14871a3 100644
--- a/arch/m68k/kernel/process.c
+++ b/arch/m68k/kernel/process.c
@@ -158,13 +158,17 @@ int copy_thread(unsigned long clone_flags, unsigned long usp, unsigned long arg,
p->thread.fs = get_fs().seg;
if (unlikely(p->flags & (PF_KTHREAD | PF_IO_WORKER))) {
- /* kernel thread */
- memset(frame, 0, sizeof(struct fork_frame));
+ struct switch_stack *kstp = &frame->sw - 1;
+
+ /* kernel thread - a kernel-side switch-stack and the full user fork_frame */
+ memset(kstp, 0, sizeof(struct switch_stack) + sizeof(struct fork_frame));
+
frame->regs.sr = PS_S;
- frame->sw.a3 = usp; /* function */
- frame->sw.d7 = arg;
- frame->sw.retpc = (unsigned long)ret_from_kernel_thread;
+ kstp->a3 = usp; /* function */
+ kstp->d7 = arg;
+ kstp->retpc = (unsigned long)ret_from_kernel_thread;
p->thread.usp = 0;
+ p->thread.ksp = (unsigned long)kstp;
return 0;
}
memcpy(frame, container_of(current_pt_regs(), struct fork_frame, regs),
