mn10300: split ret_from_fork, simplify kernel_thread()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/mn10300/kernel/Makefile

@@ -7,7 +7,7 @@ fpu-obj-y := fpu-nofpu.o fpu-nofpu-low.o
 fpu-obj-$(CONFIG_FPU) := fpu.o fpu-low.o
 
 obj-y   := process.o signal.o entry.o traps.o irq.o \
-	   ptrace.o setup.o time.o sys_mn10300.o io.o kthread.o \
+	   ptrace.o setup.o time.o sys_mn10300.o io.o \
 	   switch_to.o mn10300_ksyms.o kernel_execve.o $(fpu-obj-y) \
 	   csrc-mn10300.o cevt-mn10300.o
 

arch/mn10300/kernel/entry.S

@@ -55,6 +55,13 @@ ENTRY(ret_from_fork)
 	mov	d0,(REG_D0,fp)
 	jmp	syscall_exit
 
+ENTRY(ret_from_kernel_thread)
+	call	schedule_tail[],0
+	mov	(REG_D0,fp),d0
+	mov	(REG_A0,fp),a0
+	calls	(a0)
+	jmp	sys_exit
+
 ###############################################################################
 #
 # system call handler

arch/mn10300/kernel/internal.h

@@ -14,15 +14,11 @@
 struct clocksource;
 struct clock_event_device;
 
-/*
- * kthread.S
- */
-extern int kernel_thread_helper(int);
-
 /*
  * entry.S
  */
 extern void ret_from_fork(struct task_struct *) __attribute__((noreturn));
+extern void ret_from_kernel_thread(struct task_struct *) __attribute__((noreturn));
 
 /*
  * smp-low.S

arch/mn10300/kernel/kthread.S

-/* MN10300 Kernel thread trampoline function
- *
- * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
- * Written by Mark Salter (msalter@redhat.com)
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public Licence
- * as published by the Free Software Foundation; either version
- * 2 of the Licence, or (at your option) any later version.
- */
-	.text
-
-###############################################################################
-#
-# kernel_thread_helper - trampoline for kernel_thread()
-#
-# On entry:
-#   A2 = address of function to call
-#   D2 = function argument
-#
-###############################################################################
-	.globl	kernel_thread_helper
-	.type	kernel_thread_helper,@function
-kernel_thread_helper:
-	mov	do_exit,d1
-	mov	d1,(sp)
-	mov	d1,mdr
-	mov	d2,d0
-	jmp	(a2)
-
-	.size	kernel_thread_helper,.-kernel_thread_helper

arch/mn10300/kernel/process.c

@@ -166,13 +166,11 @@ void show_regs(struct pt_regs *regs)
  */
 int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
 {
-	struct pt_regs regs;
+	struct pt_regs regs = {
+		.a0 = (unsigned long) fn;
+		.d0 = (unsigned long) arg;
+	};
 
-	memset(&regs, 0, sizeof(regs));
-
-	regs.a2 = (unsigned long) fn;
-	regs.d2 = (unsigned long) arg;
-	regs.pc = (unsigned long) kernel_thread_helper;
 	local_save_flags(regs.epsw);
 	regs.epsw |= EPSW_IE | EPSW_IM_7;
 
@@ -180,7 +178,6 @@ int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
 	return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs, 0,
 		       NULL, NULL);
 }
-EXPORT_SYMBOL(kernel_thread);
 
 /*
  * free current thread data structures etc..
@@ -227,49 +224,36 @@ int copy_thread(unsigned long clone_flags,
 		struct task_struct *p, struct pt_regs *kregs)
 {
 	struct thread_info *ti = task_thread_info(p);
-	struct pt_regs *c_uregs, *c_kregs, *uregs;
+	struct pt_regs *c_regs;
 	unsigned long c_ksp;
 
-	uregs = current->thread.uregs;
-
 	c_ksp = (unsigned long) task_stack_page(p) + THREAD_SIZE;
 
 	/* allocate the userspace exception frame and set it up */
 	c_ksp -= sizeof(struct pt_regs);
-	c_uregs = (struct pt_regs *) c_ksp;
+	c_regs = (struct pt_regs *) c_ksp;
 
-	p->thread.uregs = c_uregs;
-	*c_uregs = *uregs;
-	c_uregs->sp = c_usp;
-	c_uregs->epsw &= ~EPSW_FE; /* my FPU */
+	p->thread.uregs = c_regs;
+	*c_regs = *kregs;
+	c_regs->sp = c_usp;
+	c_regs->epsw &= ~EPSW_FE; /* my FPU */
 
 	c_ksp -= 12; /* allocate function call ABI slack */
 
 	/* the new TLS pointer is passed in as arg #5 to sys_clone() */
 	if (clone_flags & CLONE_SETTLS)
-		c_uregs->e2 = current_frame()->d3;
-
-	/* set up the return kernel frame if called from kernel_thread() */
-	c_kregs = c_uregs;
-	if (kregs != uregs) {
-		c_ksp -= sizeof(struct pt_regs);
-		c_kregs = (struct pt_regs *) c_ksp;
-		*c_kregs = *kregs;
-		c_kregs->sp = c_usp;
-		c_kregs->next = c_uregs;
-#ifdef CONFIG_MN10300_CURRENT_IN_E2
-		c_kregs->e2 = (unsigned long) p; /* current */
-#endif
+		c_regs->e2 = current_frame()->d3;
 
-		c_ksp -= 12; /* allocate function call ABI slack */
-	}
+	if (unlikely(!user_mode(kregs)))
+		p->thread.pc	= (unsigned long) ret_from_kernel_thread;
+	else
+		p->thread.pc	= (unsigned long) ret_from_fork;
 
 	/* set up things up so the scheduler can start the new task */
-	ti->frame	= c_kregs;
-	p->thread.a3	= (unsigned long) c_kregs;
+	ti->frame	= c_regs;
+	p->thread.a3	= (unsigned long) c_regs;
 	p->thread.sp	= c_ksp;
-	p->thread.pc	= (unsigned long) ret_from_fork;
-	p->thread.wchan	= (unsigned long) ret_from_fork;
+	p->thread.wchan	= p->thread.pc;
 	p->thread.usp	= c_usp;
 
 	return 0;