frv: split ret_from_fork, simplify kernel_thread() a lot

Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/frv/kernel/Makefile

@@ -7,7 +7,7 @@ heads-$(CONFIG_MMU)		:= head-mmu-fr451.o
 
 extra-y:= head.o vmlinux.lds
 
-obj-y := $(heads-y) entry.o entry-table.o break.o switch_to.o kernel_thread.o \
+obj-y := $(heads-y) entry.o entry-table.o break.o switch_to.o \
 	 kernel_execve.o process.o traps.o ptrace.o signal.o dma.o \
 	 sys_frv.o time.o setup.o frv_ksyms.o \
 	 debug-stub.o irq.o sleep.o uaccess.o

arch/frv/kernel/entry.S

@@ -863,6 +863,14 @@ ret_from_fork:
 	setlos.p	#0,gr8
 	bra		__syscall_exit
 
+	.globl		ret_from_kernel_thread
+ret_from_kernel_thread:
+	lddi.p		@(gr28,#REG_GR(8)),gr20
+	call		schedule_tail
+	or.p		gr20,gr20,gr8
+	calll		@(gr21,gr0)
+	bra		sys_exit
+
 ###################################################################################################
 #
 # Return to user mode is not as complex as all this looks,

arch/frv/kernel/frv_ksyms.c

@@ -30,7 +30,6 @@ EXPORT_SYMBOL(ip_fast_csum);
 EXPORT_SYMBOL(local_irq_count);
 EXPORT_SYMBOL(local_bh_count);
 #endif
-EXPORT_SYMBOL(kernel_thread);
 
 EXPORT_SYMBOL(__res_bus_clock_speed_HZ);
 EXPORT_SYMBOL(__page_offset);

arch/frv/kernel/kernel_thread.S

-/* kernel_thread.S: kernel thread creation
- *
- * Copyright (C) 2003 Red Hat, Inc. All Rights Reserved.
- * Written by David Howells (dhowells@redhat.com)
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; either version
- * 2 of the License, or (at your option) any later version.
- */
-
-#include <linux/linkage.h>
-#include <linux/kern_levels.h>
-#include <asm/unistd.h>
-
-#define CLONE_VM	0x00000100	/* set if VM shared between processes */
-
-	.section .rodata
-kernel_thread_emsg:
-	.asciz	KERN_ERR "failed to create kernel thread: error=%d\n"
-
-	.text
-	.balign		4
-
-###############################################################################
-#
-# Create a kernel thread
-#
-# int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
-#
-###############################################################################
-	.globl		kernel_thread
-	.type		kernel_thread,@function
-kernel_thread:
-	or.p		gr8,gr0,gr4
-	or		gr9,gr0,gr5
-
-	# start by forking the current process, but with shared VM
-	setlos.p	#__NR_clone,gr7		; syscall number
-	ori		gr10,#CLONE_VM,gr8	; first syscall arg	[clone_flags]
-	sethi.p		#0xe4e4,gr9		; second syscall arg	[newsp]
-	setlo		#0xe4e4,gr9
-	setlos.p	#0,gr10			; third syscall arg	[parent_tidptr]
-	setlos		#0,gr11			; fourth syscall arg	[child_tidptr]
-	tira		gr0,#0
-	setlos.p	#4095,gr7
-	andcc		gr8,gr8,gr0,icc0
-	addcc.p		gr8,gr7,gr0,icc1
-	bnelr		icc0,#2
-	bc		icc1,#0,kernel_thread_error
-
-	# now invoke the work function
-	or		gr5,gr0,gr8
-	calll		@(gr4,gr0)
-
-	# and finally exit the thread
-	setlos		#__NR_exit,gr7		; syscall number
-	tira		gr0,#0
-
-kernel_thread_error:
-	subi		sp,#8,sp
-	movsg		lr,gr4
-	sti		gr8,@(sp,#0)
-	sti.p		gr4,@(sp,#4)
-
-	or		gr8,gr0,gr9
-	sethi.p		%hi(kernel_thread_emsg),gr8
-	setlo		%lo(kernel_thread_emsg),gr8
-
-	call		printk
-
-	ldi		@(sp,#4),gr4
-	ldi		@(sp,#0),gr8
-	subi		sp,#8,sp
-	jmpl		@(gr4,gr0)
-
-	.size		kernel_thread,.-kernel_thread

arch/frv/kernel/process.c

@@ -37,6 +37,7 @@
 #include "local.h"
 
 asmlinkage void ret_from_fork(void);
+asmlinkage void ret_from_kernel_thread(void);
 
 #include <asm/pgalloc.h>
 
@@ -172,29 +173,21 @@ int copy_thread(unsigned long clone_flags,
 		unsigned long usp, unsigned long topstk,
 		struct task_struct *p, struct pt_regs *regs)
 {
-	struct pt_regs *childregs0, *childregs, *regs0;
+	struct pt_regs *childregs;
 
-	regs0 = __kernel_frame0_ptr;
-	childregs0 = (struct pt_regs *)
+	childregs = (struct pt_regs *)
 		(task_stack_page(p) + THREAD_SIZE - FRV_FRAME0_SIZE);
-	childregs = childregs0;
 
 	/* set up the userspace frame (the only place that the USP is stored) */
-	*childregs0 = *regs0;
+	*childregs = *regs;
 
-	childregs0->gr8		= 0;
-	childregs0->sp		= usp;
-	childregs0->next_frame	= NULL;
+	childregs->sp		= usp;
+	childregs->next_frame	= NULL;
 
-	/* set up the return kernel frame if called from kernel_thread() */
-	if (regs != regs0) {
-		childregs--;
-		*childregs = *regs;
-		childregs->sp = (unsigned long) childregs0;
-		childregs->next_frame = childregs0;
-		childregs->gr15 = (unsigned long) task_thread_info(p);
-		childregs->gr29 = (unsigned long) p;
-	}
+	if (unlikely(!user_mode(regs)))
+		p->thread.pc = (unsigned long) ret_from_kernel_thread;
+	else
+		p->thread.pc = (unsigned long) ret_from_fork;
 
 	p->set_child_tid = p->clear_child_tid = NULL;
 
@@ -203,8 +196,7 @@ int copy_thread(unsigned long clone_flags,
 	p->thread.sp	 = (unsigned long) childregs;
 	p->thread.fp	 = 0;
 	p->thread.lr	 = 0;
-	p->thread.pc	 = (unsigned long) ret_from_fork;
-	p->thread.frame0 = childregs0;
+	p->thread.frame0 = childregs;
 
 	/* the new TLS pointer is passed in as arg #5 to sys_clone() */
 	if (clone_flags & CLONE_SETTLS)
@@ -347,3 +339,13 @@ int dump_fpu(struct pt_regs *regs, elf_fpregset_t *fpregs)
 	       sizeof(current->thread.user->f));
 	return 1;
 }
+
+int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
+{
+	struct pt_regs regs = {
+		.gr8 = (unsigned long)arg;
+		.gr9 = (unsigned long)fn;
+		.psr = PSR_S;
+	};
+	return do_fork(flags|CLONE_VM|CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
+}