powerpc: split ret_from_fork

... and get rid of in-kernel syscalls in kernel_thread()
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/powerpc/Kconfig

@@ -139,6 +139,7 @@ config PPC
 	select GENERIC_CLOCKEVENTS
 	select GENERIC_STRNCPY_FROM_USER
 	select GENERIC_STRNLEN_USER
+	select GENERIC_KERNEL_THREAD
 
 config EARLY_PRINTK
 	bool

arch/powerpc/include/asm/processor.h

@@ -74,9 +74,6 @@ struct task_struct;
 void start_thread(struct pt_regs *regs, unsigned long fdptr, unsigned long sp);
 void release_thread(struct task_struct *);
 
-/* Create a new kernel thread. */
-extern long kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
-
 /* Lazy FPU handling on uni-processor */
 extern struct task_struct *last_task_used_math;
 extern struct task_struct *last_task_used_altivec;

arch/powerpc/kernel/entry_32.S

@@ -435,6 +435,17 @@ ret_from_fork:
 	li	r3,0
 	b	ret_from_syscall
 
+	.globl	ret_from_kernel_thread
+ret_from_kernel_thread:
+	REST_NVGPRS(r1)
+	bl	schedule_tail
+	mtlr	r14
+	mr	r3,r15
+	PPC440EP_ERR42
+	blrl
+	li	r3,0
+	b	do_exit		# no return
+
 /* Traced system call support */
 syscall_dotrace:
 	SAVE_NVGPRS(r1)

arch/powerpc/kernel/entry_64.S

@@ -370,6 +370,16 @@ _GLOBAL(ret_from_fork)
 	li	r3,0
 	b	syscall_exit
 
+_GLOBAL(ret_from_kernel_thread)
+	bl	.schedule_tail
+	REST_NVGPRS(r1)
+	REST_GPR(2,r1)
+	mtlr	r14
+	mr	r3,r15
+	blrl
+	li	r3,0
+	b	.do_exit	# no return
+
 	.section	".toc","aw"
 DSCR_DEFAULT:
 	.tc dscr_default[TC],dscr_default

arch/powerpc/kernel/misc_32.S

@@ -663,39 +663,6 @@ _GLOBAL(abs)
 	sub	r3,r3,r4
 	blr
 
-/*
- * Create a kernel thread
- *   kernel_thread(fn, arg, flags)
- */
-_GLOBAL(kernel_thread)
-	stwu	r1,-16(r1)
-	stw	r30,8(r1)
-	stw	r31,12(r1)
-	mr	r30,r3		/* function */
-	mr	r31,r4		/* argument */
-	ori	r3,r5,CLONE_VM	/* flags */
-	oris	r3,r3,CLONE_UNTRACED>>16
-	li	r4,0		/* new sp (unused) */
-	li	r0,__NR_clone
-	sc
-	bns+	1f		/* did system call indicate error? */
-	neg	r3,r3		/* if so, make return code negative */
-1:	cmpwi	0,r3,0		/* parent or child? */
-	bne	2f		/* return if parent */
-	li	r0,0		/* make top-level stack frame */
-	stwu	r0,-16(r1)
-	mtlr	r30		/* fn addr in lr */
-	mr	r3,r31		/* load arg and call fn */
-	PPC440EP_ERR42
-	blrl
-	li	r0,__NR_exit	/* exit if function returns */
-	li	r3,0
-	sc
-2:	lwz	r30,8(r1)
-	lwz	r31,12(r1)
-	addi	r1,r1,16
-	blr
-
 #ifdef CONFIG_SMP
 _GLOBAL(start_secondary_resume)
 	/* Reset stack */

arch/powerpc/kernel/misc_64.S

@@ -406,40 +406,6 @@ _GLOBAL(scom970_write)
 #endif /* CONFIG_CPU_FREQ_PMAC64 || CONFIG_CPU_FREQ_MAPLE */
 
 
-/*
- * Create a kernel thread
- *   kernel_thread(fn, arg, flags)
- */
-_GLOBAL(kernel_thread)
-	std	r29,-24(r1)
-	std	r30,-16(r1)
-	stdu	r1,-STACK_FRAME_OVERHEAD(r1)
-	mr	r29,r3
-	mr	r30,r4
-	ori	r3,r5,CLONE_VM	/* flags */
-	oris	r3,r3,(CLONE_UNTRACED>>16)
-	li	r4,0		/* new sp (unused) */
-	li	r0,__NR_clone
-	sc
-	bns+	1f		/* did system call indicate error? */
-	neg	r3,r3		/* if so, make return code negative */
-1:	cmpdi	0,r3,0		/* parent or child? */
-	bne	2f		/* return if parent */
-	li	r0,0
-	stdu	r0,-STACK_FRAME_OVERHEAD(r1)
-	ld	r2,8(r29)
-	ld	r29,0(r29)
-	mtlr	r29              /* fn addr in lr */
-	mr	r3,r30	        /* load arg and call fn */
-	blrl
-	li	r0,__NR_exit	/* exit after child exits */
-        li	r3,0
-	sc
-2:	addi	r1,r1,STACK_FRAME_OVERHEAD
-	ld	r29,-24(r1)
-	ld	r30,-16(r1)
-	blr
-
 /*
  * disable_kernel_fp()
  * Disable the FPU.

arch/powerpc/kernel/ppc_ksyms.c

@@ -94,7 +94,6 @@ EXPORT_SYMBOL(pci_dram_offset);
 #endif /* CONFIG_PCI */
 
 EXPORT_SYMBOL(start_thread);
-EXPORT_SYMBOL(kernel_thread);
 
 EXPORT_SYMBOL(giveup_fpu);
 #ifdef CONFIG_ALTIVEC

arch/powerpc/kernel/process.c

@@ -734,30 +734,39 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 extern unsigned long dscr_default; /* defined in arch/powerpc/kernel/sysfs.c */
 
 int copy_thread(unsigned long clone_flags, unsigned long usp,
-		unsigned long unused, struct task_struct *p,
+		unsigned long arg, struct task_struct *p,
 		struct pt_regs *regs)
 {
 	struct pt_regs *childregs, *kregs;
 	extern void ret_from_fork(void);
+	extern void ret_from_kernel_thread(void);
+	void (*f)(void);
 	unsigned long sp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
 
-	CHECK_FULL_REGS(regs);
 	/* Copy registers */
 	sp -= sizeof(struct pt_regs);
 	childregs = (struct pt_regs *) sp;
-	*childregs = *regs;
-	if ((childregs->msr & MSR_PR) == 0) {
+	if (!regs) {
 		/* for kernel thread, set `current' and stackptr in new task */
+		memset(childregs, 0, sizeof(struct pt_regs));
 		childregs->gpr[1] = sp + sizeof(struct pt_regs);
-#ifdef CONFIG_PPC32
-		childregs->gpr[2] = (unsigned long) p;
-#else
+#ifdef CONFIG_PPC64
+		childregs->gpr[14] = *(unsigned long *)usp;
+		childregs->gpr[2] = ((unsigned long *)usp)[1],
 		clear_tsk_thread_flag(p, TIF_32BIT);
+#else
+		childregs->gpr[14] = usp;	/* function */
+		childregs->gpr[2] = (unsigned long) p;
 #endif
+		childregs->gpr[15] = arg;
 		p->thread.regs = NULL;	/* no user register state */
+		f = ret_from_kernel_thread;
 	} else {
+		CHECK_FULL_REGS(regs);
+		*childregs = *regs;
 		childregs->gpr[1] = usp;
 		p->thread.regs = childregs;
+		childregs->gpr[3] = 0;  /* Result from fork() */
 		if (clone_flags & CLONE_SETTLS) {
 #ifdef CONFIG_PPC64
 			if (!is_32bit_task())
@@ -766,8 +775,9 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 #endif
 				childregs->gpr[2] = childregs->gpr[6];
 		}
+
+		f = ret_from_fork;
 	}
-	childregs->gpr[3] = 0;  /* Result from fork() */
 	sp -= STACK_FRAME_OVERHEAD;
 
 	/*
@@ -806,7 +816,6 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 		p->thread.dscr = current->thread.dscr;
 	}
 #endif
-
 	/*
 	 * The PPC64 ABI makes use of a TOC to contain function 
 	 * pointers.  The function (ret_from_except) is actually a pointer
@@ -814,11 +823,10 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 	 * function.
 	 */
 #ifdef CONFIG_PPC64
-	kregs->nip = *((unsigned long *)ret_from_fork);
+	kregs->nip = *((unsigned long *)f);
 #else
-	kregs->nip = (unsigned long)ret_from_fork;
+	kregs->nip = (unsigned long)f;
 #endif
-
 	return 0;
 }