linux-kernel - [RFC PATCH v1 28/31] ARC: split ret_from_fork, simplify kernel

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Date:	Wed,  7 Nov 2012 10:47:51 +0100
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	tglx@...utronix.de, arnd@...db.de,
	Vineet Gupta <Vineet.Gupta1@...opsys.com>
Subject: [RFC PATCH v1 28/31] ARC: split ret_from_fork, simplify kernel_thread()

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
---
 arch/arc/kernel/entry.S   |    8 ++++++++
 arch/arc/kernel/process.c |   32 +++++++++++++-------------------
 2 files changed, 21 insertions(+), 19 deletions(-)

diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index fe9a17c..46d0280 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -580,6 +580,14 @@ ARC_ENTRY ret_from_fork
 	b @ret_from_exception
 ARC_EXIT ret_from_fork
 
+ARC_ENTRY ret_from_kernel_thread
+	bl  @schedule_tail
+	ld  r1, [sp, PT_r1]
+	j.d [r1]
+	ld  r0, [sp, PT_r0]
+	j   @sys_exit
+ARC_EXIT ret_from_kernel_thread
+
 ;################### Special Sys Call Wrappers ##########################
 
 ARC_ENTRY sys_execve_wrapper
diff --git a/arch/arc/kernel/process.c b/arch/arc/kernel/process.c
index c116fa5..fee3e11 100644
--- a/arch/arc/kernel/process.c
+++ b/arch/arc/kernel/process.c
@@ -142,24 +142,13 @@ void cpu_idle(void)
 	}
 }
 
-void kernel_thread_helper(void)
-{
-	__asm__ __volatile__(
-		"mov   r0, r2	\n\t"
-		"mov   r1, r3	\n\t"
-		"j     [r1]	\n\t");
-}
-
 int kernel_thread(int (*fn) (void *), void *arg, unsigned long flags)
 {
-	struct pt_regs regs;
+	struct pt_regs regs = {
+		.r0 = (unsigned long)arg,
+		.r1 = (unsigned long)fn
+	};
 
-	memset(&regs, 0, sizeof(regs));
-
-	regs.r2 = (unsigned long)arg;
-	regs.r3 = (unsigned long)fn;
-	regs.blink = (unsigned long)do_exit;
-	regs.ret = (unsigned long)kernel_thread_helper;
 	regs.status32 = read_aux_reg(0xa);
 
 	/* Ok, create the new process.. */
@@ -170,6 +159,7 @@ int kernel_thread(int (*fn) (void *), void *arg, unsigned long flags)
 EXPORT_SYMBOL(kernel_thread);
 
 asmlinkage void ret_from_fork(void);
+asmlinkage void ret_from_kernel_thread(void) __attribute__((noreturn));
 
 /* Layout of Child kernel mode stack as setup at the end of this function is
  *
@@ -226,18 +216,22 @@ int copy_thread(unsigned long clone_flags,
 	/* Copy parents pt regs on child's kernel mode stack */
 	*c_regs = *regs;
 
-	/* __switch_to expects FP(0), BLINK(return addr) at top of stack */
-	childksp[0] = 0;				/* for POP fp */
-	childksp[1] = (unsigned long)ret_from_fork;	/* for POP blink */
-
 	if (!(user_mode(regs))) {
 		c_regs->sp =
 		    (unsigned long)task_thread_info(p) + (THREAD_SIZE - 4);
+
+		/* __switch_to expects FP(0), BLINK(return addr) at top */
+		childksp[0] = 0;			/* fp */
+		childksp[1] = (unsigned long)ret_from_kernel_thread; /* blink */
 		return 0;
 	}
 
 	/*--------- User Task Only --------------*/
 
+	/* __switch_to expects FP(0), BLINK(return addr) at top of stack */
+	childksp[0] = 0;				/* for POP fp */
+	childksp[1] = (unsigned long)ret_from_fork;	/* for POP blink */
+
 	c_regs->sp = usp;
 	c_regs->r0 = 0;		/* fork returns 0 in child */
 
-- 
1.7.4.1

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