arm: switch to saner kernel_execve() semantics

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

arch/arm/Kconfig

@@ -50,6 +50,7 @@ config ARM
 	select GENERIC_STRNLEN_USER
 	select DCACHE_WORD_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && !CPU_BIG_ENDIAN
 	select GENERIC_KERNEL_THREAD
+	select GENERIC_KERNEL_EXECVE
 	help
 	  The ARM series is a line of low-power-consumption RISC chip designs
 	  licensed by ARM Ltd and targeted at embedded applications and

arch/arm/include/asm/unistd.h

@@ -470,7 +470,6 @@
 #define __ARCH_WANT_SYS_SOCKETCALL
 #endif
 #define __ARCH_WANT_SYS_EXECVE
-#define __ARCH_WANT_KERNEL_EXECVE
 
 /*
  * "Conditional" syscalls

arch/arm/kernel/entry-common.S

@@ -86,35 +86,14 @@ ENDPROC(ret_to_user)
  */
 ENTRY(ret_from_fork)
 	bl	schedule_tail
+	cmp	r5, #0
+	movne	r0, r4
+	movne	lr, pc
+	movne	pc, r5
 	get_thread_info tsk
-	mov	why, #1
 	b	ret_slow_syscall
 ENDPROC(ret_from_fork)
 
-ENTRY(ret_from_kernel_thread)
- UNWIND(.fnstart)
- UNWIND(.cantunwind)
-	bl	schedule_tail
-	mov	r0, r4
-	adr	lr, BSYM(1f)	@ kernel threads should not exit
-	mov	pc, r5
-1:	bl	do_exit
-	nop
- UNWIND(.fnend)
-ENDPROC(ret_from_kernel_thread)
-
-/*
- * turn a kernel thread into userland process
- * use: ret_from_kernel_execve(struct pt_regs *normal)
- */
-ENTRY(ret_from_kernel_execve)
-	mov	why, #0			@ not a syscall
-	str	why, [r0, #S_R0]	@ ... and we want 0 in ->ARM_r0 as well
-	get_thread_info tsk		@ thread structure
-	mov	sp, r0			@ stack pointer just under pt_regs
-	b	ret_slow_syscall
-ENDPROC(ret_from_kernel_execve)
-
 	.equ NR_syscalls,0
 #define CALL(x) .equ NR_syscalls,NR_syscalls+1
 #include "calls.S"

arch/arm/kernel/process.c

@@ -373,7 +373,6 @@ void release_thread(struct task_struct *dead_task)
 }
 
 asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
-asmlinkage void ret_from_kernel_thread(void) __asm__("ret_from_kernel_thread");
 
 int
 copy_thread(unsigned long clone_flags, unsigned long stack_start,
@@ -388,13 +387,13 @@ copy_thread(unsigned long clone_flags, unsigned long stack_start,
 		*childregs = *regs;
 		childregs->ARM_r0 = 0;
 		childregs->ARM_sp = stack_start;
-		thread->cpu_context.pc = (unsigned long)ret_from_fork;
 	} else {
+		memset(childregs, 0, sizeof(struct pt_regs));
 		thread->cpu_context.r4 = stk_sz;
 		thread->cpu_context.r5 = stack_start;
-		thread->cpu_context.pc = (unsigned long)ret_from_kernel_thread;
 		childregs->ARM_cpsr = SVC_MODE;
 	}
+	thread->cpu_context.pc = (unsigned long)ret_from_fork;
 	thread->cpu_context.sp = (unsigned long)childregs;
 
 	clear_ptrace_hw_breakpoint(p);