arm: split ret_from_fork, simplify kernel_thread() [based on patch by rmk]

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

2 files changed, 25 insertions, 62 deletions

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 978eac57e04..9a48b7a577e 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -91,6 +91,18 @@ ENTRY(ret_from_fork)
         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)
+
         .equ NR_syscalls,0
 #define CALL(x) .equ NR_syscalls,NR_syscalls+1
 #include "calls.S"
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 693b744fd57..c10e4395bc4 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -373,6 +373,7 @@ 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,
@@ -381,13 +382,20 @@ copy_thread(unsigned long clone_flags, unsigned long stack_start,
         struct thread_info *thread = task_thread_info(p);
         struct pt_regs *childregs = task_pt_regs(p);
 
-        *childregs = *regs;
-        childregs->ARM_r0 = 0;
-        childregs->ARM_sp = stack_start;
-
         memset(&thread->cpu_context, 0, sizeof(struct cpu_context_save));
+
+        if (likely(regs)) {
+                *childregs = *regs;
+                childregs->ARM_r0 = 0;
+                childregs->ARM_sp = stack_start;
+                thread->cpu_context.pc = (unsigned long)ret_from_fork;
+        } else {
+                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.sp = (unsigned long)childregs;
-        thread->cpu_context.pc = (unsigned long)ret_from_fork;
 
         clear_ptrace_hw_breakpoint(p);
 
@@ -423,63 +431,6 @@ int dump_fpu (struct pt_regs *regs, struct user_fp *fp)
 }
 EXPORT_SYMBOL(dump_fpu);
 
-/*
- * Shuffle the argument into the correct register before calling the
- * thread function.  r4 is the thread argument, r5 is the pointer to
- * the thread function, and r6 points to the exit function.
- */
-extern void kernel_thread_helper(void);
-asm(    ".pushsection .text\n"
-"       .align\n"
-"       .type   kernel_thread_helper, #function\n"
-"kernel_thread_helper:\n"
-#ifdef CONFIG_TRACE_IRQFLAGS
-"       bl      trace_hardirqs_on\n"
-#endif
-"       msr     cpsr_c, r7\n"
-"       mov     r0, r4\n"
-"       mov     lr, r6\n"
-"       mov     pc, r5\n"
-"       .size   kernel_thread_helper, . - kernel_thread_helper\n"
-"       .popsection");
-
-#ifdef CONFIG_ARM_UNWIND
-extern void kernel_thread_exit(long code);
-asm(    ".pushsection .text\n"
-"       .align\n"
-"       .type   kernel_thread_exit, #function\n"
-"kernel_thread_exit:\n"
-"       .fnstart\n"
-"       .cantunwind\n"
-"       bl      do_exit\n"
-"       nop\n"
-"       .fnend\n"
-"       .size   kernel_thread_exit, . - kernel_thread_exit\n"
-"       .popsection");
-#else
-#define kernel_thread_exit      do_exit
-#endif
-
-/*
- * Create a kernel thread.
- */
-pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
-{
-        struct pt_regs regs;
-
-        memset(&regs, 0, sizeof(regs));
-
-        regs.ARM_r4 = (unsigned long)arg;
-        regs.ARM_r5 = (unsigned long)fn;
-        regs.ARM_r6 = (unsigned long)kernel_thread_exit;
-        regs.ARM_r7 = SVC_MODE | PSR_ENDSTATE | PSR_ISETSTATE;
-        regs.ARM_pc = (unsigned long)kernel_thread_helper;
-        regs.ARM_cpsr = regs.ARM_r7 | PSR_I_BIT;
-
-        return do_fork(flags|CLONE_VM|CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
-}
-EXPORT_SYMBOL(kernel_thread);
-
 unsigned long get_wchan(struct task_struct *p)
 {
         struct stackframe frame;