x86, 64-bit: Move kernel_thread to C

Prepare for merging with 32-bit.

Signed-off-by: Brian Gerst <brgerst@gmail.com>
LKML-Reference: <1260380084-3707-2-git-send-email-brgerst@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

3 files changed, 32 insertions, 50 deletions

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 63bca794c8f9..73d9b2c0e217 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -1166,63 +1166,20 @@ bad_gs:
         jmp  2b
         .previous
 
-/*
- * Create a kernel thread.
- *
- * C extern interface:
- *      extern long kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
- *
- * asm input arguments:
- *      rdi: fn, rsi: arg, rdx: flags
- */
-ENTRY(kernel_thread)
-        CFI_STARTPROC
-        FAKE_STACK_FRAME $child_rip
-        SAVE_ALL
-
-        # rdi: flags, rsi: usp, rdx: will be &pt_regs
-        movq %rdx,%rdi
-        orq  kernel_thread_flags(%rip),%rdi
-        movq $-1, %rsi
-        movq %rsp, %rdx
-
-        xorl %r8d,%r8d
-        xorl %r9d,%r9d
-
-        # clone now
-        call do_fork
-        movq %rax,RAX(%rsp)
-        xorl %edi,%edi
-
-        /*
-         * It isn't worth to check for reschedule here,
-         * so internally to the x86_64 port you can rely on kernel_thread()
-         * not to reschedule the child before returning, this avoids the need
-         * of hacks for example to fork off the per-CPU idle tasks.
-         * [Hopefully no generic code relies on the reschedule -AK]
-         */
-        RESTORE_ALL
-        UNFAKE_STACK_FRAME
-        ret
-        CFI_ENDPROC
-END(kernel_thread)
-
-ENTRY(child_rip)
+ENTRY(kernel_thread_helper)
         pushq $0                # fake return address
         CFI_STARTPROC
         /*
          * Here we are in the child and the registers are set as they were
          * at kernel_thread() invocation in the parent.
          */
-        movq %rdi, %rax
-        movq %rsi, %rdi
-        call *%rax
+        call *%rsi
         # exit
         mov %eax, %edi
         call do_exit
         ud2                     # padding for call trace
         CFI_ENDPROC
-END(child_rip)
+END(kernel_thread_helper)
 
 /*
  * execve(). This function needs to use IRET, not SYSRET, to set up all state properly.
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 83019f94b83d..92484c2130c6 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -59,8 +59,6 @@ asmlinkage extern void ret_from_fork(void);
 DEFINE_PER_CPU(unsigned long, old_rsp);
 static DEFINE_PER_CPU(unsigned char, is_idle);
 
-unsigned long kernel_thread_flags = CLONE_VM | CLONE_UNTRACED;
-
 static ATOMIC_NOTIFIER_HEAD(idle_notifier);
 
 void idle_notifier_register(struct notifier_block *n)
@@ -231,6 +229,35 @@ void show_regs(struct pt_regs *regs)
         show_trace(NULL, regs, (void *)(regs + 1), regs->bp);
 }
 
+/*
+ * This gets run with %si containing the
+ * function to call, and %di containing
+ * the "args".
+ */
+extern void kernel_thread_helper(void);
+
+/*
+ * Create a kernel thread
+ */
+int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
+{
+        struct pt_regs regs;
+
+        memset(&regs, 0, sizeof(regs));
+
+        regs.si = (unsigned long) fn;
+        regs.di = (unsigned long) arg;
+
+        regs.orig_ax = -1;
+        regs.ip = (unsigned long) kernel_thread_helper;
+        regs.cs = __KERNEL_CS;
+        regs.flags = X86_EFLAGS_IF;
+
+        /* Ok, create the new process.. */
+        return do_fork(flags | CLONE_VM | CLONE_UNTRACED, ~0UL, &regs, 0, NULL, NULL);
+}
+EXPORT_SYMBOL(kernel_thread);
+
 void release_thread(struct task_struct *dead_task)
 {
         if (dead_task->mm) {
diff --git a/arch/x86/kernel/x8664_ksyms_64.c b/arch/x86/kernel/x8664_ksyms_64.c
index a1029769b6f2..9fafaf83b3b8 100644
--- a/arch/x86/kernel/x8664_ksyms_64.c
+++ b/arch/x86/kernel/x8664_ksyms_64.c
@@ -17,8 +17,6 @@
 EXPORT_SYMBOL(mcount);
 #endif
 
-EXPORT_SYMBOL(kernel_thread);
-
 EXPORT_SYMBOL(__get_user_1);
 EXPORT_SYMBOL(__get_user_2);
 EXPORT_SYMBOL(__get_user_4);