4 files changed, 77 insertions, 133 deletions

diff --git a/arch/openrisc/Kconfig b/arch/openrisc/Kconfig
index 05f2ba41ff1a..e7f1a2993f78 100644
--- a/arch/openrisc/Kconfig
+++ b/arch/openrisc/Kconfig
@@ -22,6 +22,8 @@ config OPENRISC
         select GENERIC_STRNCPY_FROM_USER
         select GENERIC_STRNLEN_USER
         select MODULES_USE_ELF_RELA
+        select GENERIC_KERNEL_THREAD
+        select GENERIC_KERNEL_EXECVE
 
 config MMU
         def_bool y
diff --git a/arch/openrisc/include/uapi/asm/unistd.h b/arch/openrisc/include/uapi/asm/unistd.h
index 437bdbb61b14..5db7bc0fa5a7 100644
--- a/arch/openrisc/include/uapi/asm/unistd.h
+++ b/arch/openrisc/include/uapi/asm/unistd.h
@@ -20,6 +20,8 @@
 
 #define sys_mmap2 sys_mmap_pgoff
 
+#define __ARCH_WANT_SYS_EXECVE
+
 #include <asm-generic/unistd.h>
 
 #define __NR_or1k_atomic __NR_arch_specific_syscall
diff --git a/arch/openrisc/kernel/entry.S b/arch/openrisc/kernel/entry.S
index ddfcaa828b0e..c60a09df323f 100644
--- a/arch/openrisc/kernel/entry.S
+++ b/arch/openrisc/kernel/entry.S
@@ -894,6 +894,16 @@ ENTRY(ret_from_fork)
         l.jal   schedule_tail
          l.nop
 
+        /* Check if we are a kernel thread */
+        l.sfeqi r20,0
+        l.bf    1f
+         l.nop
+
+        /* ...we are a kernel thread so invoke the requested callback */
+        l.jalr  r20
+         l.or   r3,r22,r0
+
+1:
         /* _syscall_returns expect r11 to contain return value */
         l.lwz   r11,PT_GPR11(r1)
 
@@ -915,26 +925,6 @@ ENTRY(ret_from_fork)
         l.j     _syscall_return
          l.nop
 
-/* Since syscalls don't save call-clobbered registers, the args to
- * kernel_thread_helper will need to be passed through callee-saved
- * registers and copied to the parameter registers when the thread
- * begins running.
- *
- * See arch/openrisc/kernel/process.c:
- * The args are passed as follows:
- *   arg1 (r3) : passed in r20
- *   arg2 (r4) : passed in r22
- */
-
-ENTRY(_kernel_thread_helper)
-        l.or    r3,r20,r0
-        l.or    r4,r22,r0
-        l.movhi r31,hi(kernel_thread_helper)
-        l.ori   r31,r31,lo(kernel_thread_helper)
-        l.jr    r31
-         l.nop
-
-
 /* ========================================================[ switch ] === */
 
 /*
@@ -1044,8 +1034,13 @@ ENTRY(_switch)
         /* Unwind stack to pre-switch state */
         l.addi  r1,r1,(INT_FRAME_SIZE)
 
-        /* Return via the link-register back to where we 'came from', where that can be
-         * either schedule() or return_from_fork()... */
+        /* Return via the link-register back to where we 'came from', where
+         * that may be either schedule(), ret_from_fork(), or
+         * ret_from_kernel_thread().  If we are returning to a new thread,
+         * we are expected to have set up the arg to schedule_tail already,
+         * hence we do so here unconditionally:
+         */
+        l.lwz   r3,TI_STACK(r3)         /* Load 'prev' as schedule_tail arg */
         l.jr    r9
          l.nop
 
@@ -1088,10 +1083,6 @@ ENTRY(sys_fork)
         l.j     _fork_save_extra_regs_and_call
          l.addi r3,r1,0
 
-ENTRY(sys_execve)
-        l.j     _sys_execve
-         l.addi r6,r1,0
-
 ENTRY(sys_sigaltstack)
         l.j     _sys_sigaltstack
          l.addi r5,r1,0
diff --git a/arch/openrisc/kernel/process.c b/arch/openrisc/kernel/process.c
index c35f3ab1a8d3..e0874b8e09e4 100644
--- a/arch/openrisc/kernel/process.c
+++ b/arch/openrisc/kernel/process.c
@@ -109,66 +109,82 @@ void release_thread(struct task_struct *dead_task)
  */
 extern asmlinkage void ret_from_fork(void);
 
+/*
+ * copy_thread
+ * @clone_flags: flags
+ * @usp: user stack pointer or fn for kernel thread
+ * @arg: arg to fn for kernel thread; always NULL for userspace thread
+ * @p: the newly created task
+ * @regs: CPU context to copy for userspace thread; always NULL for kthread
+ *
+ * At the top of a newly initialized kernel stack are two stacked pt_reg
+ * structures.  The first (topmost) is the userspace context of the thread.
+ * The second is the kernelspace context of the thread.
+ *
+ * A kernel thread will not be returning to userspace, so the topmost pt_regs
+ * struct can be uninitialized; it _does_ need to exist, though, because
+ * a kernel thread can become a userspace thread by doing a kernel_execve, in
+ * which case the topmost context will be initialized and used for 'returning'
+ * to userspace.
+ *
+ * The second pt_reg struct needs to be initialized to 'return' to
+ * ret_from_fork.  A kernel thread will need to set r20 to the address of
+ * a function to call into (with arg in r22); userspace threads need to set
+ * r20 to NULL in which case ret_from_fork will just continue a return to
+ * userspace.
+ *
+ * A kernel thread 'fn' may return; this is effectively what happens when
+ * kernel_execve is called.  In that case, the userspace pt_regs must have
+ * been initialized (which kernel_execve takes care of, see start_thread
+ * below); ret_from_fork will then continue its execution causing the
+ * 'kernel thread' to return to userspace as a userspace thread.
+ */
+
 int
 copy_thread(unsigned long clone_flags, unsigned long usp,
-            unsigned long unused, struct task_struct *p, struct pt_regs *regs)
+            unsigned long arg, struct task_struct *p, struct pt_regs *regs)
 {
-        struct pt_regs *childregs;
+        struct pt_regs *userregs;
         struct pt_regs *kregs;
         unsigned long sp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
-        struct thread_info *ti;
         unsigned long top_of_kernel_stack;
 
         top_of_kernel_stack = sp;
 
         p->set_child_tid = p->clear_child_tid = NULL;
 
-        /* Copy registers */
-        /* redzone */
-        sp -= STACK_FRAME_OVERHEAD;
+        /* Locate userspace context on stack... */
+        sp -= STACK_FRAME_OVERHEAD;     /* redzone */
         sp -= sizeof(struct pt_regs);
-        childregs = (struct pt_regs *)sp;
+        userregs = (struct pt_regs *) sp;
 
-        /* Copy parent registers */
-        *childregs = *regs;
+        /* ...and kernel context */
+        sp -= STACK_FRAME_OVERHEAD;     /* redzone */
+        sp -= sizeof(struct pt_regs);
+        kregs = (struct pt_regs *)sp;
 
-        if ((childregs->sr & SPR_SR_SM) == 1) {
-                /* for kernel thread, set `current_thread_info'
-                 * and stackptr in new task
-                 */
-                childregs->sp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
-                childregs->gpr[10] = (unsigned long)task_thread_info(p);
+        if (unlikely(p->flags & PF_KTHREAD)) {
+                memset(kregs, 0, sizeof(struct pt_regs));
+                kregs->gpr[20] = usp; /* fn, kernel thread */
+                kregs->gpr[22] = arg;
         } else {