openrisc: use generic kernel_thread/kernel_execve

Signed-off-by: Jonas Bonn <jonas@southpole.se>

3 files changed, 68 insertions, 102 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/kernel/entry.S b/arch/openrisc/kernel/entry.S
index 374e63e7c9f6..dce86aef8aba 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 ] === */
 
 /*
diff --git a/arch/openrisc/kernel/process.c b/arch/openrisc/kernel/process.c
index ad26d5af2649..a0f467e438fc 100644
--- a/arch/openrisc/kernel/process.c
+++ b/arch/openrisc/kernel/process.c
@@ -109,65 +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 {
-                childregs->sp = usp;
-        }
-
-        childregs->gpr[11] = 0; /* Result from fork() */
+                *userregs = *regs;
 
-        /*
-         * The way this works is that at some point in the future
-         * some task will call _switch to switch to the new task.
-         * That will pop off the stack frame created below and start
-         * the new task running at ret_from_fork.  The new task will
-         * do some house keeping and then return from the fork or clone
-         * system call, using the stack frame created above.
-         */
-        /* redzone */
-        sp -= STACK_FRAME_OVERHEAD;
-        sp -= sizeof(struct pt_regs);
-        kregs = (struct pt_regs *)sp;
+                userregs->sp = usp;
+                userregs->gpr[11] = 0;  /* Result from fork() */
 
-        ti = task_thread_info(p);
-        ti->ksp = sp;
+                kregs->gpr[20] = 0;     /* Userspace thread */
+        }
 
-        /* kregs->sp must store the location of the 'pre-switch' kernel stack
-         * pointer... for a newly forked process, this is simply the top of
-         * the kernel stack.
+        /*
+         * _switch wants the kernel stack page in pt_regs->sp so that it
+         * can restore it to thread_info->ksp... see _switch for details.
          */
         kregs->sp = top_of_kernel_stack;
-        kregs->gpr[10] = (unsigned long)task_thread_info(p);
         kregs->gpr[9] = (unsigned long)ret_from_fork;
 
+        task_thread_info(p)->ksp = (unsigned long)kregs;
+
         return 0;
 }
 
@@ -176,16 +193,14 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
  */
 void start_thread(struct pt_regs *regs, unsigned long pc, unsigned long sp)
 {
-        unsigned long sr = regs->sr & ~SPR_SR_SM;
+        unsigned long sr = mfspr(SPR_SR) & ~SPR_SR_SM;
 
         set_fs(USER_DS);
-        memset(regs->gpr, 0, sizeof(regs->gpr));
+        memset(regs, 0, sizeof(struct pt_regs));
 
         regs->pc = pc;
         regs->sr = sr;
         regs->sp = sp;
-
-/*      printk("start thread, ksp = %lx\n", current_thread_info()->ksp);*/
 }
 
 /* Fill in the fpu structure for a core dump.  */
@@ -236,31 +251,6 @@ void dump_elf_thread(elf_greg_t *dest, struct pt_regs* regs)
         dest[35] = 0;
 }
 
-extern void _kernel_thread_helper(void);
-
-void __noreturn kernel_thread_helper(int (*fn) (void *), void *arg)
-{
-        do_exit(fn(arg));
-}
-
-/*
- * 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.gpr[20] = (unsigned long)fn;
-        regs.gpr[22] = (unsigned long)arg;
-        regs.sr = mfspr(SPR_SR);
-        regs.pc = (unsigned long)_kernel_thread_helper;
-
-        return do_fork(flags | CLONE_VM | CLONE_UNTRACED,
-                       0, &regs, 0, NULL, NULL);
-}
-
 /*
  * sys_execve() executes a new program.
  */
@@ -291,19 +281,3 @@ unsigned long get_wchan(struct task_struct *p)
 
         return 0;
 }
-
-int kernel_execve(const char *filename, char *const argv[], char *const envp[])
-{
-        register long __res asm("r11") = __NR_execve;
-        register long __a asm("r3") = (long)(filename);
-        register long __b asm("r4") = (long)(argv);
-        register long __c asm("r5") = (long)(envp);
-        __asm__ volatile ("l.sys 1"
-                          : "=r" (__res), "=r"(__a), "=r"(__b), "=r"(__c)
-                          : "0"(__res), "1"(__a), "2"(__b), "3"(__c)
-                          : "r6", "r7", "r8", "r12", "r13", "r15",
-                            "r17", "r19", "r21", "r23", "r25", "r27",
-                            "r29", "r31");
-        __asm__ volatile ("l.nop");
-        return __res;
-}