parisc: optimizations in copy_thread() and friends

* in user thread case the registers had been copied as part of task_struct
already; no need to do it in copy_thread().
* no need to store kernel stack pointer into regs->r21; we know its offset
anyway.
* no need to clobber r3 in sys_fork_wrapper and friends - r28 will do just
as well and *it* will be overwritten anyway.
* no need to mess with storing the return address for child - it should just
use syscall_exit.
* no need to bother with separate stack frame for sys_clone() - just branch
there and be done with that.
* no need to bother with wrapper_exit - we need it only on the child_return,
so let's just do it there.
* use the same ksp for kernel threads and userland ones, while we are at it,
and let ret_from_kernel_execve() go through the normal syscall_exit.  More
straightforward is better here...

[fixes from jejb folded]

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

1 files changed, 8 insertions, 20 deletions

diff --git a/arch/parisc/kernel/process.c b/arch/parisc/kernel/process.c
index 44e8534c52e..38db36f6430 100644
--- a/arch/parisc/kernel/process.c
+++ b/arch/parisc/kernel/process.c
@@ -52,6 +52,7 @@
 
 #include <asm/io.h>
 #include <asm/asm-offsets.h>
+#include <asm/assembly.h>
 #include <asm/pdc.h>
 #include <asm/pdc_chassis.h>
 #include <asm/pgalloc.h>
@@ -253,14 +254,16 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
 #ifdef CONFIG_HPUX
         extern void * const hpux_child_return;
 #endif
-
-        if (unlikely((p->flags & PF_KTHREAD) && usp != 0)) {
+        if (unlikely(p->flags & PF_KTHREAD)) {
                 memset(cregs, 0, sizeof(struct pt_regs));
+                if (!usp) /* idle thread */
+                        return 0;
+
                 /* kernel thread */
-                cregs->ksp = (unsigned long)stack + THREAD_SZ_ALGN;
                 /* Must exit via ret_from_kernel_thread in order
                  * to call schedule_tail()
                  */
+                cregs->ksp = (unsigned long)stack + THREAD_SZ_ALGN + FRAME_SIZE;
                 cregs->kpc = (unsigned long) &ret_from_kernel_thread;
                 /*
                  * Copy function and argument to be called from
@@ -275,22 +278,8 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
                 cregs->gr[25] = arg;
         } else {
                 /* user thread */
-                /*
-                 * Note that the fork wrappers are responsible
-                 * for setting gr[21].
-                 */
-
-                *cregs = *pregs;
-
-                /* Set the return value for the child.  Note that this is not
-                   actually restored by the syscall exit path, but we put it
-                   here for consistency in case of signals. */
-                cregs->gr[28] = 0; /* child */
-
-                /* Use same stack depth as parent */
-                cregs->ksp = (unsigned long)stack
-                        + (pregs->gr[21] & (THREAD_SIZE - 1));
                 cregs->gr[30] = usp;
+                cregs->ksp = (unsigned long)stack + THREAD_SZ_ALGN + FRAME_SIZE;
                 if (personality(p->personality) == PER_HPUX) {
 #ifdef CONFIG_HPUX
                         cregs->kpc = (unsigned long) &hpux_child_return;
@@ -302,8 +291,7 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
                 }
                 /* Setup thread TLS area from the 4th parameter in clone */
                 if (clone_flags & CLONE_SETTLS)
-                  cregs->cr27 = pregs->gr[23];
-        
+                        cregs->cr27 = pregs->gr[23];
         }
 
         return 0;