alpha: simplify fork and friends

* no need to restore everything from switch_stack when we only need $26
* no need to pass current_pt_regs() manually, we can just as easily
calculate it in alpha_clone/alpha_vfork ($8 + constant)
* interpretation of zero usp as "use the parent's" is simpler in copy_thread();
let fork and vfork just pass 0.

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

2 files changed, 14 insertions, 19 deletions

diff --git a/arch/alpha/kernel/entry.S b/arch/alpha/kernel/entry.S
index a7607832dd4f..cc6d34e9e2ea 100644
--- a/arch/alpha/kernel/entry.S
+++ b/arch/alpha/kernel/entry.S
@@ -617,7 +617,6 @@ ret_from_kernel_thread:
         .ent    sys_fork
 sys_fork:
         .prologue 0
-        mov     $sp, $21
         bsr     $1, do_switch_stack
         bis     $31, SIGCHLD, $16
         mov     $31, $17
@@ -625,7 +624,9 @@ sys_fork:
         mov     $31, $19
         mov     $31, $20
         jsr     $26, alpha_clone
-        bsr     $1, undo_switch_stack
+fork_out:
+        ldq     $26, 56($sp)
+        lda     $sp, SWITCH_STACK_SIZE($sp)
         ret
 .end sys_fork
 
@@ -634,12 +635,10 @@ sys_fork:
         .ent    sys_clone
 sys_clone:
         .prologue 0
-        mov     $sp, $21
         bsr     $1, do_switch_stack
         /* $16, $17, $18, $19, $20 come from the user.  */
-        jsr     $26, alpha_clone
-        bsr     $1, undo_switch_stack
-        ret
+        lda     $26, fork_out
+        jsr     $31, alpha_clone
 .end sys_clone
 
         .align  4
@@ -647,11 +646,9 @@ sys_clone:
         .ent    sys_vfork
 sys_vfork:
         .prologue 0
-        mov     $sp, $16
         bsr     $1, do_switch_stack
-        jsr     $26, alpha_vfork
-        bsr     $1, undo_switch_stack
-        ret
+        lda     $26, fork_out
+        jsr     $31, alpha_vfork
 .end sys_vfork
 
         .align  4
diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
index 51987dcf79b8..ad86c099b6f5 100644
--- a/arch/alpha/kernel/process.c
+++ b/arch/alpha/kernel/process.c
@@ -246,19 +246,17 @@ release_thread(struct task_struct *dead_task)
 int
 alpha_clone(unsigned long clone_flags, unsigned long usp,
             int __user *parent_tid, int __user *child_tid,
-            unsigned long tls_value, struct pt_regs *regs)
+            unsigned long tls_value)
 {
-        if (!usp)
-                usp = rdusp();
-
-        return do_fork(clone_flags, usp, regs, 0, parent_tid, child_tid);
+        return do_fork(clone_flags, usp, current_pt_regs(), 0,
+                        parent_tid, child_tid);
 }
 
 int
-alpha_vfork(struct pt_regs *regs)
+alpha_vfork(void)
 {
-        return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, rdusp(),
-                       regs, 0, NULL, NULL);
+        return do_fork(CLONE_VFORK | CLONE_VM | SIGCHLD, 0,
+                       current_pt_regs(), 0, NULL, NULL);
 }
 
 /*
@@ -301,7 +299,7 @@ copy_thread(unsigned long clone_flags, unsigned long usp,
         stack = ((struct switch_stack *) regs) - 1;
         *childstack = *stack;
         childstack->r26 = (unsigned long) ret_from_fork;
-        childti->pcb.usp = usp;
+        childti->pcb.usp = usp ?: rdusp();
         childti->pcb.ksp = (unsigned long) childstack;
         childti->pcb.flags = 1; /* set FEN, clear everything else */