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>

1 files changed, 7 insertions, 10 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