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>

arch/parisc/kernel/entry.S

@@ -719,7 +719,7 @@ ENTRY(ret_from_kernel_thread)
 	BL	schedule_tail, %r2
 	nop
 
-	LDREG	TI_TASK-THREAD_SZ_ALGN(%r30), %r1
+	LDREG	TI_TASK-THREAD_SZ_ALGN-FRAME_SIZE(%r30), %r1
 	LDREG	TASK_PT_GR25(%r1), %r26
 #ifdef CONFIG_64BIT
 	LDREG	TASK_PT_GR27(%r1), %r27
@@ -743,9 +743,8 @@ ENDPROC(ret_from_kernel_thread)
 
 ENTRY(ret_from_kernel_execve)
 	mfctl   %cr30, %r1
-	ldo	THREAD_SZ_ALGN(%r1), %r30
-	b	intr_return	/* forward */
-	copy	%r26,%r16	/* pt_regs into r16 */
+	b	syscall_exit	/* forward */
+	ldo	THREAD_SZ_ALGN+FRAME_SIZE(%r1), %r30
 ENDPROC(ret_from_kernel_execve)
 
 
@@ -1709,39 +1708,13 @@ ENTRY(sys_fork_wrapper)
 	LDREG	TI_TASK-THREAD_SZ_ALGN-FRAME_SIZE(%r30), %r1
 	ldo	TASK_REGS(%r1),%r1
 	reg_save %r1
-	mfctl	%cr27, %r3
-	STREG	%r3, PT_CR27(%r1)
-
-	STREG	%r2,-RP_OFFSET(%r30)
-	ldo	FRAME_SIZE(%r30),%r30
-#ifdef CONFIG_64BIT
-	ldo	-16(%r30),%r29		/* Reference param save area */
-#endif
-
-	/* These are call-clobbered registers and therefore
-	   also syscall-clobbered (we hope). */
-	STREG	%r2,PT_GR19(%r1)	/* save for child */
-	STREG	%r30,PT_GR21(%r1)
+	mfctl	%cr27, %r28
+	STREG	%r28, PT_CR27(%r1)
 
 	LDREG	PT_GR30(%r1),%r25
 	copy	%r1,%r24
-	BL	sys_clone,%r2
+	b	sys_clone
 	ldi	SIGCHLD,%r26
-
-	LDREG	-RP_OFFSET-FRAME_SIZE(%r30),%r2
-wrapper_exit:
-	ldo	-FRAME_SIZE(%r30),%r30		/* get the stackframe */
-	LDREG	TI_TASK-THREAD_SZ_ALGN-FRAME_SIZE(%r30),%r1
-	ldo	TASK_REGS(%r1),%r1	 /* get pt regs */
-
-	LDREG	PT_CR27(%r1), %r3
-	mtctl	%r3, %cr27
-	reg_restore %r1
-
-	/* strace expects syscall # to be preserved in r20 */
-	ldi	__NR_fork,%r20
-	bv %r0(%r2)
-	STREG	%r20,PT_GR20(%r1)
 ENDPROC(sys_fork_wrapper)
 
 	/* Set the return value for the child */
@@ -1749,9 +1722,13 @@ ENTRY(child_return)
 	BL	schedule_tail, %r2
 	nop
 
-	LDREG	TI_TASK-THREAD_SZ_ALGN-FRAME_SIZE-FRAME_SIZE(%r30), %r1
-	LDREG	TASK_PT_GR19(%r1),%r2
-	b	wrapper_exit
+	LDREG	TI_TASK-THREAD_SZ_ALGN-FRAME_SIZE(%r30), %r1
+	ldo	TASK_REGS(%r1),%r1	 /* get pt regs */
+
+	LDREG	PT_CR27(%r1), %r3
+	mtctl	%r3, %cr27
+	reg_restore %r1
+	b	syscall_exit
 	copy	%r0,%r28
 ENDPROC(child_return)
 
@@ -1760,23 +1737,10 @@ ENTRY(sys_clone_wrapper)
 	LDREG	TI_TASK-THREAD_SZ_ALGN-FRAME_SIZE(%r30),%r1
 	ldo	TASK_REGS(%r1),%r1	/* get pt regs */
 	reg_save %r1
-	mfctl	%cr27, %r3
-	STREG	%r3, PT_CR27(%r1)
-
-	STREG	%r2,-RP_OFFSET(%r30)
-	ldo	FRAME_SIZE(%r30),%r30
-#ifdef CONFIG_64BIT
-	ldo	-16(%r30),%r29		/* Reference param save area */
-#endif
-
-	/* WARNING - Clobbers r19 and r21, userspace must save these! */
-	STREG	%r2,PT_GR19(%r1)	/* save for child */
-	STREG	%r30,PT_GR21(%r1)
-	BL	sys_clone,%r2
+	mfctl	%cr27, %r28
+	STREG	%r28, PT_CR27(%r1)
+	b	sys_clone
 	copy	%r1,%r24
-
-	b	wrapper_exit
-	LDREG	-RP_OFFSET-FRAME_SIZE(%r30),%r2
 ENDPROC(sys_clone_wrapper)
 
 
@@ -1784,23 +1748,11 @@ ENTRY(sys_vfork_wrapper)
 	LDREG	TI_TASK-THREAD_SZ_ALGN-FRAME_SIZE(%r30),%r1
 	ldo	TASK_REGS(%r1),%r1	/* get pt regs */
 	reg_save %r1
-	mfctl	%cr27, %r3
-	STREG	%r3, PT_CR27(%r1)
-
-	STREG	%r2,-RP_OFFSET(%r30)
-	ldo	FRAME_SIZE(%r30),%r30
-#ifdef CONFIG_64BIT
-	ldo	-16(%r30),%r29		/* Reference param save area */
-#endif
+	mfctl	%cr27, %r28
+	STREG	%r28, PT_CR27(%r1)
 
-	STREG	%r2,PT_GR19(%r1)	/* save for child */
-	STREG	%r30,PT_GR21(%r1)
-
-	BL	sys_vfork,%r2
+	b	sys_vfork
 	copy	%r1,%r26
-
-	b	wrapper_exit
-	LDREG	-RP_OFFSET-FRAME_SIZE(%r30),%r2
 ENDPROC(sys_vfork_wrapper)
 
 	

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;