[linuxsh-dev] gUSA support

[NIIBE Y. <gn...@m1...>]

Here's experimental patch to support user space atomicity emulation
(this is for 2.4.18).

Please see this:
	http://sources.redhat.com/ml/libc-hacker/2002-05/msg00029.html

It explains how gUSA works.

I believe that this does _not_ impact performance.

Comments are welcome.

2002-05-22  NIIBE Yutaka  <gn...@m1...>

	gUSA ("g" User Space Atomicity) support.
	* arch/sh/kernel/signal.c (handle_signal): Added gUSA handling.
	* arch/sh/kernel/entry.S (reschedule): Added gUSA handling.

Index: arch/sh/kernel/entry.S
===================================================================
RCS file: /cvsroot/linuxsh/linux/arch/sh/kernel/entry.S,v
retrieving revision 1.1.1.1.2.4
diff -u -3 -p -r1.1.1.1.2.4 entry.S
--- arch/sh/kernel/entry.S	10 May 2002 17:58:54 -0000	1.1.1.1.2.4
+++ arch/sh/kernel/entry.S	22 May 2002 02:15:26 -0000
@@ -94,6 +94,7 @@ OFF_R5         =  20     	/* New ABI: ar
 OFF_R6         =  24     	/* New ABI: arg2 */
 OFF_R7         =  28     	/* New ABI: arg3 */
 OFF_SP	   =  (15*4)
+OFF_PC	   =  (16*4)
 OFF_SR	   =  (16*4+8)
 OFF_TRA    =  (16*4+6*4)
 
@@ -455,12 +456,24 @@ __INV_IMASK:
 
 	.align	2
 reschedule:
-	mova	SYMBOL_NAME(ret_from_syscall), r0
-	mov.l	1f, r1
-	jmp	@r1
+	! gUSA handling
+	mov.l	@(OFF_SP,r15), r1	! get user space stack pointer
+	cmp/pz	r1
+	bt/s	1f
+	 mov.l	2f, r4
+	mov	#OFF_PC, r0
+	mov.l	@(r0,r15), r2		! get user space PC (program counter)
+	mov.l	@(OFF_R0,r15), r3	! end point
+	cmp/hs	r3, r2			! r2 >= r3? 
+	bt	1f
+	add	r2, r1			! reentrance point #2
+	mov.l	r1, @(r0,r15)		! reset PC to reentrance point #2
+	!
+1:	mova	SYMBOL_NAME(ret_from_syscall), r0
+	jmp	@r4
 	 lds	r0, pr
 	.align	2
-1:	.long	SYMBOL_NAME(schedule)
+2:	.long	SYMBOL_NAME(schedule)
 
 ret_from_irq:
 ret_from_exception:
Index: arch/sh/kernel/signal.c
===================================================================
RCS file: /cvsroot/linuxsh/linux/arch/sh/kernel/signal.c,v
retrieving revision 1.1.1.1.2.1
diff -u -3 -p -r1.1.1.1.2.1 signal.c
--- arch/sh/kernel/signal.c	29 Mar 2002 00:01:07 -0000	1.1.1.1.2.1
+++ arch/sh/kernel/signal.c	22 May 2002 02:15:26 -0000
@@ -533,6 +533,17 @@ handle_signal(unsigned long sig, struct 
 			case -ERESTARTNOINTR:
 				regs->pc -= 2;
 		}
+	} else {
+		/* gUSA handling */
+		if (regs->regs[15] >= 0x80000000) {
+			int offset = (int)regs->regs[15];
+
+			/* Reset stack pointer: clear critical region mark */
+			regs->regs[15] = regs->regs[1];
+			if (regs->pc < regs->regs[0])
+				/* Go to reentrance point #1 */
+				regs->pc = regs->regs[0] + offset - 2;
+		}
 	}
 
 	/* Set up the stack frame */