powerpc: handle syscall error in clone.

sigsetjmp: store temporaries in jmp_buf rather than on stack.

src/signal/powerpc/sigsetjmp.s

@@ -10,25 +10,26 @@ sigsetjmp:
 	#2) if its 0, goto setjmp code
 	beq- cr7, 1f
 	#3) else: we must call pthread_sigmask(SIG_SETMASK, 0, (sigset_t *)buf->__ss);
-	# increase stack frame by 16
-	subi 1, 1, 16
-	# thus store r3 on the stack, to restore it later
-	stw 3, 12(1)
-	# store old link reg
-	mflr 0
-	stw 0, 8(1)
+	# store non-volatile regs 30, 31 into the setjmp buf
+	stw 30, 0(3)
+	stw 31, 4(3)
+	# use them to store the pointer to the jmpbuf and the link reg
+	mr 30, 3
+	mflr 31
+	
 	# put pointer to ss buf into r5 (3rd arg)
 	addi 5, 3, 260
 	# put "2" i.e. SIG_SETMASK in r3
 	li 3, 2
 	li 4, 0
 	bl pthread_sigmask
-	#restore r3
-	lwz 3, 12(1)
-	#restore link reg
-	lwz 0, 8(1)
-	mtlr 0
-	#restore sp
-	addi 1, 1, 16
+	
+	#restore jmpbuf pointer and link reg
+	mr 3, 30
+	mtlr 31
+	#resore non-volatile regs
+	lwz 30, 0(3)
+	lwz 31, 4(3)
+
 1:
 	b setjmp

src/thread/powerpc/clone.s

@@ -13,12 +13,10 @@ __clone:
 # SYS_clone = 120
 # SYS_exit = 1
 
-# in order that the child can find the start func and its arg, we need to store it into
-# non-volative regs. to do so, we have to store those 2 regs into our stackframe, so
-# we can restore them later.
-subi 1, 1, 16 
-stw 30, 12(1)
-stw 31, 8(1)
+# store non-volatile regs r30, r31 on stack in order to put our
+# start func and its arg there
+stwu 30, -16(1)
+stw 31, 4(1)
 
 # save r3 (func) into r30, and r6(arg) into r31
 mr 30, 3
@@ -37,19 +35,9 @@ li 0, 120
 sc
 
 # check for syscall error
-#this code should be more efficient, but it borks
-#bns+ 1f # jump to label 1 if no summary overflow.
+bns+ 1f # jump to label 1 if no summary overflow.
 #else
-#neg 3, 3 #negate the result (errno)
-#b 2f # jump to epilogue
-
-# this error check code at least does not spoil the clone call.
-#mfcr    0                      # Check for an error
-#rlwinm  4, 0, 0, 3, 3        # by checking for bit 28.
-#cmplwi  0, 4, 0               # It is an error if non-zero.
-#beq     0, 1f                  # Jump if not an error.
-#neg     3, 3                  # Negate the error number.
-#b       2f # jump to epilogue
+neg 3, 3 #negate the result (errno)
 1:
 # compare sc result with 0
 cmpwi cr7, 3, 0
@@ -58,8 +46,7 @@ cmpwi cr7, 3, 0
 bne cr7, 2f
 
 #else: we're the child
-#call funcptr
-# move arg (d) into r3
+#call funcptr: move arg (d) into r3
 mr 3, 31
 #move r30 (funcptr) into CTR reg
 mtctr 30
@@ -72,12 +59,9 @@ sc
 2:
 
 # restore stack
-lwz 30, 12(1)
-lwz 31, 8(1)
+lwz 30, 0(1)
+lwz 31, 4(1)
 addi 1, 1, 16
 
 blr
 
-
-
-