From: Tormod Volden <debian.tormod@gmail.com>
Date: Sun, 17 May 2015 16:38:34 +0000 (+0200)
Subject: lowlevel-6809: Do not clobber CC on syscall SWI exit
X-Git-Url: https://git.ndcode.org/public/gitweb.cgi?a=commitdiff_plain;h=ad2737755ec6e37e3f060eced77b44b7254bb4a1;p=FUZIX.git

lowlevel-6809: Do not clobber CC on syscall SWI exit

In particular the interrupt masks were overwritten and in some
cases interrupts were disabled after returning from a syscall.

Rewrite the SWI interface to only report error through D and X.

Signed-off-by: Tormod Volden <debian.tormod@gmail.com>
---

diff --git a/Kernel/lowlevel-6809.s b/Kernel/lowlevel-6809.s
index 899b20d8..a4d8ace5 100644
--- a/Kernel/lowlevel-6809.s
+++ b/Kernel/lowlevel-6809.s
@@ -140,14 +140,11 @@ unix_syscall_entry:
 not_error:
         ; no error to signal! return syscall return value instead of error code
         ldx U_DATA__U_RETVAL
-	ldd #0		; just for setting Z flag
 unix_return:
 	; we never make a syscall from in kernel space
 	SAM_USER
 	stx 4,s		; replace stacked values before rti
 	std 1,s
-	tfr cc,a	; Z determined by D
-	sta ,s		; replace stacked CC to signal error
 	rti
 
 ;
diff --git a/Library/libs/fuzix6809/syscall6809.s b/Library/libs/fuzix6809/syscall6809.s
index 0f284d37..55100424 100644
--- a/Library/libs/fuzix6809/syscall6809.s
+++ b/Library/libs/fuzix6809/syscall6809.s
@@ -6,19 +6,20 @@
 
 __syscall:
 	swi
-	bne	error
-	rts
-error:
-	std	_errno		; X is -1
+	cmpd #0			; D holds errno, if any
+	beq @noerr
+	std _errno		; X is -1 in this case
+@noerr:
 	rts
 
 ; for variadic functions:
 ; compensate for the 1st argument that we removed
 __syscall_mangled:
 	swi
-	beq	noerr
-	std	_errno
-noerr:
+	cmpd #0
+	beq @noerr
+	std _errno
+@noerr:
 	puls d		; get return address
-	pshs d,x	; inject a word on stack
+	pshs d,x	; inject a word on stack, e.g. X
 	rts