From: Tormod Volden <debian.tormod@gmail.com>
Date: Thu, 16 Apr 2015 22:00:18 +0000 (+0200)
Subject: 6809: Adjust syscall argument passing to caller convention
X-Git-Url: https://git.ndcode.org/public/gitweb.cgi?a=commitdiff_plain;h=4851846370a543194678533ee64d645504b9b326;p=FUZIX.git

6809: Adjust syscall argument passing to caller convention

The calling user process will put the first argument in
X and the rest on the stack. Make sure this get carried over
to u_argn etc correctly.

Also make sure the return values from the system call is
handed back to the caller through the rti.

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

diff --git a/Kernel/lowlevel-6809.s b/Kernel/lowlevel-6809.s
index 30e9c406..6d338d7c 100644
--- a/Kernel/lowlevel-6809.s
+++ b/Kernel/lowlevel-6809.s
@@ -75,26 +75,26 @@ unix_syscall_entry:
 	lda #1
 	sta _kernel_flag
 
-	leax 12,s	; stacked by the swi
+	leax 14,s	; 12 stacked by the swi + return address of caller
 	ldy #U_DATA__U_ARGN
 	SAM_USER
-	ldd ,x++	; copy arguments
+	ldd 4,s		; first argument in swi stacked X
 	SAM_KERNEL
 	std ,y++
 	SAM_USER
-	ldd ,x++
+	ldd ,x++	; second argument from caller's stack
 	SAM_KERNEL
 	std ,y++
 	SAM_USER
-	ldd ,x++
+	ldd ,x++ 	; third
 	SAM_KERNEL
 	std ,y++
 	SAM_USER
-	ldd ,x++
+	ldd ,x++ 	; fourth
 	SAM_KERNEL
 	std ,y++
 	SAM_USER
-	ldd 4,s		; X register -> syscall number
+	ldd 1,s		; stacked D register -> syscall number
 	SAM_KERNEL
 	stb U_DATA__U_CALLNO
         ; save process stack pointer (in user page)
@@ -140,10 +140,14 @@ unix_syscall_entry:
 not_error:
         ; no error to signal! return syscall return value instead of error code
         ldx U_DATA__U_RETVAL
-	ldd #0
+	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 510d5783..a8c906da 100644
--- a/Library/libs/fuzix6809/syscall6809.s
+++ b/Library/libs/fuzix6809/syscall6809.s
@@ -8,8 +8,5 @@ __syscall:
 	bne	error
 	rts
 error:
-	sta	_errno
-	ldx	#0
-	stx	_errno+1
-	leax	-1,x		; Return $FFFF (-1)
+	std	_errno		; X is -1
 	rts
diff --git a/Library/tools/syscall_6809.c b/Library/tools/syscall_6809.c
index 64a05774..f310978c 100644
--- a/Library/tools/syscall_6809.c
+++ b/Library/tools/syscall_6809.c
@@ -21,7 +21,7 @@ static void write_call(int n)
   fprintf(fp, "\t.area .text\n\n");
   fprintf(fp, "\t.globl __syscall\n");
   fprintf(fp, "\t.globl _%s\n\n", syscall_name[n]);
-  fprintf(fp, "_%s:\n\tldx #%d\n", syscall_name[n], n);
+  fprintf(fp, "_%s:\n\tldd #%d\n", syscall_name[n], n);
   fprintf(fp, "\tjmp __syscall\n");
   fclose(fp);
 }