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 30e9c40..6d338d7 100644 (file)
--- 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 510d578..a8c906d 100644 (file)
--- 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 64a0577..f310978 100644 (file)
--- 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);
 }