65c816: fix wrap on DP computation, and add brk handling

diff --git a/Kernel/lowlevel-65c816.s b/Kernel/lowlevel-65c816.s
index 355c5d5..d98c5f4 100644 (file)
--- a/Kernel/lowlevel-65c816.s
+++ b/Kernel/lowlevel-65c816.s
@@ -8,6 +8,7 @@
        .export map_process_always
        .export map_kernel
        .export _userpage
+       .export _brk_limit
 
        .export sigret_irq
        .export sigret
@@ -116,6 +117,7 @@ setdp:
        adc     #STACK_BANKOFF          ; we now point at the stack
        inc     a                       ; plus 0x100
        xba                             ; Swap to get xx00 format we need
+       and     #$FF00                  ; remove any carry bits
        tcd
        pla
 
@@ -362,10 +364,33 @@ signal_out:
        cli
        rtl                     ;       return into user app handler
 ;
+;
+;      Helper for brk(). In this case we need it in asm to deal with the
+;      strange dual stack setup
+;
+_brk_limit:
+       .a8
+       .i8
+       rep #$10
+       .i16
+       ldx U_DATA__U_SYSCALL_SP
+       lda f:2,x
+       tax
+       lda f:1,x
+       dex
+       dex
+       dex                             ; allow 384 bytes headroom
+       sep #$10
+       .i8
+       rts
+
+;
 ;      doexec is a special case syscall exit path. Set up the bank
 ;      registers and return directly to the start of the user process
 ;
 _doexec:
+       .a8
+       .i8
        sta     ptr1
        stx     ptr1+1          ;       address to execute from
        sei
@@ -1011,5 +1036,5 @@ sigret_irq:
        .i8
 
 syscall_vector:
-       jsl     KERNEL_FAR+syscall_entry
+       jsl     KERNEL_CODE_FAR+syscall_entry
        rts