68000-softmmu: first guess at fork()

diff --git a/Kernel/platform-v68-softmmu/tricks.S b/Kernel/platform-v68-softmmu/tricks.S
index 0175d60..94c7609 100644 (file)
--- a/Kernel/platform-v68-softmmu/tricks.S
+++ b/Kernel/platform-v68-softmmu/tricks.S
@@ -97,43 +97,87 @@ switchinfail:
        ; 4(sp) = child process table entry
        ;
        ; Exit:
-       ; We are running as the child, A5 = u_data pointer of child, on
-       ; child stack and leap directly back to user mode
+       ; We are running as the parent, A5 = u_data pointer of parent.
        ;
 dofork:
-       moveq #-1,d0
-       rts
        ;
-       ; We need the child to return off its own stack so this is very
-       ; different to other platforms.
+       ; On a flat_mem system the software MMU already cloned the memory
+       ; map except that the child is not currently identity mapped. The
+       ; parent will return via its copy of the udata, but the child udata
+       ; is not mapped at the same address so we must build the child a
+       ; fake task switch frame that returns to user space.
        ;
        move.l 4(sp),a0                 ;       child p_tab
-       ;
-       ; in the simple case we only have one udata. In the complex cases
-       ; we would have to compute the new one and load it into a5 and
-       ; offset
+
+       move.l P_TAB__P_UDATA(a0),a1    ;       child udata
 
        ;
-       ; Set up a switchin frame for the parent process
+       ; Copy the parent udata into the child. Only copy the struct data.
+       ; Probably not worth saving registers and using movem to speed up.
        ;
-       move.w P_TAB__P_PID_OFFSET(a0),-(sp)    ;       child pid (parent return)
-       move.l usp,a0
-       movem.l a0/a2-a4/a6/d2-d7,-(sp) ;       save state
-       move.l sp,U_DATA__U_SP(a5)      ;       save pointer
 
-       move.l a0,-(sp)                 ;       argument to newproc
-       move.w P_TAB__P_PAGE_OFFSET(a0),d0      ; page
+       movem.l a1/a5,-(sp)
+       moveq #U_DATA_COPYSIZE-1,d0
+cplp:
+       move.l (a5)+,(a1)+
+       dbra d0,cplp
+
+       movem.l (sp)+,a1/a5
 
-;      jsr bankfork                    ;       copy the memory
 
-       move.l (sp),a0
+       lea.l a0,512(a1)                ;       top of child kernel stack
+
+       ;
+       ; Stack a task switch frame into a1
+       ;
+
+       move.l 508(a5),-(a0)            ;       trap frame
+       move.l 504(a5),-(a0)            ;        ""    ""
+       move.l 500(a5),-(a0)            ;       A5
+       move.l #child_rte,-(a0)         ;       under the 3 copied words
+       movem.l a0/a2-a4/a6/d2-d7,-(a0) ;       the faked switchin frame
+       move.l a0,U_DATA__U_SP(a1)      ;       set child frame pointer
+
+       ;
+       ; Now finish up the process creation
+       ;
+       move.l  a5,-(sp)                ;       save true udata
+       move.l P_TAB_P__UDATA(a1),a5    ;       child
+       move.l a5,udata_shadow          ;       paranoia
        
        jsr newproc                     ;       Called with the child udata
-       add.w #54,sp                    ;       toss the stack frames
 
-       clr.w runticks
-       moveq #0,d0                     ;       child
-       rts
+       move.l U_DATA__U_PTAB(a5),a1    ;       reload child pptr
+       move.w P_TAB__P_PID(a1),d0      ;       pid of child
+       ext.l d0
+       move.l (sp)+, a5                ;       recover parent udata
+       move.l a5,udata_shadow          ;       paranoia
+       rts                             ;       return as parent
+
+;
+;      This is called with the faked stack frame from dofork. All we have
+;      on the stack is the A5 to restore and the fake stack frame. All the
+;      other register restores will be done via the fork() syscall code in
+;      userspace. The child returns this way not via syscall paths.
+;
+child_rte:
+       move.l (sp)+,a5
+       moveq #0,d0
+       move.l d0,d1
+       move.l d1,d2
+       move.l d2,d3
+       move.l d3,d4
+       move.l d4,d5
+       move.l d5,d6
+       move.l d6,d7
+       move.l d7,a0
+       move.l a0,a1
+       move.l a1,a2
+       move.l a2,a3
+       move.l a3,a4
+       move.l a4,a6
+       rte
+
 
 badswitchmsg: ascii "_switchin: FAIL"
             byte 13,10,0