/*      $NetBSD: reenter_syscall.s,v 1.7 2021/02/23 16:54:17 tsutsui Exp $      */

/*
 * Written by ITOH Yasufumi.
 * Public domain.
 */

#include <m68k/asm.h>
#include "assym.h"

/*
 * void reenter_syscall(struct frame *fp, int stkadj)
 *                                      __attribute__((__noreturn__));
 *
 * Move stack frame by stkadj bytes and re-enter syscall().
 *
 * XXX This is a kludge.
 */

ENTRY_NOPROFILE(reenter_syscall)
        addql   #4,%sp                  | pop PC
        movel   (%sp)+,%a0              | current frame addr
        movel   (%sp),%d1               | stkadj

| The m68k frame (struct trapframe) format:
|       16:l    d0-d7/a0-a6/usp
|       1:w     (pad)
|       1:w     stkadj
|       1:w     sr
|       1:l     pc
|       1:w     format/vector

        moveal  %a0,%a1
        subal   %d1,%a1                 | new frame address
        moveal  %a1,%sp                 | set SP

        | copy down frame (16*4 + 2 + 2 + 2 + 4 + 2 = 76 bytes = 19 longs)
        moveq   #19-1,%d0
.Lcpfr: movel   (%a0)+,(%a1)+
        dbra    %d0,.Lcpfr

        movew   %d1,FR_ADJ(%sp)         | set stack adjust count
        movel   (%sp),-(%sp)            | push syscall no (original d0 value)
        jbsr    _C_LABEL(syscall)       | re-enter syscall()
        addql   #4,%sp                  | pop syscall no
#ifdef DEBUG
        tstw    FR_ADJ(%sp)             | stack adjust must be zero
        jeq     .Ladjzero
        PANIC("reenter_syscall")
.Ladjzero:
#endif
        moveal  FR_SP(%sp),%a0          | grab and restore
        movel   %a0,%usp                |   user SP
        movw    FR_ADJ(%sp),%d0         | need to adjust stack?
        jne     .Ladjstk                | yes, go to it
        moveml  (%sp)+,#0x7FFF          | restore user registers
        addql   #8,%sp                  | pop SP and stack adjust
        jra     _ASM_LABEL(rei)         | rte
.Ladjstk:
        lea     FR_HW(%sp),%a1          | pointer to HW frame
        addql   #8,%a1                  | source pointer
        movl    %a1,%a0                 | source
        addw    %d0,%a0                 |  + hole size = dest pointer
        movl    -(%a1),-(%a0)           | copy
        movl    -(%a1),-(%a0)           |  8 bytes
        movl    %a0,FR_SP(%sp)          | new SSP
        moveml  (%sp)+,#0x7FFF          | restore user register
        movl    (%sp),%sp               | and do real RTE
        jra     _ASM_LABEL(rei)         | rte