arch/m68k/include/asm/switch_to.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _M68K_SWITCH_TO_H
   3 #define _M68K_SWITCH_TO_H
   4
   5 /*
   6  * switch_to(n) should switch tasks to task ptr, first checking that
   7  * ptr isn't the current task, in which case it does nothing.  This
   8  * also clears the TS-flag if the task we switched to has used the
   9  * math co-processor latest.
  10  */
  11 /*
  12  * switch_to() saves the extra registers, that are not saved
  13  * automatically by SAVE_SWITCH_STACK in resume(), ie. d0-d5 and
  14  * a0-a1. Some of these are used by schedule() and its predecessors
  15  * and so we might get see unexpected behaviors when a task returns
  16  * with unexpected register values.
  17  *
  18  * syscall stores these registers itself and none of them are used
  19  * by syscall after the function in the syscall has been called.
  20  *
  21  * Beware that resume now expects *next to be in d1 and the offset of
  22  * tss to be in a1. This saves a few instructions as we no longer have
  23  * to push them onto the stack and read them back right after.
  24  *
  25  * 02/17/96 - Jes Sorensen (jds@kom.auc.dk)
  26  *
  27  * Changed 96/09/19 by Andreas Schwab
  28  * pass prev in a0, next in a1
  29  */
  30 asmlinkage void resume(void);
  31 #define switch_to(prev,next,last) do { \
  32   register void *_prev __asm__ ("a0") = (prev); \
  33   register void *_next __asm__ ("a1") = (next); \
  34   register void *_last __asm__ ("d1"); \
  35   __asm__ __volatile__("jbsr resume" \
  36                        : "=a" (_prev), "=a" (_next), "=d" (_last) \
  37                        : "0" (_prev), "1" (_next) \
  38                        : "d0", "d2", "d3", "d4", "d5"); \
  39   (last) = _last; \
  40 } while (0)
  41
  42 #endif /* _M68K_SWITCH_TO_H */