arch/m68k/include/asm/switch_to.h

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