arch/h8300/include/asm/switch_to.h

   1 #ifndef _H8300_SWITCH_TO_H
   2 #define _H8300_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, offset of tss in d1, and whether
  28  * the mm structures are shared in d2 (to avoid atc flushing).
  29  *
  30  * H8/300 Porting 2002/09/04 Yoshinori Sato
  31  */
  32
  33 asmlinkage void resume(void);
  34 #define switch_to(prev, next, last) \
  35 do {                         \
  36         void *_last;                                        \
  37         __asm__ __volatile__(                               \
  38                 "mov.l  %1, er0\n\t"                        \
  39                 "mov.l  %2, er1\n\t"                        \
  40                 "mov.l  %3, er2\n\t"                        \
  41                 "jsr @_resume\n\t"                          \
  42                 "mov.l  er2,%0\n\t"                         \
  43                 : "=r" (_last)                              \
  44                 : "r" (&(prev->thread)),                    \
  45                   "r" (&(next->thread)),                    \
  46                   "g" (prev)                                \
  47                 : "cc", "er0", "er1", "er2", "er3");        \
  48         (last) = _last;                                     \
  49 } while (0)
  50
  51 #endif /* _H8300_SWITCH_TO_H */