arch/arc/kernel/ctx_sw.c

   1 /*
   2  * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  *
   8  * Vineetg: Aug 2009
   9  *  -"C" version of lowest level context switch asm macro called by schedular
  10  *   gcc doesn't generate the dward CFI info for hand written asm, hence can't
  11  *   backtrace out of it (e.g. tasks sleeping in kernel).
  12  *   So we cheat a bit by writing almost similar code in inline-asm.
  13  *  -This is a hacky way of doing things, but there is no other simple way.
  14  *   I don't want/intend to extend unwinding code to understand raw asm
  15  */
  16
  17 #include <asm/asm-offsets.h>
  18 #include <linux/sched.h>
  19
  20 #define KSP_WORD_OFF    ((TASK_THREAD + THREAD_KSP) / 4)
  21
  22 struct task_struct *__sched
  23 __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
  24 {
  25         unsigned int tmp;
  26         unsigned int prev = (unsigned int)prev_task;
  27         unsigned int next = (unsigned int)next_task;
  28
  29         __asm__ __volatile__(
  30                 /* FP/BLINK save generated by gcc (standard function prologue */
  31                 "st.a    r13, [sp, -4]   \n\t"
  32                 "st.a    r14, [sp, -4]   \n\t"
  33                 "st.a    r15, [sp, -4]   \n\t"
  34                 "st.a    r16, [sp, -4]   \n\t"
  35                 "st.a    r17, [sp, -4]   \n\t"
  36                 "st.a    r18, [sp, -4]   \n\t"
  37                 "st.a    r19, [sp, -4]   \n\t"
  38                 "st.a    r20, [sp, -4]   \n\t"
  39                 "st.a    r21, [sp, -4]   \n\t"
  40                 "st.a    r22, [sp, -4]   \n\t"
  41                 "st.a    r23, [sp, -4]   \n\t"
  42                 "st.a    r24, [sp, -4]   \n\t"
  43 #ifndef CONFIG_ARC_CURR_IN_REG
  44                 "st.a    r25, [sp, -4]   \n\t"
  45 #else
  46                 "sub     sp, sp, 4      \n\t"   /* usual r25 placeholder */
  47 #endif
  48
  49                 /* set ksp of outgoing task in tsk->thread.ksp */
  50 #if KSP_WORD_OFF <= 255
  51                 "st.as   sp, [%3, %1]    \n\t"
  52 #else
  53                 /*
  54                  * Workaround for NR_CPUS=4k
  55                  * %1 is bigger than 255 (S9 offset for st.as)
  56                  */
  57                 "add2    r24, %3, %1     \n\t"
  58                 "st      sp, [r24]       \n\t"
  59 #endif
  60
  61                 /*
  62                  * setup _current_task with incoming tsk.
  63                  * optionally, set r25 to that as well
  64                  * For SMP extra work to get to &_current_task[cpu]
  65                  * (open coded SET_CURR_TASK_ON_CPU)
  66                  */
  67 #ifndef CONFIG_SMP
  68                 "st  %2, [@_current_task]       \n\t"
  69 #else
  70                 "lr   r24, [identity]           \n\t"
  71                 "lsr  r24, r24, 8               \n\t"
  72                 "bmsk r24, r24, 7               \n\t"
  73                 "add2 r24, @_current_task, r24  \n\t"
  74                 "st   %2,  [r24]                \n\t"
  75 #endif
  76 #ifdef CONFIG_ARC_CURR_IN_REG
  77                 "mov r25, %2   \n\t"
  78 #endif
  79
  80                 /* get ksp of incoming task from tsk->thread.ksp */
  81                 "ld.as  sp, [%2, %1]   \n\t"
  82
  83                 /* start loading it's CALLEE reg file */
  84
  85 #ifndef CONFIG_ARC_CURR_IN_REG
  86                 "ld.ab   r25, [sp, 4]   \n\t"
  87 #else
  88                 "add    sp, sp, 4       \n\t"
  89 #endif
  90                 "ld.ab   r24, [sp, 4]   \n\t"
  91                 "ld.ab   r23, [sp, 4]   \n\t"
  92                 "ld.ab   r22, [sp, 4]   \n\t"
  93                 "ld.ab   r21, [sp, 4]   \n\t"
  94                 "ld.ab   r20, [sp, 4]   \n\t"
  95                 "ld.ab   r19, [sp, 4]   \n\t"
  96                 "ld.ab   r18, [sp, 4]   \n\t"
  97                 "ld.ab   r17, [sp, 4]   \n\t"
  98                 "ld.ab   r16, [sp, 4]   \n\t"
  99                 "ld.ab   r15, [sp, 4]   \n\t"
 100                 "ld.ab   r14, [sp, 4]   \n\t"
 101                 "ld.ab   r13, [sp, 4]   \n\t"
 102
 103                 /* last (ret value) = prev : although for ARC it mov r0, r0 */
 104                 "mov     %0, %3        \n\t"
 105
 106                 /* FP/BLINK restore generated by gcc (standard func epilogue */
 107
 108                 : "=r"(tmp)
 109                 : "n"(KSP_WORD_OFF), "r"(next), "r"(prev)
 110                 : "blink"
 111         );
 112
 113         return (struct task_struct *)tmp;
 114 }