arch/sh64/kernel/switchto.S

   1 /*
   2  * arch/sh64/kernel/switchto.S
   3  *
   4  * sh64 context switch
   5  *
   6  * Copyright (C) 2004  Richard Curnow
   7  *
   8  * This file is subject to the terms and conditions of the GNU General Public
   9  * License.  See the file "COPYING" in the main directory of this archive
  10  * for more details.
  11 */
  12
  13         .section .text..SHmedia32,"ax"
  14         .little
  15
  16         .balign 32
  17
  18         .type sh64_switch_to,@function
  19         .global sh64_switch_to
  20         .global __sh64_switch_to_end
  21 sh64_switch_to:
  22
  23 /* Incoming args
  24    r2 - prev
  25    r3 - &prev->thread
  26    r4 - next
  27    r5 - &next->thread
  28
  29    Outgoing results
  30    r2 - last (=prev) : this just stays in r2 throughout
  31
  32    Want to create a full (struct pt_regs) on the stack to allow backtracing
  33    functions to work.  However, we only need to populate the callee-save
  34    register slots in this structure; since we're a function our ancestors must
  35    have themselves preserved all caller saved state in the stack.  This saves
  36    some wasted effort since we won't need to look at the values.
  37
  38    In particular, all caller-save registers are immediately available for
  39    scratch use.
  40
  41 */
  42
  43 #define FRAME_SIZE (76*8 + 8)
  44
  45         movi    FRAME_SIZE, r0
  46         sub.l   r15, r0, r15
  47         ! Do normal-style register save to support backtrace
  48
  49         st.l    r15,   0, r18   ! save link reg
  50         st.l    r15,   4, r14   ! save fp
  51         add.l   r15, r63, r14   ! setup frame pointer
  52
  53         ! hopefully this looks normal to the backtrace now.
  54
  55         addi.l  r15,   8, r1    ! base of pt_regs
  56         addi.l  r1,   24, r0    ! base of pt_regs.regs
  57         addi.l  r0, (63*8), r8  ! base of pt_regs.trregs
  58
  59         /* Note : to be fixed?
  60            struct pt_regs is really designed for holding the state on entry
  61            to an exception, i.e. pc,sr,regs etc.  However, for the context
  62            switch state, some of this is not required.  But the unwinder takes
  63            struct pt_regs * as an arg so we have to build this structure
  64            to allow unwinding switched tasks in show_state() */
  65
  66         st.q    r0, ( 9*8), r9
  67         st.q    r0, (10*8), r10
  68         st.q    r0, (11*8), r11
  69         st.q    r0, (12*8), r12
  70         st.q    r0, (13*8), r13
  71         st.q    r0, (14*8), r14 ! for unwind, want to look as though we took a trap at
  72         ! the point where the process is left in suspended animation, i.e. current
  73         ! fp here, not the saved one.
  74         st.q    r0, (16*8), r16
  75
  76         st.q    r0, (24*8), r24
  77         st.q    r0, (25*8), r25
  78         st.q    r0, (26*8), r26
  79         st.q    r0, (27*8), r27
  80         st.q    r0, (28*8), r28
  81         st.q    r0, (29*8), r29
  82         st.q    r0, (30*8), r30
  83         st.q    r0, (31*8), r31
  84         st.q    r0, (32*8), r32
  85         st.q    r0, (33*8), r33
  86         st.q    r0, (34*8), r34
  87         st.q    r0, (35*8), r35
  88
  89         st.q    r0, (44*8), r44
  90         st.q    r0, (45*8), r45
  91         st.q    r0, (46*8), r46
  92         st.q    r0, (47*8), r47
  93         st.q    r0, (48*8), r48
  94         st.q    r0, (49*8), r49
  95         st.q    r0, (50*8), r50
  96         st.q    r0, (51*8), r51
  97         st.q    r0, (52*8), r52
  98         st.q    r0, (53*8), r53
  99         st.q    r0, (54*8), r54
 100         st.q    r0, (55*8), r55
 101         st.q    r0, (56*8), r56
 102         st.q    r0, (57*8), r57
 103         st.q    r0, (58*8), r58
 104         st.q    r0, (59*8), r59
 105
 106         ! do this early as pta->gettr has no pipeline forwarding (=> 5 cycle latency)
 107         ! Use a local label to avoid creating a symbol that will confuse the !
 108         ! backtrace
 109         pta     .Lsave_pc, tr0
 110
 111         gettr   tr5, r45
 112         gettr   tr6, r46
 113         gettr   tr7, r47
 114         st.q    r8, (5*8), r45
 115         st.q    r8, (6*8), r46
 116         st.q    r8, (7*8), r47
 117
 118         ! Now switch context
 119         gettr   tr0, r9
 120         st.l    r3, 0, r15      ! prev->thread.sp
 121         st.l    r3, 8, r1       ! prev->thread.kregs
 122         st.l    r3, 4, r9       ! prev->thread.pc
 123         st.q    r1, 0, r9       ! save prev->thread.pc into pt_regs->pc
 124
 125         ! Load PC for next task (init value or save_pc later)
 126         ld.l    r5, 4, r18      ! next->thread.pc
 127         ! Switch stacks
 128         ld.l    r5, 0, r15      ! next->thread.sp
 129         ptabs   r18, tr0
 130
 131         ! Update current
 132         ld.l    r4, 4, r9       ! next->thread_info (2nd element of next task_struct)
 133         putcon  r9, kcr0        ! current = next->thread_info
 134
 135         ! go to save_pc for a reschedule, or the initial thread.pc for a new process
 136         blink   tr0, r63
 137
 138         ! Restore (when we come back to a previously saved task)
 139 .Lsave_pc:
 140         addi.l  r15, 32, r0     ! r0 = next's regs
 141         addi.l  r0, (63*8), r8  ! r8 = next's tr_regs
 142
 143         ld.q    r8, (5*8), r45
 144         ld.q    r8, (6*8), r46
 145         ld.q    r8, (7*8), r47
 146         ptabs   r45, tr5
 147         ptabs   r46, tr6
 148         ptabs   r47, tr7
 149
 150         ld.q    r0, ( 9*8), r9
 151         ld.q    r0, (10*8), r10
 152         ld.q    r0, (11*8), r11
 153         ld.q    r0, (12*8), r12
 154         ld.q    r0, (13*8), r13
 155         ld.q    r0, (14*8), r14
 156         ld.q    r0, (16*8), r16
 157
 158         ld.q    r0, (24*8), r24
 159         ld.q    r0, (25*8), r25
 160         ld.q    r0, (26*8), r26
 161         ld.q    r0, (27*8), r27
 162         ld.q    r0, (28*8), r28
 163         ld.q    r0, (29*8), r29
 164         ld.q    r0, (30*8), r30
 165         ld.q    r0, (31*8), r31
 166         ld.q    r0, (32*8), r32
 167         ld.q    r0, (33*8), r33
 168         ld.q    r0, (34*8), r34
 169         ld.q    r0, (35*8), r35
 170
 171         ld.q    r0, (44*8), r44
 172         ld.q    r0, (45*8), r45
 173         ld.q    r0, (46*8), r46
 174         ld.q    r0, (47*8), r47
 175         ld.q    r0, (48*8), r48
 176         ld.q    r0, (49*8), r49
 177         ld.q    r0, (50*8), r50
 178         ld.q    r0, (51*8), r51
 179         ld.q    r0, (52*8), r52
 180         ld.q    r0, (53*8), r53
 181         ld.q    r0, (54*8), r54
 182         ld.q    r0, (55*8), r55
 183         ld.q    r0, (56*8), r56
 184         ld.q    r0, (57*8), r57
 185         ld.q    r0, (58*8), r58
 186         ld.q    r0, (59*8), r59
 187
 188         ! epilogue
 189         ld.l    r15, 0, r18
 190         ld.l    r15, 4, r14
 191         ptabs   r18, tr0
 192         movi    FRAME_SIZE, r0
 193         add     r15, r0, r15
 194         blink   tr0, r63
 195 __sh64_switch_to_end:
 196 .LFE1:
 197         .size   sh64_switch_to,.LFE1-sh64_switch_to
 198