/*
            Copyright Oliver Kowalke 2009.
   Distributed under the Boost Software License, Version 1.0.
      (See accompanying file LICENSE_1_0.txt or copy at
          http://www.boost.org/LICENSE_1_0.txt)
*/

/*******************************************************
 *                                                     *
 *  -------------------------------------------------  *
 *  |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |  *
 *  -------------------------------------------------  *
 *  |  0  |  4  |  8  |  12 |  16 |  20 |  24 |  28 |  *
 *  -------------------------------------------------  *
 *  |    R13    |    R14    |    R15    |    R16    |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  8  |  9  |  10 |  11 |  12 |  13 |  14 |  15 |  *
 *  -------------------------------------------------  *
 *  |  32 |  36 |  40 |  44 |  48 |  52 |  56 |  60 |  *
 *  -------------------------------------------------  *
 *  |    R17    |    R18    |     R19   |    R20    |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  16 |  17 |  18 |  19 |  20 |  21 |  22 |  23 |  *
 *  -------------------------------------------------  *
 *  |  64 |  68 |  72 |  76 |  80 |  84 |  88 |  92 |  *
 *  -------------------------------------------------  *
 *  |    R21    |    R22    |    R23    |    R24    |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  24 |  25 |  26 |  27 |  28 |  29 |  30 |  31 |  *
 *  -------------------------------------------------  *
 *  |  96 | 100 | 104 | 108 | 112 | 116 | 120 | 124 |  *
 *  -------------------------------------------------  *
 *  |    R25    |    R26    |    R27    |    R28    |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  32 |  33 |  34 |  35 |  36 |  37 |  38 |  39 |  *
 *  -------------------------------------------------  *
 *  | 128 | 132 | 136 | 140 | 144 | 148 | 152 | 156 |  *
 *  -------------------------------------------------  *
 *  |    R29    |    R30    |    R31    |   hidden  |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  40 |  41 |  42 |  43 |  44 |  45 |  46 |  47 |  *
 *  -------------------------------------------------  *
 *  | 160 | 164 | 168 | 172 | 176 | 180 | 184 | 188 |  *
 *  -------------------------------------------------  *
 *  |     CR    |     LR    |     PC    | back-chain|  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  48 |  49 |  50 |  51 |  52 |  53 |  54 |  55 |  *
 *  -------------------------------------------------  *
 *  | 192 | 196 | 200 | 204 | 208 | 212 | 216 | 220 |  *
 *  -------------------------------------------------  *
 *  |  cr saved |  lr saved |  compiler |   linker  |  *
 *  -------------------------------------------------  *
 *  -------------------------------------------------  *
 *  |  56 |  57 |  58 |  59 |  60 |  61 |  62 |  63 |  *
 *  -------------------------------------------------  *
 *  | 224 | 228 | 232 | 236 | 240 | 244 | 248 | 252 |  *
 *  -------------------------------------------------  *
 *  |    FCTX   |    DATA   |           |           |  *
 *  -------------------------------------------------  *
 *                                                     *
 *******************************************************/

.text
.align 2
.globl _jump_fcontext

_jump_fcontext:
    ; reserve space on stack
    subi  r1, r1, 184

    std  r14, 8(r1)  ; save R14
    std  r15, 16(r1)  ; save R15
    std  r16, 24(r1)  ; save R16
    std  r17, 32(r1)  ; save R17
    std  r18, 40(r1)  ; save R18
    std  r19, 48(r1)  ; save R19
    std  r20, 56(r1)  ; save R20
    std  r21, 64(r1)  ; save R21
    std  r22, 72(r1)  ; save R22
    std  r23, 80(r1)  ; save R23
    std  r24, 88(r1)  ; save R24
    std  r25, 96(r1)  ; save R25
    std  r26, 104(r1)  ; save R26
    std  r27, 112(r1)  ; save R27
    std  r28, 120(r1)  ; save R28
    std  r29, 128(r1)  ; save R29
    std  r30, 136(r1)  ; save R30
    std  r31, 144(r1)  ; save R31
    std  r3,  152(r1)  ; save hidden

    ; save CR
    mfcr  r0
    std   r0, 160(r1)
    ; save LR
    mflr  r0
    std   r0, 168(r1)
    ; save LR as PC
    std   r0, 176(r1)

    ; store RSP (pointing to context-data) in R6
    mr  r6, r1

    ; restore RSP (pointing to context-data) from R4
    mr  r1, r4

    ld  r14, 8(r1)  ; restore R14
    ld  r15, 16(r1)  ; restore R15
    ld  r16, 24(r1)  ; restore R16
    ld  r17, 32(r1)  ; restore R17
    ld  r18, 40(r1)  ; restore R18
    ld  r19, 48(r1)  ; restore R19
    ld  r20, 56(r1)  ; restore R20
    ld  r21, 64(r1)  ; restore R21
    ld  r22, 72(r1)  ; restore R22
    ld  r23, 80(r1)  ; restore R23
    ld  r24, 88(r1)  ; restore R24
    ld  r25, 96(r1)  ; restore R25
    ld  r26, 104(r1)  ; restore R26
    ld  r27, 112(r1)  ; restore R27
    ld  r28, 120(r1)  ; restore R28
    ld  r29, 128(r1)  ; restore R29
    ld  r30, 136(r1)  ; restore R30
    ld  r31, 144(r1)  ; restore R31
    ld  r3,  152(r1)  ; restore hidden

    ; restore CR
    ld  r0, 160(r1)
    mtcr  r0
    ; restore LR
    ld  r0, 168(r1)
    mtlr  r0

    ; load PC
    ld  r12, 176(r1)
    ; restore CTR
    mtctr  r12

    ; adjust stack
    addi  r1, r1, 184

    ; zero in r3 indicates first jump to context-function
    cmpdi r3, 0
    beq use_entry_arg

    ; return transfer_t
    std  r6, 0(r3)
    std  r5, 8(r3)

    ; jump to context
    bctr

use_entry_arg:
    ; copy transfer_t into transfer_fn arg registers
    mr  r3, r6
    mr  r4, r5

    ; jump to context
    bctr