/*
            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)
*/

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.text
.globl _ostd_make_fcontext
_ostd_make_fcontext:
    ; save return address into R6
    mflr  r6

    ; first arg of ostd_make_fcontext() == top address of context-function
    ; shift address in R3 to lower 16 byte boundary
    clrrwi  r3, r3, 4

    ; reserve space for context-data on context-stack
    ; including 64 byte of linkage + parameter area (R1  16 == 0)
    subi  r3, r3, 248

    ; third arg of ostd_make_fcontext() == address of context-function
    stw  r5, 176(r3)

    ; set back-chain to zero
    li   %r0, 0
    std  %r0, 184(%r3)

    ; compute address of returned transfer_t
    addi %r0, %r3, 232
    mr   %r4, %r0
    std  %r4, 152(%r3)

    ; load LR
    mflr  r0
    ; jump to label 1
    bl  l1
l1:
    ; load LR into R4
    mflr  r4
    ; compute abs address of label finish
    addi  r4, r4, lo16((finish - .) + 4)
    ; restore LR
    mtlr  r0
    ; save address of finish as return-address for context-function
    ; will be entered after context-function returns
    std  r4, 168(r3)

    ; restore return address from R6
    mtlr  r6

    blr  ; return pointer to context-data

finish:
    ; save return address into R0
    mflr  r0
    ; save return address on stack, set up stack frame
    stw  r0, 8(r1)
    ; allocate stack space, R1  16 == 0
    stwu  r1, -32(r1)

    ; set return value to zero
    li  r3, 0
    ; exit application
    bl  __exit
    nop