1;      Copyright Edward Nevill + Oliver Kowalke 2015
2;  Distributed under the Boost Software License, Version 1.0.
3;     (See accompanying file LICENSE_1_0.txt or copy at
4;         http://www.boost.org/LICENSE_1_0.txt)
5
6;*******************************************************
7;*                                                     *
8;*  -------------------------------------------------  *
9;*  |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |  *
10;*  -------------------------------------------------  *
11;*  | 0x0 | 0x4 | 0x8 | 0xc | 0x10| 0x14| 0x18| 0x1c|  *
12;*  -------------------------------------------------  *
13;*  |    d8     |    d9     |    d10    |    d11    |  *
14;*  -------------------------------------------------  *
15;*  -------------------------------------------------  *
16;*  |  8  |  9  |  10 |  11 |  12 |  13 |  14 |  15 |  *
17;*  -------------------------------------------------  *
18;*  | 0x20| 0x24| 0x28| 0x2c| 0x30| 0x34| 0x38| 0x3c|  *
19;*  -------------------------------------------------  *
20;*  |    d12    |    d13    |    d14    |    d15    |  *
21;*  -------------------------------------------------  *
22;*  -------------------------------------------------  *
23;*  |  16 |  17 |  18 |  19 |  20 |  21 |  22 |  23 |  *
24;*  -------------------------------------------------  *
25;*  | 0x40| 0x44| 0x48| 0x4c| 0x50| 0x54| 0x58| 0x5c|  *
26;*  -------------------------------------------------  *
27;*  |    x19    |    x20    |    x21    |    x22    |  *
28;*  -------------------------------------------------  *
29;*  -------------------------------------------------  *
30;*  |  24 |  25 |  26 |  27 |  28 |  29 |  30 |  31 |  *
31;*  -------------------------------------------------  *
32;*  | 0x60| 0x64| 0x68| 0x6c| 0x70| 0x74| 0x78| 0x7c|  *
33;*  -------------------------------------------------  *
34;*  |    x23    |    x24    |    x25    |    x26    |  *
35;*  -------------------------------------------------  *
36;*  -------------------------------------------------  *
37;*  |  32 |  33 |  34 |  35 |  36 |  37 |  38 |  39 |  *
38;*  -------------------------------------------------  *
39;*  | 0x80| 0x84| 0x88| 0x8c| 0x90| 0x94| 0x98| 0x9c|  *
40;*  -------------------------------------------------  *
41;*  |    x27    |    x28    |    FP     |     LR    |  *
42;*  -------------------------------------------------  *
43;*  -------------------------------------------------  *
44;*  |  40 |  41 |  42 |  43 |  44 |  45 |  46 |  47 |  *
45;*  -------------------------------------------------  *
46;*  | 0xa0| 0xa4| 0xa8| 0xac| 0xb0| 0xb4| 0xb8| 0xbc|  *
47;*  -------------------------------------------------  *
48;*  |   base    |   limit   |  dealloc  | fiber data|  *
49;*  -------------------------------------------------  *
50;*  -------------------------------------------------  *
51;*  |  48 |  49 |  50 | 51  |           |           |  *
52;*  -------------------------------------------------  *
53;*  | 0xc0| 0xc4| 0xc8| 0xcc|           |           |  *
54;*  -------------------------------------------------  *
55;*  |     PC    |   align   |           |           |  *
56;*  -------------------------------------------------  *
57;*                                                     *
58;*******************************************************
59
60    AREA |.text|, CODE, READONLY, ALIGN=4, CODEALIGN
61    EXPORT make_fcontext
62    IMPORT _exit
63
64make_fcontext proc
65    ; save stack top address to x3
66    mov x3, x0
67
68    ; shift address in x0 (allocated stack) to lower 16 byte boundary
69    and x0, x0, ~0xF
70
71    ; reserve space for context-data on context-stack
72    sub  x0, x0, #0xd0
73
74    ; save top address of context_stack as 'base'
75    str  x3, [x0, #0xa0]
76    ; save bottom address of context-stack as 'limit' and 'dealloction stack'
77    sub  x3, x3, x1
78    stp  x3, x3, [x0, #0xa8]
79    ; save 0 as 'fiber data'
80    str  xzr, [x0, #0xb8]
81
82    ; third arg of make_fcontext() == address of context-function
83    ; store address as x19 for trampoline
84    str  x2, [x0, #0x40]
85    ; store trampoline address as pc
86    adr  x2, trampoline
87    str  x2, [x0, #0xc0]
88
89    ; save address of finish as return-address for context-function
90    ; will be entered after context-function returns (LR register)
91    adr  x1, finish
92    str  x1, [x0, #0x98]
93
94    ret  x30 ; return pointer to context-data (x0)
95
96trampoline
97    stp  fp, lr, [sp, #-0x10]!
98    mov  fp, sp
99    blr x19
100
101finish
102    ; exit code is zero
103    mov  x0, #0
104    ; exit application
105    bl  _exit
106    ENDP
107    END
108