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1;/*
2;            Copyright Oliver Kowalke 2009.
3;   Distributed under the Boost Software License, Version 1.0.
4;      (See accompanying file LICENSE_1_0.txt or copy at
5;          http://www.boost.org/LICENSE_1_0.txt)
6;*/
7
8; *******************************************************
9; *                                                     *
10; *  -------------------------------------------------  *
11; *  |  0  |  1  |  2  |  3  |  4  |  5  |  6  |  7  |  *
12; *  -------------------------------------------------  *
13; *  | 0x0 | 0x4 | 0x8 | 0xc | 0x10| 0x14| 0x18| 0x1c|  *
14; *  -------------------------------------------------  *
15; *  |deall|limit| base|hiddn|  v1 |  v2 |  v3 |  v4 |  *
16; *  -------------------------------------------------  *
17; *  -------------------------------------------------  *
18; *  |  8  |  9  |  10 |  11 |  12 |  13 |  14 |  15 |  *
19; *  -------------------------------------------------  *
20; *  | 0x20| 0x24| 0x28| 0x2c| 0x30| 0x34| 0x38| 0x3c|  *
21; *  -------------------------------------------------  *
22; *  |  v5 |  v6 |  v7 |  v8 |  lr |  pc | FCTX| DATA|  *
23; *  -------------------------------------------------  *
24; *                                                     *
25; *******************************************************
26
27    AREA |.text|, CODE
28    ALIGN 4
29    EXPORT ontop_fcontext
30
31ontop_fcontext PROC
32    ; save LR as PC
33    push {lr}
34    ; save hidden,V1-V8,LR
35    push {a1,v1-v8,lr}
36
37    ; load TIB to save/restore thread size and limit.
38    ; we do not need preserve CPU flag and can use it's arg register
39    mrc     p15, #0, v1, c13, c0, #2
40
41    ; save current stack base
42    ldr  a1, [v1, #0x04]
43    push {a1}
44    ; save current stack limit
45    ldr  a1, [v1, #0x08]
46    push {a1}
47    ; save current deallocation stack
48    ldr  a1, [v1, #0xe0c]
49    push {a1}
50
51    ; store RSP (pointing to context-data) in A1
52    mov  a1, sp
53
54    ; restore RSP (pointing to context-data) from A2
55    mov  sp, a2
56
57    ; restore stack base
58    pop  {a1}
59    str  a1, [v1, #0x04]
60    ; restore stack limit
61    pop  {a1}
62    str  a1, [v1, #0x08]
63    ; restore deallocation stack
64    pop  {a1}
65    str  a1, [v1, #0xe0c]
66
67    ; store parent context in A2
68    mov  a2, a1
69
70    ; restore hidden,V1-V8,LR
71    pop {a1,v1-v8,lr}
72
73    ; return transfer_t from jump
74    str  a2, [a1, #0]
75    str  a3, [a1, #4]
76    ; pass transfer_t as first arg in context function
77    ; A1 == hidden, A2 == FCTX, A3 == DATA
78
79    ; skip PC
80    add  sp, sp, #4
81
82    ; jump to ontop-function
83    bx  a4
84
85    ENDP
86    END
87