1 | /* Create new context. |
2 | Copyright (C) 2015-2024 Free Software Foundation, Inc. |
3 | This file is part of the GNU C Library. |
4 | |
5 | The GNU C Library is free software; you can redistribute it and/or |
6 | modify it under the terms of the GNU Lesser General Public |
7 | License as published by the Free Software Foundation; either |
8 | version 2.1 of the License, or (at your option) any later version. |
9 | |
10 | The GNU C Library is distributed in the hope that it will be useful, |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
13 | Lesser General Public License for more details. |
14 | |
15 | You should have received a copy of the GNU Lesser General Public |
16 | License along with the GNU C Library; if not, see |
17 | <https://www.gnu.org/licenses/>. */ |
18 | |
19 | #include <sysdep.h> |
20 | #include <stdarg.h> |
21 | #include <stdint.h> |
22 | #include <ucontext.h> |
23 | |
24 | /* makecontext sets up a stack and the registers for the |
25 | user context. The stack looks like this: |
26 | |
27 | +-----------------------+ |
28 | | padding as required | |
29 | +-----------------------+ |
30 | sp -> | parameters 5 to n | |
31 | +-----------------------+ |
32 | |
33 | The registers are set up like this: |
34 | r4--r7 : parameter 1 to 4 |
35 | r16 : uc_link |
36 | sp : stack pointer. |
37 | */ |
38 | |
39 | void |
40 | __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...) |
41 | { |
42 | extern void __startcontext (void); |
43 | unsigned long *sp; |
44 | va_list ap; |
45 | int i; |
46 | |
47 | sp = (unsigned long *) |
48 | ((uintptr_t) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size); |
49 | |
50 | /* Allocate stack arguments. */ |
51 | sp -= argc < 4 ? 0 : argc - 4; |
52 | |
53 | /* Keep the stack aligned. */ |
54 | sp = (unsigned long*) (((uintptr_t) sp) & -4L); |
55 | |
56 | /* Init version field. */ |
57 | ucp->uc_mcontext.version = 2; |
58 | /* Keep uc_link in r16. */ |
59 | ucp->uc_mcontext.regs[15] = (uintptr_t) ucp->uc_link; |
60 | /* Return address points to __startcontext(). */ |
61 | ucp->uc_mcontext.regs[23] = (uintptr_t) &__startcontext; |
62 | /* Frame pointer is null. */ |
63 | ucp->uc_mcontext.regs[24] = (uintptr_t) 0; |
64 | /* Restart in user-space starting at 'func'. */ |
65 | ucp->uc_mcontext.regs[27] = (uintptr_t) func; |
66 | /* Set stack pointer. */ |
67 | ucp->uc_mcontext.regs[28] = (uintptr_t) sp; |
68 | |
69 | va_start (ap, argc); |
70 | for (i = 0; i < argc; ++i) |
71 | if (i < 4) |
72 | ucp->uc_mcontext.regs[i + 3] = va_arg (ap, unsigned long); |
73 | else |
74 | sp[i - 4] = va_arg (ap, unsigned long); |
75 | |
76 | va_end (ap); |
77 | } |
78 | |
79 | weak_alias (__makecontext, makecontext) |
80 | |