1/* Create new context.
2 Copyright (C) 2008-2022 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/* Sets up the outgoing arguments and the program counter for a user
25 context for the requested function call.
26
27 Returning to the correct parent context is pretty simple on
28 Sparc. We only need to link up the register windows correctly.
29 Since global registers are clobbered by calls, we need not be
30 concerned about those, and thus is all could be worked out without
31 using a trampoline.
32
33 Except that we must deal with the signal mask, thus a trampoline
34 is unavoidable. 32-bit stackframe layout:
35 +-----------------------------------------+
36 | 7th and further parameters |
37 +-----------------------------------------+
38 | backup storage for initial 6 parameters |
39 +-----------------------------------------+
40 | struct return pointer |
41 +-----------------------------------------+
42 | 8 incoming registers |
43 +-----------------------------------------+
44 | 8 local registers |
45 %sp --> +-----------------------------------------+
46
47*/
48
49void
50__makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
51{
52 extern void __start_context (void);
53 unsigned long int *sp;
54 va_list ap;
55 int i;
56
57 sp = (unsigned long int *) (ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
58 sp -= 16 + 7 + argc;
59 sp = (unsigned long int *) (((uintptr_t) sp) & ~(8 - 1));
60
61 for (i = 0; i < 8; i++)
62 sp[i + 8] = ucp->uc_mcontext.gregs[REG_O0 + i];
63
64 /* The struct return pointer is essentially unused, so we can
65 place the link there. */
66 sp[16] = (unsigned long int) ucp->uc_link;
67
68 va_start (ap, argc);
69
70 /* Fill in outgoing arguments, including those which will
71 end up being passed on the stack. */
72 for (i = 0; i < argc; i++)
73 {
74 unsigned long int arg = va_arg (ap, unsigned long int);
75 if (i < 6)
76 ucp->uc_mcontext.gregs[REG_O0 + i] = arg;
77 else
78 sp[i + 23 - 6] = arg;
79 }
80
81 va_end (ap);
82
83 ucp->uc_mcontext.gregs[REG_O6] = (unsigned long int) sp;
84
85 ucp->uc_mcontext.gregs[REG_O7] = ((unsigned long int) __start_context) - 8;
86
87 ucp->uc_mcontext.gregs[REG_PC] = (unsigned long int) func;
88 ucp->uc_mcontext.gregs[REG_nPC] = ucp->uc_mcontext.gregs[REG_PC] + 4;
89}
90
91weak_alias (__makecontext, makecontext)
92

source code of glibc/sysdeps/unix/sysv/linux/sparc/sparc32/makecontext.c