1/* Create new context.
2 Copyright (C) 2002-2016 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Andreas Jaeger <aj@suse.de>, 2002.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <http://www.gnu.org/licenses/>. */
19
20#include <sysdep.h>
21#include <stdarg.h>
22#include <stdint.h>
23#include <ucontext.h>
24
25#include "ucontext_i.h"
26
27/* This implementation can handle any ARGC value but only
28 normal integer parameters.
29 makecontext sets up a stack and the registers for the
30 user context. The stack looks like this:
31 +-----------------------+
32 | next context |
33 +-----------------------+
34 | parameter 7-n |
35 +-----------------------+
36 | trampoline address |
37 %rsp -> +-----------------------+
38
39 The registers are set up like this:
40 %rdi,%rsi,%rdx,%rcx,%r8,%r9: parameter 1 to 6
41 %rbx : address of next context
42 %rsp : stack pointer.
43*/
44
45/* XXX: This implementation currently only handles integer arguments.
46 To handle long int and pointer arguments the va_arg arguments needs
47 to be changed to long and also the stdlib/tst-setcontext.c file needs
48 to be changed to pass long arguments to makecontext. */
49
50
51void
52__makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
53{
54 extern void __start_context (void);
55 greg_t *sp;
56 unsigned int idx_uc_link;
57 va_list ap;
58 int i;
59
60 /* Generate room on stack for parameter if needed and uc_link. */
61 sp = (greg_t *) ((uintptr_t) ucp->uc_stack.ss_sp
62 + ucp->uc_stack.ss_size);
63 sp -= (argc > 6 ? argc - 6 : 0) + 1;
64 /* Align stack and make space for trampoline address. */
65 sp = (greg_t *) ((((uintptr_t) sp) & -16L) - 8);
66
67 idx_uc_link = (argc > 6 ? argc - 6 : 0) + 1;
68
69 /* Setup context ucp. */
70 /* Address to jump to. */
71 ucp->uc_mcontext.gregs[REG_RIP] = (uintptr_t) func;
72 /* Setup rbx.*/
73 ucp->uc_mcontext.gregs[REG_RBX] = (uintptr_t) &sp[idx_uc_link];
74 ucp->uc_mcontext.gregs[REG_RSP] = (uintptr_t) sp;
75
76 /* Setup stack. */
77 sp[0] = (uintptr_t) &__start_context;
78 sp[idx_uc_link] = (uintptr_t) ucp->uc_link;
79
80 va_start (ap, argc);
81 /* Handle arguments.
82
83 The standard says the parameters must all be int values. This is
84 an historic accident and would be done differently today. For
85 x86-64 all integer values are passed as 64-bit values and
86 therefore extending the API to copy 64-bit values instead of
87 32-bit ints makes sense. It does not break existing
88 functionality and it does not violate the standard which says
89 that passing non-int values means undefined behavior. */
90 for (i = 0; i < argc; ++i)
91 switch (i)
92 {
93 case 0:
94 ucp->uc_mcontext.gregs[REG_RDI] = va_arg (ap, greg_t);
95 break;
96 case 1:
97 ucp->uc_mcontext.gregs[REG_RSI] = va_arg (ap, greg_t);
98 break;
99 case 2:
100 ucp->uc_mcontext.gregs[REG_RDX] = va_arg (ap, greg_t);
101 break;
102 case 3:
103 ucp->uc_mcontext.gregs[REG_RCX] = va_arg (ap, greg_t);
104 break;
105 case 4:
106 ucp->uc_mcontext.gregs[REG_R8] = va_arg (ap, greg_t);
107 break;
108 case 5:
109 ucp->uc_mcontext.gregs[REG_R9] = va_arg (ap, greg_t);
110 break;
111 default:
112 /* Put value on stack. */
113 sp[i - 5] = va_arg (ap, greg_t);
114 break;
115 }
116 va_end (ap);
117
118}
119
120
121weak_alias (__makecontext, makecontext)
122