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/* Create new context.
Copyright (C) 2015-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
#include <stdarg.h>
#include <stdint.h>
#include <ucontext.h>
/* makecontext sets up a stack and the registers for the
user context. The stack looks like this:
+-----------------------+
| padding as required |
+-----------------------+
sp -> | parameters 5 to n |
+-----------------------+
The registers are set up like this:
r4--r7 : parameter 1 to 4
r16 : uc_link
sp : stack pointer.
*/
void
__makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
{
extern void __startcontext (void);
unsigned long *sp;
va_list ap;
int i;
sp = (unsigned long *)
((uintptr_t) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
/* Allocate stack arguments. */
sp -= argc < 4 ? 0 : argc - 4;
/* Keep the stack aligned. */
sp = (unsigned long*) (((uintptr_t) sp) & -4L);
/* Init version field. */
ucp->uc_mcontext.version = 2;
/* Keep uc_link in r16. */
ucp->uc_mcontext.regs[15] = (uintptr_t) ucp->uc_link;
/* Return address points to __startcontext(). */
ucp->uc_mcontext.regs[23] = (uintptr_t) &__startcontext;
/* Frame pointer is null. */
ucp->uc_mcontext.regs[24] = (uintptr_t) 0;
/* Restart in user-space starting at 'func'. */
ucp->uc_mcontext.regs[27] = (uintptr_t) func;
/* Set stack pointer. */
ucp->uc_mcontext.regs[28] = (uintptr_t) sp;
va_start (ap, argc);
for (i = 0; i < argc; ++i)
if (i < 4)
ucp->uc_mcontext.regs[i + 3] = va_arg (ap, unsigned long);
else
sp[i - 4] = va_arg (ap, unsigned long);
va_end (ap);
}
weak_alias (__makecontext, makecontext)
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