sysdeps/unix/sysv/linux/nios2/makecontext.c

   1 /* Create new context.
   2    Copyright (C) 2015-2019 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    <http://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)