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

   1 /* Copyright (C) 2012 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <stdarg.h>
  19 #include <ucontext.h>
  20
  21 /* Number of arguments that go in registers.  */
  22 #define NREG_ARGS  4
  23
  24 /* Take a context previously prepared via getcontext() and set to
  25    call func() with the given int only args.  */
  26 void
  27 __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
  28 {
  29   extern void __startcontext (void);
  30   unsigned long *funcstack;
  31   va_list vl;
  32   unsigned long *regptr;
  33   unsigned int reg;
  34   int misaligned;
  35
  36   /* Start at the top of stack.  */
  37   funcstack = (unsigned long *) (ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
  38
  39   /* Ensure the stack stays eight byte aligned.  */
  40   misaligned = ((unsigned long) funcstack & 4) != 0;
  41
  42   if ((argc > NREG_ARGS) && (argc & 1) != 0)
  43     misaligned = !misaligned;
  44
  45   if (misaligned)
  46     funcstack -= 1;
  47
  48   va_start (vl, argc);
  49
  50   /* Reserve space for the on-stack arguments.  */
  51   if (argc > NREG_ARGS)
  52     funcstack -= (argc - NREG_ARGS);
  53
  54   ucp->uc_mcontext.arm_sp = (unsigned long) funcstack;
  55   ucp->uc_mcontext.arm_pc = (unsigned long) func;
  56
  57   /* Exit to startcontext() with the next context in R4 */
  58   ucp->uc_mcontext.arm_r4 = (unsigned long) ucp->uc_link;
  59   ucp->uc_mcontext.arm_lr = (unsigned long) __startcontext;
  60
  61   /* The first four arguments go into registers.  */
  62   regptr = &(ucp->uc_mcontext.arm_r0);
  63
  64   for (reg = 0; (reg < argc) && (reg < NREG_ARGS); reg++)
  65     *regptr++ = va_arg (vl, unsigned long);
  66
  67   /* And the remainder on the stack.  */
  68   for (; reg < argc; reg++)
  69     *funcstack++ = va_arg (vl, unsigned long);
  70
  71   va_end (vl);
  72 }
  73 weak_alias (__makecontext, makecontext)