sysdeps/unix/sysv/linux/s390/s390-64/makecontext.c

   1 /* Copyright (C) 2001-2014 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Martin Schwidefsky (schwidefsky@de.ibm.com).
   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 <libintl.h>
  20 #include <stdarg.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <ucontext.h>
  24
  25 /* This implementation can handle any ARGC value but only
  26    normal integer type parameters. Parameters of type float,
  27    double, complex and structure with sizes 0, 2, 4 or 8
  28    won't work.
  29    makecontext sets up a stack and the registers for the
  30    user context. The stack looks like this:
  31            size                         offset
  32     %r15 ->    +-----------------------+
  33              8 | back chain (zero)     |  0
  34              8 | reserved              |  8
  35            144 | save area for (*func) | 16
  36                +-----------------------+
  37              n | overflow parameters   | 160
  38                +-----------------------+
  39    The registers are set up like this:
  40      %r2-%r6: parameters 1 to 5
  41      %r7    : (*func) pointer
  42      %r8    : uc_link from ucontext structure
  43      %r9    : address of setcontext
  44      %r14   : return address to uc_link trampoline
  45      %r15   : stack pointer.
  46
  47    The trampoline looks like this:
  48      basr  %r14,%r7
  49      lgr   %r2,%r8
  50      br    %r9.  */
  51
  52 void
  53 __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
  54 {
  55   extern void __makecontext_ret (void);
  56   unsigned long int *sp;
  57   va_list ap;
  58
  59   sp = (unsigned long int *) (((unsigned long int) ucp->uc_stack.ss_sp
  60                                + ucp->uc_stack.ss_size) & -8L);
  61
  62   /* Set the return address to trampoline.  */
  63   ucp->uc_mcontext.gregs[14] = (long int) __makecontext_ret;
  64
  65   /* Set register parameters.  */
  66   va_start (ap, argc);
  67   for (int i = 0; i < argc && i < 5; ++i)
  68     ucp->uc_mcontext.gregs[2 + i] = va_arg (ap, long int);
  69
  70   /* The remaining arguments go to the overflow area.  */
  71   if (argc > 5)
  72     {
  73       sp -= argc - 5;
  74       for (int i = 5; i < argc; ++i)
  75         sp[i - 5] = va_arg (ap, long int);
  76     }
  77   va_end (ap);
  78
  79   /* Make room for the save area and set the backchain.  */
  80   sp -= 20;
  81   *sp = 0;
  82
  83   /* Pass (*func) to __makecontext_ret in %r7.  */
  84   ucp->uc_mcontext.gregs[7] = (long int) func;
  85
  86   /* Pass ucp->uc_link to __makecontext_ret in %r8.  */
  87   ucp->uc_mcontext.gregs[8] = (long int) ucp->uc_link;
  88
  89   /* Pass address of setcontext in %r9.  */
  90   ucp->uc_mcontext.gregs[9] = (long int) &setcontext;
  91
  92   /* Set stack pointer.  */
  93   ucp->uc_mcontext.gregs[15] = (long int) sp;
  94 }
  95
  96 weak_alias (__makecontext, makecontext)