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

   1 /* Copyright (C) 2001 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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <libintl.h>
  21 #include <stdarg.h>
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <ucontext.h>
  25
  26 /* This implementation can handle any ARGC value but only
  27    normal integer type parameters. Parameters of type float,
  28    double, complex and structure with sizes 0, 2, 4 or 8
  29    won't work.
  30    makecontext sets up a stack and the registers for the
  31    user context. The stack looks like this:
  32            size                         offset
  33     %r15 ->    +-----------------------+
  34              8 | back chain (zero)     |  0
  35              8 | reserved              |  8
  36            144 | save area for (*func) | 16
  37                +-----------------------+
  38              n | overflow parameters   | 160
  39                +-----------------------+
  40              8 | trampoline            | 160+n
  41                +-----------------------+
  42    The registers are set up like this:
  43      %r2-%r6: parameters 1 to 5
  44      %r7    : (*func) pointer
  45      %r8    : uc_link from ucontext structure
  46      %r9    : address of setcontext
  47      %r14   : return address to uc_link trampoline
  48      %r15   : stack pointer.
  49
  50    The trampoline looks like this:
  51      basr  %r14,%r7
  52      lgr   %r2,%r8
  53      br    %r9.  */
  54
  55 void
  56 __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
  57 {
  58   unsigned long *sp;
  59   va_list ap;
  60   int i;
  61
  62   sp = (long *) (((long) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size) & -8L);
  63
  64   /* Setup the trampoline.  */
  65   *--sp = 0x0de7b904002807f9;
  66
  67   /* Set the return address to trampoline.  */
  68   ucp->uc_mcontext.gregs[14] = (long) sp;
  69
  70   /* Set register parameters.  */
  71   va_start (ap, argc);
  72   for (i = 0; (i < argc) && (i < 5); i++)
  73     ucp->uc_mcontext.gregs[2+i] = va_arg (ap, long);
  74
  75   /* The remaining arguments go to the overflow area.  */
  76   if (argc > 5) {
  77     sp -= argc - 5;
  78     for (i = 5; i < argc; i++)
  79       sp[i] = va_arg(ap, long);
  80   }
  81   va_end (ap);
  82
  83   /* Make room for the save area and set the backchain.  */
  84   sp -= 20;
  85   *sp = 0;
  86
  87   /* Pass (*func) to __start_context in %r7.  */
  88   ucp->uc_mcontext.gregs[7] = (long) func;
  89
  90   /* Pass ucp->uc_link to __start_context in %r8.  */
  91   ucp->uc_mcontext.gregs[8] = (long) ucp->uc_link;
  92
  93   /* Pass address of setcontext in %r9.  */
  94   ucp->uc_mcontext.gregs[9] = (long) &setcontext;
  95
  96   /* Set stack pointer.  */
  97   ucp->uc_mcontext.gregs[15] = (long) sp;
  98 }
  99
 100 weak_alias (__makecontext, makecontext)