sysdeps/unix/sysv/linux/s390/s390-32/makecontext.c

   1 /* Copyright (C) 2001-2023 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    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <libintl.h>
  19 #include <stdarg.h>
  20 #include <stdio.h>
  21 #include <stdlib.h>
  22 #include <ucontext.h>
  23
  24 /* This implementation can handle any ARGC value but only
  25    normal integer type parameters. Parameters of type float,
  26    double, complex and structure with sizes 0, 2, 4 or 8
  27    won't work.
  28    makecontext sets up a stack and the registers for the
  29    user context. The stack looks like this:
  30            size                         offset
  31     %r15 ->    +-----------------------+
  32              4 | back chain (zero)     |  0
  33              4 | reserved              |  4
  34             88 | save area for (*func) |  8
  35                +-----------------------+
  36              n | overflow parameters   | 96
  37                +-----------------------+
  38    The registers are set up like this:
  39      %r2-%r6: parameters 1 to 5
  40      %r7    : (*func) pointer
  41      %r8    : uc_link from ucontext structure
  42      %r9    : address of setcontext
  43      %r14   : return address to uc_link trampoline
  44      %r15   : stack pointer.
  45
  46    The trampoline looks like this:
  47      basr  %r14,%r7
  48      lr    %r2,%r8
  49      br    %r9.  */
  50
  51 void
  52 __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
  53 {
  54   extern void __makecontext_ret (void);
  55   unsigned long int *sp;
  56   va_list ap;
  57
  58   sp = (unsigned long int *) (((unsigned long int) ucp->uc_stack.ss_sp
  59                                + ucp->uc_stack.ss_size) & -8L);
  60
  61   /* Set the return address to trampoline.  */
  62   ucp->uc_mcontext.gregs[14] = (long int) __makecontext_ret;
  63
  64   /* Set register parameters.  */
  65   va_start (ap, argc);
  66   for (int i = 0; i < argc && i < 5; ++i)
  67     ucp->uc_mcontext.gregs[2 + i] = va_arg (ap, long int);
  68
  69   /* The remaining arguments go to the overflow area.  */
  70   if (argc > 5)
  71     {
  72       sp -= argc - 5;
  73       for (int i = 5; i < argc; ++i)
  74         sp[i - 5] = va_arg (ap, long int);
  75     }
  76   va_end (ap);
  77
  78   /* Make room for the save area and set the backchain.  */
  79   sp -= 24;
  80   *sp = 0;
  81
  82   /* Pass (*func) to __makecontext_ret in %r7.  */
  83   ucp->uc_mcontext.gregs[7] = (long int) func;
  84
  85   /* Pass ucp->uc_link to __makecontext_ret in %r8.  */
  86   ucp->uc_mcontext.gregs[8] = (long int) ucp->uc_link;
  87
  88   /* Pass address of setcontext in %r9.  */
  89   ucp->uc_mcontext.gregs[9] = (long int) &setcontext;
  90
  91   /* Set stack pointer.  */
  92   ucp->uc_mcontext.gregs[15] = (long int) sp;
  93 }
  94
  95 weak_alias (__makecontext, makecontext)