sysdeps/unix/sysv/linux/x86_64/makecontext.c

   1 /* Create new context.
   2    Copyright (C) 2002, 2004, 2005, 2008 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Andreas Jaeger <aj@suse.de>, 2002.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #include <sysdep.h>
  22 #include <stdarg.h>
  23 #include <stdint.h>
  24 #include <ucontext.h>
  25
  26 #include "ucontext_i.h"
  27
  28 /* This implementation can handle any ARGC value but only
  29    normal integer parameters.
  30    makecontext sets up a stack and the registers for the
  31    user context. The stack looks like this:
  32                +-----------------------+
  33                | next context          |
  34                +-----------------------+
  35                | parameter 7-n         |
  36                +-----------------------+
  37                | trampoline address    |
  38     %rsp ->    +-----------------------+
  39
  40    The registers are set up like this:
  41      %rdi,%rsi,%rdx,%rcx,%r8,%r9: parameter 1 to 6
  42      %rbx   : address of next context
  43      %rsp   : stack pointer.
  44 */
  45
  46 /* XXX: This implementation currently only handles integer arguments.
  47    To handle long int and pointer arguments the va_arg arguments needs
  48    to be changed to long and also the stdlib/tst-setcontext.c file needs
  49    to be changed to pass long arguments to makecontext.  */
  50
  51
  52 void
  53 __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
  54 {
  55   extern void __start_context (void);
  56   unsigned long int *sp, idx_uc_link;
  57   va_list ap;
  58   int i;
  59
  60   /* Generate room on stack for parameter if needed and uc_link.  */
  61   sp = (unsigned long int *) ((uintptr_t) ucp->uc_stack.ss_sp
  62                               + ucp->uc_stack.ss_size);
  63   sp -= (argc > 6 ? argc - 6 : 0) + 1;
  64   /* Align stack and make space for trampoline address.  */
  65   sp = (unsigned long int *) ((((uintptr_t) sp) & -16L) - 8);
  66
  67   idx_uc_link = (argc > 6 ? argc - 6 : 0) + 1;
  68
  69   /* Setup context ucp.  */
  70   /* Address to jump to.  */
  71   ucp->uc_mcontext.gregs[REG_RIP] = (long int) func;
  72   /* Setup rbx.*/
  73   ucp->uc_mcontext.gregs[REG_RBX] = (long int) &sp[idx_uc_link];
  74   ucp->uc_mcontext.gregs[REG_RSP] = (long int) sp;
  75
  76   /* Setup stack.  */
  77   sp[0] = (unsigned long int) &__start_context;
  78   sp[idx_uc_link] = (unsigned long int) ucp->uc_link;
  79
  80   va_start (ap, argc);
  81   /* Handle arguments.
  82
  83      The standard says the parameters must all be int values.  This is
  84      an historic accident and would be done differently today.  For
  85      x86-64 all integer values are passed as 64-bit values and
  86      therefore extending the API to copy 64-bit values instead of
  87      32-bit ints makes sense.  It does not break existing
  88      functionality and it does not violate the standard which says
  89      that passing non-int values means undefined behavior.  */
  90   for (i = 0; i < argc; ++i)
  91     switch (i)
  92       {
  93       case 0:
  94         ucp->uc_mcontext.gregs[REG_RDI] = va_arg (ap, long int);
  95         break;
  96       case 1:
  97         ucp->uc_mcontext.gregs[REG_RSI] = va_arg (ap, long int);
  98         break;
  99       case 2:
 100         ucp->uc_mcontext.gregs[REG_RDX] = va_arg (ap, long int);
 101         break;
 102       case 3:
 103         ucp->uc_mcontext.gregs[REG_RCX] = va_arg (ap, long int);
 104         break;
 105       case 4:
 106         ucp->uc_mcontext.gregs[REG_R8] = va_arg (ap, long int);
 107         break;
 108       case 5:
 109         ucp->uc_mcontext.gregs[REG_R9] = va_arg (ap, long int);
 110         break;
 111       default:
 112         /* Put value on stack.  */
 113         sp[i - 5] = va_arg (ap, unsigned long int);
 114         break;
 115       }
 116   va_end (ap);
 117
 118 }
 119
 120
 121 weak_alias (__makecontext, makecontext)