1  /* Create new context.
       2     Copyright (C) 2008-2023 Free Software Foundation, Inc.
       3     This file is part of the GNU C Library.
       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     <https://www.gnu.org/licenses/>.  */
      18  
      19  #include <sysdep.h>
      20  #include <stdarg.h>
      21  #include <stdint.h>
      22  #include <ucontext.h>
      23  
      24  /* Sets up the outgoing arguments and the program counter for a user
      25     context for the requested function call.
      26  
      27     Returning to the correct parent context is pretty simple on
      28     Sparc.  We only need to link up the register windows correctly.
      29     Since global registers are clobbered by calls, we need not be
      30     concerned about those, and thus is all could be worked out without
      31     using a trampoline.
      32  
      33     Except that we must deal with the signal mask, thus a trampoline
      34     is unavoidable. 32-bit stackframe layout:
      35  	      +-----------------------------------------+
      36  	      | 7th and further parameters		|
      37  	      +-----------------------------------------+
      38  	      | backup storage for initial 6 parameters |
      39  	      +-----------------------------------------+
      40  	      | struct return pointer			|
      41  	      +-----------------------------------------+
      42  	      | 8 incoming registers			|
      43  	      +-----------------------------------------+
      44  	      | 8 local registers			|
      45       %sp -->  +-----------------------------------------+
      46  
      47  */
      48  
      49  void
      50  __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
      51  {
      52    extern void __start_context (void);
      53    unsigned long int *sp;
      54    va_list ap;
      55    int i;
      56  
      57    sp = (unsigned long int *) (ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
      58    sp -= 16 + 7 + argc;
      59    sp = (unsigned long int *) (((uintptr_t) sp) & ~(8 - 1));
      60  
      61    for (i = 0; i < 8; i++)
      62      sp[i + 8] = ucp->uc_mcontext.gregs[REG_O0 + i];
      63  
      64    /* The struct return pointer is essentially unused, so we can
      65       place the link there.  */
      66    sp[16] = (unsigned long int) ucp->uc_link;
      67  
      68    va_start (ap, argc);
      69  
      70    /* Fill in outgoing arguments, including those which will
      71       end up being passed on the stack.  */
      72    for (i = 0; i < argc; i++)
      73      {
      74        unsigned long int arg = va_arg (ap, unsigned long int);
      75        if (i < 6)
      76  	ucp->uc_mcontext.gregs[REG_O0 + i] = arg;
      77        else
      78  	sp[i + 23 - 6] = arg;
      79      }
      80  
      81    va_end (ap);
      82  
      83    ucp->uc_mcontext.gregs[REG_O6] = (unsigned long int) sp;
      84  
      85    ucp->uc_mcontext.gregs[REG_O7] = ((unsigned long int) __start_context) - 8;
      86  
      87    ucp->uc_mcontext.gregs[REG_PC] = (unsigned long int) func;
      88    ucp->uc_mcontext.gregs[REG_nPC] = ucp->uc_mcontext.gregs[REG_PC] + 4;
      89  }
      90  
      91  weak_alias (__makecontext, makecontext)