/* Copyright (C) 2001-2024 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <libintl.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <ucontext.h>

/* This implementation can handle any ARGC value but only
   normal integer type parameters. Parameters of type float,
   double, complex and structure with sizes 0, 2, 4 or 8
   won't work.
   makecontext sets up a stack and the registers for the
   user context. The stack looks like this:
	   size                         offset
    %r15 ->    +-----------------------+
	     4 | back chain (zero)     |  0
	     4 | reserved              |  4
	    88 | save area for (*func) |  8
	       +-----------------------+
	     n | overflow parameters   | 96
	       +-----------------------+
   The registers are set up like this:
     %r2-%r6: parameters 1 to 5
     %r7    : (*func) pointer
     %r8    : uc_link from ucontext structure
     %r9    : address of setcontext
     %r14   : return address to uc_link trampoline
     %r15   : stack pointer.

   The trampoline looks like this:
     basr  %r14,%r7
     lr    %r2,%r8
     br    %r9.  */

void
__makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
{
  extern void __makecontext_ret (void);
  unsigned long int *sp;
  va_list ap;

  sp = (unsigned long int *) (((unsigned long int) ucp->uc_stack.ss_sp
			       + ucp->uc_stack.ss_size) & -8L);

  /* Set the return address to trampoline.  */
  ucp->uc_mcontext.gregs[14] = (long int) __makecontext_ret;
  /* Store psw mask to 0x0 and addr to trampoline.  Then the address
     can be retrieved from the ucontext structure in the same way as if it
     is created by kernel and passed to a signal-handler.  */
  ucp->uc_mcontext.psw.addr = (long int) __makecontext_ret;
  ucp->uc_mcontext.psw.mask = 0;

  /* Set register parameters.  */
  va_start (ap, argc);
  for (int i = 0; i < argc && i < 5; ++i)
    ucp->uc_mcontext.gregs[2 + i] = va_arg (ap, long int);

  /* The remaining arguments go to the overflow area.  */
  if (argc > 5)
    {
      sp -= argc - 5;
      for (int i = 5; i < argc; ++i)
	sp[i - 5] = va_arg (ap, long int);
    }
  va_end (ap);

  /* Make room for the save area and set the backchain.  */
  sp -= 24;
  *sp = 0;

  /* Pass (*func) to __makecontext_ret in %r7.  */
  ucp->uc_mcontext.gregs[7] = (long int) func;

  /* Pass ucp->uc_link to __makecontext_ret in %r8.  */
  ucp->uc_mcontext.gregs[8] = (long int) ucp->uc_link;

  /* Pass address of setcontext in %r9.  */
  ucp->uc_mcontext.gregs[9] = (long int) &setcontext;

  /* Set stack pointer.  */
  ucp->uc_mcontext.gregs[15] = (long int) sp;
}

weak_alias (__makecontext, makecontext)