/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2004 Suleiman Souhlal
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/param.h>

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

__weak_reference(__makecontext, makecontext);

void _ctx_done(ucontext_t *ucp);
void _ctx_start(void);

void
_ctx_done(ucontext_t *ucp)
{
        if (ucp->uc_link == NULL)
                exit(0);
        else {
                /* invalidate context */
                ucp->uc_mcontext.mc_len = 0;

                setcontext((const ucontext_t *)ucp->uc_link);

                abort(); /* should never return from above call */
        }
}

void
__makecontext(ucontext_t *ucp, void (*start)(void), int argc, ...)
{
        mcontext_t *mc;
        char *sp;
        va_list ap;
        int i, regargs, stackargs;

        /* Sanity checks */
        if ((ucp == NULL) || (argc < 0)
            || (ucp->uc_stack.ss_sp == NULL)
            || (ucp->uc_stack.ss_size < MINSIGSTKSZ)) {
                /* invalidate context */
                ucp->uc_mcontext.mc_len = 0;
                return;
        }

        /*
         * The stack must have space for the frame pointer, saved
         * link register, overflow arguments, and be 16-byte
         * aligned.
         */
        stackargs = (argc > 8) ? argc - 8 : 0;
        sp = (char *) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size
                - sizeof(uint32_t)*(stackargs + 2);
        sp = (char *)((uint32_t)sp & ~0x1f);

        mc = &ucp->uc_mcontext;

        /*
         * Up to 8 register args. Assumes all args are 32-bit and
         * integer only. Not sure how to cater for floating point,
         * although 64-bit args will work if aligned correctly
         * in the arg list.
         */
        regargs = (argc > 8) ? 8 : argc;
        va_start(ap, argc);
        for (i = 0; i < regargs; i++)
                mc->mc_gpr[3 + i] = va_arg(ap, uint32_t);

        /*
         * Overflow args go onto the stack
         */
        if (argc > 8) {
                uint32_t *argp;

                /* Skip past frame pointer and saved LR */
                argp = (uint32_t *)sp + 2;

                for (i = 0; i < stackargs; i++)
                        *argp++ = va_arg(ap, uint32_t);
        }
        va_end(ap);

        /*
         * Use caller-saved regs 14/15 to hold params that _ctx_start
         * will use to invoke the user-supplied func
         */
        mc->mc_srr0 = (uint32_t) _ctx_start;
        mc->mc_gpr[1] = (uint32_t) sp;          /* new stack pointer */
        mc->mc_gpr[14] = (uint32_t) start;      /* r14 <- start */
        mc->mc_gpr[15] = (uint32_t) ucp;        /* r15 <- ucp */
}