libucontext/arch/common/common-trampoline.c

/*
 * Copyright (c) 2020 Ariadne Conill <ariadne@dereferenced.org>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * This software is provided 'as is' and without any warranty, express or
 * implied.  In no event shall the authors be liable for any damages arising
 * from the use of this software.
 */

#include <stddef.h>
#include <stdlib.h>
#include <stdio.h>

/* We need to make sure that the C compiler doesn't push any
 * additional data to the stack frame. Otherwise, assumptions
 * made by the architecture-specific implementation of the
 * FETCH_LINKPTR() macro about the location of the linkptr,
 * relative to the stack pointer, will not hold.
 *
 * Hence, we compile this function with -fomit-frame-pointer
 * and use the register storage-class specifier for all local
 * vars. Note that the latter is just a "suggestion" (see C99).
 */

__attribute__ ((visibility ("hidden")))
__attribute__ ((optimize ("omit-frame-pointer")))
void
libucontext_trampoline(void)
{
	register libucontext_ucontext_t *uc_link = NULL;

	FETCH_LINKPTR(uc_link);

	if (uc_link == NULL)
		exit(0);

	libucontext_setcontext(uc_link);
}