override.h

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/*
 * $Id: override.h,v 1.11 2006/02/02 05:35:31 cbiere Exp $
 *
 * Copyright (c) 2004, Raphael Manfredi
 *
 *----------------------------------------------------------------------
 * This file is part of gtk-gnutella.
 *
 *  gtk-gnutella is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  gtk-gnutella 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with gtk-gnutella; if not, write to the Free Software
 *  Foundation, Inc.:
 *      59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *----------------------------------------------------------------------
 */

#ifndef _override_h_
#define _override_h_

#ifdef FAST_ASSERTIONS
/*
 * The following variant should be faster than the usual g_assert() because
 * leaf functions stay leaf functions as it does not add function calls and the
 * generated code is smaller which allows better optimization. However, it
 * abuses deferencing a null pointer to cause a SIGSEGV or for x86 the "int
 * 0x03" assembler opcode to cause a SIGTRAP which is then caught by a signal
 * handler. This is provokes undefined behaviour and is not portable but
 * happens to work usually.
 *
 * Look at the generated code for functions which use assertion checks to see
 * the difference. It does not seem to make a significant difference in
 * performance overall though as it seems but that might be heavily
 * architecture-dependent.
 *
 * Taking advantage of it may require using -momit-leaf-frame-pointer or
 * -fomit-frame-pointer for GCC and an appropriate -march option is also
 * recommended.
 */
#undef g_assert
#undef g_assert_not_reached

static inline G_GNUC_NORETURN NON_NULL_PARAM((1)) void
eject_(const gchar *msg)
{
    extern const char *assert_msg_;

    assert_msg_ = msg;
    
#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
    {
        /* This should raise a SIGTRAP with minimum code */
        __asm__ __volatile__ ("int $03");
    }
#else
    {
        static volatile gint *assert_trigger_;
        *assert_trigger_ = 0;   /* ignite a SIGSEGV */
    }
#endif /* GCC/x86 */
}

#define g_assert(x)                                                           \
G_STMT_START {                                                                \
    if (G_UNLIKELY(!(x)))                                                     \
        eject_("\nAssertion failure \"" STRINGIFY(x) "\" in " G_STRLOC "\n"); \
} G_STMT_END

#define g_assert_not_reached()                                              \
    eject_("\nCode should not have been reached in " G_STRLOC "\n");        \

#endif /* FAST_ASSERTIONS */

#include "malloc.h"     /* Must be the last header included */

#endif /* _override_h_ */
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