freebsd.h

gcc-you can use this code to learn something about gcc, and inquire further into linux,

/* Definitions for Intel 386 running FreeBSD with ELF format
   Copyright (C) 1996, 2000, 2002 Free Software Foundation, Inc.
   Contributed by Eric Youngdale.
   Modified for stabs-in-ELF by H.J. Lu.
   Adapted from GNU/Linux version by John Polstra.
   Continued development by David O'Brien <[e-mail]>

This file is part of GNU CC.

GNU CC 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, or (at your option)
any later version.

GNU CC 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 GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */


#define TARGET_VERSION fprintf (stderr, " (i386 FreeBSD/ELF)");

/* Override the default comment-starter of "/".  */
#undef  ASM_COMMENT_START
#define ASM_COMMENT_START "#"

#undef  ASM_APP_ON
#define ASM_APP_ON "#APP\n"

#undef  ASM_APP_OFF
#define ASM_APP_OFF "#NO_APP\n"

#undef  DBX_REGISTER_NUMBER
#define DBX_REGISTER_NUMBER(n) \
  (TARGET_64BIT ? dbx64_register_map[n] : svr4_dbx_register_map[n])

#undef  NO_PROFILE_COUNTERS
#define NO_PROFILE_COUNTERS

/* Tell final.c that we don't need a label passed to mcount.  */

#undef  MCOUNT_NAME
#define MCOUNT_NAME ".mcount"

/* Make gcc agree with <machine/ansi.h>.  */

#undef  SIZE_TYPE
#define SIZE_TYPE "unsigned int"
 
#undef  PTRDIFF_TYPE
#define PTRDIFF_TYPE "int"
  
#undef  WCHAR_TYPE_SIZE
#define WCHAR_TYPE_SIZE BITS_PER_WORD
    
/* Provide a STARTFILE_SPEC appropriate for FreeBSD.  Here we add
   the magical crtbegin.o file (see crtstuff.c) which provides part 
	of the support for getting C++ file-scope static object constructed 
	before entering `main'.  */
   
#undef	STARTFILE_SPEC
#define STARTFILE_SPEC \
  "%{!shared: \
     %{pg:gcrt1.o%s} %{!pg:%{p:gcrt1.o%s} \
		       %{!p:%{profile:gcrt1.o%s} \
			 %{!profile:crt1.o%s}}}} \
   crti.o%s %{!shared:crtbegin.o%s} %{shared:crtbeginS.o%s}"

/* Provide a ENDFILE_SPEC appropriate for FreeBSD.  Here we tack on
   the magical crtend.o file (see crtstuff.c) which provides part of 
	the support for getting C++ file-scope static object constructed 
	before entering `main', followed by a normal "finalizer" file, 
	`crtn.o'.  */

#undef	ENDFILE_SPEC
#define ENDFILE_SPEC \
  "%{!shared:crtend.o%s} %{shared:crtendS.o%s} crtn.o%s"

/* Provide a LINK_SPEC appropriate for FreeBSD.  Here we provide support
   for the special GCC options -static and -shared, which allow us to
   link things in one of these three modes by applying the appropriate
   combinations of options at link-time. We like to support here for
   as many of the other GNU linker options as possible. But I don't
   have the time to search for those flags. I am sure how to add
   support for -soname shared_object_name. H.J.

   I took out %{v:%{!V:-V}}. It is too much :-(. They can use
   -Wl,-V.

   When the -shared link option is used a final link is not being
   done.  */

#undef	LINK_SPEC
#define LINK_SPEC "\
  %{Wl,*:%*} \
  %{v:-V} \
  %{assert*} %{R*} %{rpath*} %{defsym*} \
  %{shared:-Bshareable %{h*} %{soname*}} \
    %{!shared: \
      %{!static: \
        %{rdynamic:-export-dynamic} \
	%{!dynamic-linker:-dynamic-linker /usr/libexec/ld-elf.so.1}} \
    %{static:-Bstatic}} \
  %{symbolic:-Bsymbolic}"

/* A C statement to output to the stdio stream FILE an assembler
   command to advance the location counter to a multiple of 1<<LOG
   bytes if it is within MAX_SKIP bytes.

   This is used to align code labels according to Intel recommendations.  */

#ifdef HAVE_GAS_MAX_SKIP_P2ALIGN
#define ASM_OUTPUT_MAX_SKIP_ALIGN(FILE, LOG, MAX_SKIP)					\
  if ((LOG) != 0) {														\
    if ((MAX_SKIP) == 0) fprintf ((FILE), "\t.p2align %d\n", (LOG));	\
    else fprintf ((FILE), "\t.p2align %d,,%d\n", (LOG), (MAX_SKIP));	\
  }
#endif

/* Don't default to pcc-struct-return, we want to retain compatibility with
   older gcc versions AND pcc-struct-return is nonreentrant.
   (even though the SVR4 ABI for the i386 says that records and unions are
   returned in memory).  */

#undef  DEFAULT_PCC_STRUCT_RETURN
#define DEFAULT_PCC_STRUCT_RETURN 0

/* FreeBSD sets the rounding precision of the FPU to 53 bits.  Let the
   compiler get the contents of <float.h> and std::numeric_limits correct.  */
#define SUBTARGET_OVERRIDE_OPTIONS			\
  do {							\
    if (!TARGET_64BIT) {				\
      real_format_for_mode[XFmode - QFmode]		\
	= &ieee_extended_intel_96_round_53_format;	\
      real_format_for_mode[TFmode - QFmode]		\
	= &ieee_extended_intel_96_round_53_format;	\
    }							\
  } while (0)