sysv4.h

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

#undef	BITFIELD_NBYTES_LIMITED
#define	BITFIELD_NBYTES_LIMITED (TARGET_NO_BITFIELD_WORD)

/* Define this macro to be the value 1 if instructions will fail to
   work if given data not on the nominal alignment.  If instructions
   will merely go slower in that case, define this macro as 0.  */
#undef	STRICT_ALIGNMENT
#define	STRICT_ALIGNMENT (TARGET_STRICT_ALIGN)

/* Alignment in bits of the stack boundary.  Note, in order to allow building
   one set of libraries with -mno-eabi instead of eabi libraries and non-eabi
   versions, just use 64 as the stack boundary.  */
#undef	STACK_BOUNDARY
#define	STACK_BOUNDARY	(TARGET_ALTIVEC_ABI ? 128 : 64)

/* Real stack boundary as mandated by the appropriate ABI.  */
#define ABI_STACK_BOUNDARY ((TARGET_EABI && !TARGET_ALTIVEC_ABI) ? 64 : 128)

/* An expression for the alignment of a structure field FIELD if the
   alignment computed in the usual way is COMPUTED.  */
#define ADJUST_FIELD_ALIGN(FIELD, COMPUTED)				      \
	((TARGET_ALTIVEC && TREE_CODE (TREE_TYPE (FIELD)) == VECTOR_TYPE)     \
	 ? 128 : COMPUTED)

/* Define this macro as an expression for the alignment of a type
   (given by TYPE as a tree node) if the alignment computed in the
   usual way is COMPUTED and the alignment explicitly specified was
   SPECIFIED.  */
#define ROUND_TYPE_ALIGN(TYPE, COMPUTED, SPECIFIED)			\
	((TARGET_ALTIVEC  && TREE_CODE (TYPE) == VECTOR_TYPE)	        \
	 ? MAX (MAX ((COMPUTED), (SPECIFIED)), 128)                     \
         : MAX (COMPUTED, SPECIFIED))

#undef  BIGGEST_FIELD_ALIGNMENT

/* Use ELF style section commands.  */

#define	TEXT_SECTION_ASM_OP	"\t.section\t\".text\""

#define	DATA_SECTION_ASM_OP	"\t.section\t\".data\""

#define	BSS_SECTION_ASM_OP	"\t.section\t\".bss\""

/* Override elfos.h definition.  */
#undef	INIT_SECTION_ASM_OP
#define	INIT_SECTION_ASM_OP "\t.section\t\".init\",\"ax\""

/* Override elfos.h definition.  */
#undef	FINI_SECTION_ASM_OP
#define	FINI_SECTION_ASM_OP "\t.section\t\".fini\",\"ax\""

#define	TOC_SECTION_ASM_OP "\t.section\t\".got\",\"aw\""

/* Put PC relative got entries in .got2.  */
#define	MINIMAL_TOC_SECTION_ASM_OP \
  ((TARGET_RELOCATABLE || flag_pic) ? "\t.section\t\".got2\",\"aw\"" : "\t.section\t\".got1\",\"aw\"")

#define	SDATA_SECTION_ASM_OP "\t.section\t\".sdata\",\"aw\""
#define	SDATA2_SECTION_ASM_OP "\t.section\t\".sdata2\",\"a\""
#define	SBSS_SECTION_ASM_OP "\t.section\t\".sbss\",\"aw\",@nobits"

/* Besides the usual ELF sections, we need a toc section.  */
/* Override elfos.h definition.  */
#undef	EXTRA_SECTIONS
#define	EXTRA_SECTIONS in_toc, in_sdata, in_sdata2, in_sbss, in_init, in_fini

/* Override elfos.h definition.  */
#undef	EXTRA_SECTION_FUNCTIONS
#define	EXTRA_SECTION_FUNCTIONS						\
  TOC_SECTION_FUNCTION							\
  SDATA_SECTION_FUNCTION						\
  SDATA2_SECTION_FUNCTION						\
  SBSS_SECTION_FUNCTION							\
  INIT_SECTION_FUNCTION							\
  FINI_SECTION_FUNCTION

#define	TOC_SECTION_FUNCTION						\
void									\
toc_section ()								\
{									\
  if (in_section != in_toc)						\
    {									\
      in_section = in_toc;						\
      if (DEFAULT_ABI == ABI_AIX					\
	  && TARGET_MINIMAL_TOC						\
	  && !TARGET_RELOCATABLE)					\
	{								\
	  if (! toc_initialized)					\
	    {								\
	      toc_initialized = 1;					\
	      fprintf (asm_out_file, "%s\n", TOC_SECTION_ASM_OP);	\
	      ASM_OUTPUT_INTERNAL_LABEL (asm_out_file, "LCTOC", 0);	\
	      fprintf (asm_out_file, "\t.tc ");				\
	      ASM_OUTPUT_INTERNAL_LABEL_PREFIX (asm_out_file, "LCTOC1[TC],"); \
	      ASM_OUTPUT_INTERNAL_LABEL_PREFIX (asm_out_file, "LCTOC1"); \
	      fprintf (asm_out_file, "\n");				\
									\
	      fprintf (asm_out_file, "%s\n", MINIMAL_TOC_SECTION_ASM_OP); \
	      ASM_OUTPUT_INTERNAL_LABEL_PREFIX (asm_out_file, "LCTOC1"); \
	      fprintf (asm_out_file, " = .+32768\n");			\
	    }								\
	  else								\
	    fprintf (asm_out_file, "%s\n", MINIMAL_TOC_SECTION_ASM_OP);	\
	}								\
      else if (DEFAULT_ABI == ABI_AIX && !TARGET_RELOCATABLE)		\
	fprintf (asm_out_file, "%s\n", TOC_SECTION_ASM_OP);		\
      else								\
	{								\
	  fprintf (asm_out_file, "%s\n", MINIMAL_TOC_SECTION_ASM_OP);	\
	  if (! toc_initialized)					\
	    {								\
	      ASM_OUTPUT_INTERNAL_LABEL_PREFIX (asm_out_file, "LCTOC1"); \
	      fprintf (asm_out_file, " = .+32768\n");			\
	      toc_initialized = 1;					\
	    }								\
	}								\
    }									\
}									\
									\
extern int in_toc_section PARAMS ((void));				\
int in_toc_section ()							\
{									\
  return in_section == in_toc;						\
}

#define	SDATA_SECTION_FUNCTION						\
void									\
sdata_section ()							\
{									\
  if (in_section != in_sdata)						\
    {									\
      in_section = in_sdata;						\
      fprintf (asm_out_file, "%s\n", SDATA_SECTION_ASM_OP);		\
    }									\
}

#define	SDATA2_SECTION_FUNCTION						\
void									\
sdata2_section ()							\
{									\
  if (in_section != in_sdata2)						\
    {									\
      in_section = in_sdata2;						\
      fprintf (asm_out_file, "%s\n", SDATA2_SECTION_ASM_OP);		\
    }									\
}

#define	SBSS_SECTION_FUNCTION						\
void									\
sbss_section ()								\
{									\
  if (in_section != in_sbss)						\
    {									\
      in_section = in_sbss;						\
      fprintf (asm_out_file, "%s\n", SBSS_SECTION_ASM_OP);		\
    }									\
}

#define	INIT_SECTION_FUNCTION						\
void									\
init_section ()								\
{									\
  if (in_section != in_init)						\
    {									\
      in_section = in_init;						\
      fprintf (asm_out_file, "%s\n", INIT_SECTION_ASM_OP);		\
    }									\
}

#define	FINI_SECTION_FUNCTION						\
void									\
fini_section ()								\
{									\
  if (in_section != in_fini)						\
    {									\
      in_section = in_fini;						\
      fprintf (asm_out_file, "%s\n", FINI_SECTION_ASM_OP);		\
    }									\
}

/* Override default elf definitions.  */
#undef	TARGET_ASM_SELECT_RTX_SECTION
#define	TARGET_ASM_SELECT_RTX_SECTION rs6000_elf_select_rtx_section
#undef	TARGET_ASM_SELECT_SECTION
#define	TARGET_ASM_SELECT_SECTION  rs6000_elf_select_section
#define TARGET_ASM_UNIQUE_SECTION  rs6000_elf_unique_section

/* Return nonzero if this entry is to be written into the constant pool
   in a special way.  We do so if this is a SYMBOL_REF, LABEL_REF or a CONST
   containing one of them.  If -mfp-in-toc (the default), we also do
   this for floating-point constants.  We actually can only do this
   if the FP formats of the target and host machines are the same, but
   we can't check that since not every file that uses
   GO_IF_LEGITIMATE_ADDRESS_P includes real.h.

   Unlike AIX, we don't key off of -mminimal-toc, but instead do not
   allow floating point constants in the TOC if -mrelocatable.  */

#undef	ASM_OUTPUT_SPECIAL_POOL_ENTRY_P
#define	ASM_OUTPUT_SPECIAL_POOL_ENTRY_P(X, MODE)			\
  (TARGET_TOC								\
   && (GET_CODE (X) == SYMBOL_REF					\
       || (GET_CODE (X) == CONST && GET_CODE (XEXP (X, 0)) == PLUS	\
	   && GET_CODE (XEXP (XEXP (X, 0), 0)) == SYMBOL_REF)		\
       || GET_CODE (X) == LABEL_REF					\
       || (GET_CODE (X) == CONST_INT 					\
	   && GET_MODE_BITSIZE (MODE) <= GET_MODE_BITSIZE (Pmode))	\
       || (!TARGET_NO_FP_IN_TOC						\
	   && !TARGET_RELOCATABLE					\
	   && GET_CODE (X) == CONST_DOUBLE				\
	   && GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT		\
	   && BITS_PER_WORD == HOST_BITS_PER_INT)))

/* These macros generate the special .type and .size directives which
   are used to set the corresponding fields of the linker symbol table
   entries in an ELF object file under SVR4.  These macros also output
   the starting labels for the relevant functions/objects.  */

/* Write the extra assembler code needed to declare a function properly.
   Some svr4 assemblers need to also have something extra said about the
   function's return value.  We allow for that here.  */

extern int rs6000_pic_labelno;

/* Override elfos.h definition.  */
#undef	ASM_DECLARE_FUNCTION_NAME
#define ASM_DECLARE_FUNCTION_NAME(FILE, NAME, DECL)			\
  do {									\
    const char *const init_ptr = (TARGET_64BIT) ? ".quad" : ".long";	\
									\
    if (TARGET_RELOCATABLE 						\
	&& (get_pool_size () != 0 || current_function_profile)		\
	&& uses_TOC())							\
      {									\
	char buf[256];							\
									\
	ASM_OUTPUT_INTERNAL_LABEL (FILE, "LCL", rs6000_pic_labelno);	\
									\
	ASM_GENERATE_INTERNAL_LABEL (buf, "LCTOC", 1);			\
	fprintf (FILE, "\t%s ", init_ptr);				\
	assemble_name (FILE, buf);					\
	putc ('-', FILE);						\
	ASM_GENERATE_INTERNAL_LABEL (buf, "LCF", rs6000_pic_labelno);	\
	assemble_name (FILE, buf);					\
	putc ('\n', FILE);						\
      }									\
									\
    ASM_OUTPUT_TYPE_DIRECTIVE (FILE, NAME, "function");			\
    ASM_DECLARE_RESULT (FILE, DECL_RESULT (DECL));			\
									\
    if (DEFAULT_ABI == ABI_AIX)						\
      {									\
	const char *desc_name, *orig_name;				\
									\
        orig_name = (*targetm.strip_name_encoding) (NAME);		\
        desc_name = orig_name;						\
	while (*desc_name == '.')					\
	  desc_name++;							\
									\
	if (TREE_PUBLIC (DECL))						\
	  fprintf (FILE, "\t.globl %s\n", desc_name);			\
									\
	fprintf (FILE, "%s\n", MINIMAL_TOC_SECTION_ASM_OP);		\
	fprintf (FILE, "%s:\n", desc_name);				\
	fprintf (FILE, "\t%s %s\n", init_ptr, orig_name);		\
	fprintf (FILE, "\t%s _GLOBAL_OFFSET_TABLE_\n", init_ptr);	\
	if (DEFAULT_ABI == ABI_AIX)					\
	  fprintf (FILE, "\t%s 0\n", init_ptr);				\
	fprintf (FILE, "\t.previous\n");				\
      }									\
    ASM_OUTPUT_LABEL (FILE, NAME);					\
  } while (0)

/* The USER_LABEL_PREFIX stuff is affected by the -fleading-underscore
   flag.  The LOCAL_LABEL_PREFIX variable is used by dbxelf.h.  */

#define	LOCAL_LABEL_PREFIX "."
#define	USER_LABEL_PREFIX ""

/* svr4.h overrides ASM_OUTPUT_INTERNAL_LABEL.  */

#define	ASM_OUTPUT_INTERNAL_LABEL_PREFIX(FILE,PREFIX)	\
  asm_fprintf (FILE, "%L%s", PREFIX)

/* Globalizing directive for a label.  */
#define GLOBAL_ASM_OP "\t.globl "

/* This says how to output assembler code to declare an
   uninitialized internal linkage data object.  Under SVR4,
   the linker seems to want the alignment of data objects
   to depend on their types.  We do exactly that here.  */

#define	LOCAL_ASM_OP	"\t.local\t"

#define	LCOMM_ASM_OP	"\t.lcomm\t"

/* Override elfos.h definition.  */
#undef	ASM_OUTPUT_ALIGNED_LOCAL
#define	ASM_OUTPUT_ALIGNED_LOCAL(FILE, NAME, SIZE, ALIGN)		\
do {									\
  if (rs6000_sdata != SDATA_NONE && (SIZE) > 0				\
      && (SIZE) <= g_switch_value)					\
    {									\
      sbss_section ();							\
      ASM_OUTPUT_ALIGN (FILE, exact_log2 (ALIGN / BITS_PER_UNIT));	\
      ASM_OUTPUT_LABEL (FILE, NAME);					\
      ASM_OUTPUT_SKIP (FILE, SIZE);					\
      if (!flag_inhibit_size_directive && (SIZE) > 0)			\
	ASM_OUTPUT_SIZE_DIRECTIVE (FILE, NAME, SIZE);			\
    }									\
  else									\
    {									\
      fprintf (FILE, "%s", LCOMM_ASM_OP);				\
      assemble_name ((FILE), (NAME));					\
      fprintf ((FILE), ",%u,%u\n", (SIZE), (ALIGN) / BITS_PER_UNIT);	\
    }									\
  ASM_OUTPUT_TYPE_DIRECTIVE (FILE, NAME, "object");			\
} while (0)

/* Describe how to emit uninitialized external linkage items.  */
#define	ASM_OUTPUT_ALIGNED_BSS(FILE, DECL, NAME, SIZE, ALIGN)		\
do {									\
  ASM_OUTPUT_ALIGNED_LOCAL (FILE, NAME, SIZE, ALIGN);			\
} while (0)

/* This is how to output code to push a register on the stack.
   It need not be very fast code.

   On the rs6000, we must keep the backchain up to date.  In order
   to simplify things, always allocate 16 bytes for a push (System V
   wants to keep stack aligned to a 16 byte boundary).  */

#define	ASM_OUTPUT_REG_PUSH(FILE, REGNO)				\
do {									\
  if (DEFAULT_ABI == ABI_V4)						\
    asm_fprintf (FILE,							\
		 "\t{stu|stwu} %s,-16(%s)\n\t{st|stw} %s,12(%s)\n",	\
		 reg_names[1], reg_names[1], reg_names[REGNO],		\
		 reg_names[1]);						\
} while (0)

/* This is how to output an insn to pop a register from the stack.
   It need not be very fast code.  */

#define	ASM_OUTPUT_REG_POP(FILE, REGNO)					\
do {									\
  if (DEFAULT_ABI == ABI_V4)						\
    asm_fprintf (FILE,							\
		 "\t{l|lwz} %s,12(%s)\n\t{ai|addic} %s,%s,16\n",	\
		 reg_names[REGNO], reg_names[1], reg_names[1],		\
		 reg_names[1]);						\
} while (0)

/* Switch  Recognition by gcc.c.  Add -G xx support.  */

/* Override svr4.h definition.  */
#undef	SWITCH_TAKES_ARG
#define	SWITCH_TAKES_ARG(CHAR)						\
  ((CHAR) == 'D' || (CHAR) == 'U' || (CHAR) == 'o'			\
   || (CHAR) == 'e' || (CHAR) == 'T' || (CHAR) == 'u'			\
   || (CHAR) == 'I' || (CHAR) == 'm' || (CHAR) == 'x'			\
   || (CHAR) == 'L' || (CHAR) == 'A' || (CHAR) == 'V'			\
   || (CHAR) == 'B' || (CHAR) == 'b' || (CHAR) == 'G')

/* Output .file.  */
/* Override elfos.h definition.  */
#undef	ASM_FILE_START
#define	ASM_FILE_START(FILE)						\
do {									\
  output_file_directive ((FILE), main_input_filename);			\