varasm.c

gcc库的原代码,对编程有很大帮助.

      if (output_bytecode)
	bc_output_ascii (asm_out_file, p, thissize);
      else
	{
	  ASM_OUTPUT_ASCII (asm_out_file, p, thissize);
	}

      pos += thissize;
      p += thissize;
    }
}

static void
bc_output_ascii (file, p, size)
     FILE *file;
     char *p;
     int size;
{
  BC_OUTPUT_ASCII (file, p, size);
}

/* Assemble everything that is needed for a variable or function declaration.
   Not used for automatic variables, and not used for function definitions.
   Should not be called for variables of incomplete structure type.

   TOP_LEVEL is nonzero if this variable has file scope.
   AT_END is nonzero if this is the special handling, at end of compilation,
   to define things that have had only tentative definitions.
   DONT_OUTPUT_DATA if nonzero means don't actually output the
   initial value (that will be done by the caller).  */

void
assemble_variable (decl, top_level, at_end, dont_output_data)
     tree decl;
     int top_level;
     int at_end;
     int dont_output_data;
{
  register char *name;
  int align;
  tree size_tree;
  int reloc = 0;
  enum in_section saved_in_section;

  last_assemble_variable_decl = 0;

  if (output_bytecode)
    return;

  if (GET_CODE (DECL_RTL (decl)) == REG)
    {
      /* Do output symbol info for global register variables, but do nothing
	 else for them.  */

      if (TREE_ASM_WRITTEN (decl))
	return;
      TREE_ASM_WRITTEN (decl) = 1;

      if (!output_bytecode)
	{
#if defined (DBX_DEBUGGING_INFO) || defined (XCOFF_DEBUGGING_INFO)
	  /* File-scope global variables are output here.  */
	  if ((write_symbols == DBX_DEBUG || write_symbols == XCOFF_DEBUG)
	      && top_level)
	    dbxout_symbol (decl, 0);
#endif
#ifdef SDB_DEBUGGING_INFO
	  if (write_symbols == SDB_DEBUG && top_level
	      /* Leave initialized global vars for end of compilation;
		 see comment in compile_file.  */
	      && (TREE_PUBLIC (decl) == 0 || DECL_INITIAL (decl) == 0))
	    sdbout_symbol (decl, 0);
#endif
	}

      /* Don't output any DWARF debugging information for variables here.
	 In the case of local variables, the information for them is output
	 when we do our recursive traversal of the tree representation for
	 the entire containing function.  In the case of file-scope variables,
	 we output information for all of them at the very end of compilation
	 while we are doing our final traversal of the chain of file-scope
	 declarations.  */

      return;
    }

  /* Normally no need to say anything here for external references,
     since assemble_external is called by the language-specific code
     when a declaration is first seen.  */

  if (DECL_EXTERNAL (decl))
    return;

  /* Output no assembler code for a function declaration.
     Only definitions of functions output anything.  */

  if (TREE_CODE (decl) == FUNCTION_DECL)
    return;

  /* If type was incomplete when the variable was declared,
     see if it is complete now.  */

  if (DECL_SIZE (decl) == 0)
    layout_decl (decl, 0);

  /* Still incomplete => don't allocate it; treat the tentative defn
     (which is what it must have been) as an `extern' reference.  */

  if (!dont_output_data && DECL_SIZE (decl) == 0)
    {
      error_with_file_and_line (DECL_SOURCE_FILE (decl),
				DECL_SOURCE_LINE (decl),
				"storage size of `%s' isn't known",
				IDENTIFIER_POINTER (DECL_NAME (decl)));
      TREE_ASM_WRITTEN (decl) = 1;
      return;
    }

  /* The first declaration of a variable that comes through this function
     decides whether it is global (in C, has external linkage)
     or local (in C, has internal linkage).  So do nothing more
     if this function has already run.  */

  if (TREE_ASM_WRITTEN (decl))
    return;

  TREE_ASM_WRITTEN (decl) = 1;

  app_disable ();

  if (! dont_output_data)
    {
      if (TREE_CODE (DECL_SIZE (decl)) != INTEGER_CST)
	goto finish;

      /* This is better than explicit arithmetic, since it avoids overflow.  */
      size_tree = size_binop (CEIL_DIV_EXPR,
			  DECL_SIZE (decl), size_int (BITS_PER_UNIT));

      if (TREE_INT_CST_HIGH (size_tree) != 0)
	{
	  error_with_decl (decl, "size of variable `%s' is too large");
	  goto finish;
	}
    }

  name = XSTR (XEXP (DECL_RTL (decl), 0), 0);

  /* Handle uninitialized definitions.  */

  /* ANSI specifies that a tentative definition which is not merged with
     a non-tentative definition behaves exactly like a definition with an
     initializer equal to zero.  (Section 3.7.2)
     -fno-common gives strict ANSI behavior.  Usually you don't want it.
     This matters only for variables with external linkage.  */
  if ((! flag_no_common || ! TREE_PUBLIC (decl))
      && DECL_COMMON (decl)
      && ! dont_output_data
      && (DECL_INITIAL (decl) == 0 || DECL_INITIAL (decl) == error_mark_node))
    {
      int size = TREE_INT_CST_LOW (size_tree);
      int rounded = size;

      if (TREE_INT_CST_HIGH (size_tree) != 0)
	error_with_decl (decl, "size of variable `%s' is too large");
      /* Don't allocate zero bytes of common,
	 since that means "undefined external" in the linker.  */
      if (size == 0) rounded = 1;
      /* Round size up to multiple of BIGGEST_ALIGNMENT bits
	 so that each uninitialized object starts on such a boundary.  */
      rounded += (BIGGEST_ALIGNMENT / BITS_PER_UNIT) - 1;
      rounded = (rounded / (BIGGEST_ALIGNMENT / BITS_PER_UNIT)
		 * (BIGGEST_ALIGNMENT / BITS_PER_UNIT));

#ifdef DBX_DEBUGGING_INFO
      /* File-scope global variables are output here.  */
      if (write_symbols == DBX_DEBUG && top_level)
	dbxout_symbol (decl, 0);
#endif
#ifdef SDB_DEBUGGING_INFO
      if (write_symbols == SDB_DEBUG && top_level
	  /* Leave initialized global vars for end of compilation;
	     see comment in compile_file.  */
	  && (TREE_PUBLIC (decl) == 0 || DECL_INITIAL (decl) == 0))
	sdbout_symbol (decl, 0);
#endif

      /* Don't output any DWARF debugging information for variables here.
	 In the case of local variables, the information for them is output
	 when we do our recursive traversal of the tree representation for
	 the entire containing function.  In the case of file-scope variables,
	 we output information for all of them at the very end of compilation
	 while we are doing our final traversal of the chain of file-scope
	 declarations.  */

#if 0
      if (flag_shared_data)
	data_section ();
#endif
      if (TREE_PUBLIC (decl))
	{
#ifdef ASM_OUTPUT_SHARED_COMMON
	  if (flag_shared_data)
	    ASM_OUTPUT_SHARED_COMMON (asm_out_file, name, size, rounded);
	  else
#endif
	    if (output_bytecode)
	      {
		BC_OUTPUT_COMMON (asm_out_file, name, size, rounded);
	      }
	    else
	      {
#ifdef ASM_OUTPUT_ALIGNED_COMMON
		ASM_OUTPUT_ALIGNED_COMMON (asm_out_file, name, size,
					   DECL_ALIGN (decl));
#else
		ASM_OUTPUT_COMMON (asm_out_file, name, size, rounded);
#endif
	      }
	}
      else
	{
#ifdef ASM_OUTPUT_SHARED_LOCAL
	  if (flag_shared_data)
	    ASM_OUTPUT_SHARED_LOCAL (asm_out_file, name, size, rounded);
	  else
#endif
	    if (output_bytecode)
	      {
		BC_OUTPUT_LOCAL (asm_out_file, name, size, rounded);
	      }
	    else
	      {
#ifdef ASM_OUTPUT_ALIGNED_LOCAL
		ASM_OUTPUT_ALIGNED_LOCAL (asm_out_file, name, size,
					  DECL_ALIGN (decl));
#else
		ASM_OUTPUT_LOCAL (asm_out_file, name, size, rounded);
#endif
	      }
	}
      goto finish;
    }

  /* Handle initialized definitions.  */

  /* First make the assembler name(s) global if appropriate.  */
  if (TREE_PUBLIC (decl) && DECL_NAME (decl))
    {
      if (!first_global_object_name)
	{
	  char *p;

	  STRIP_NAME_ENCODING (p, name);
	  first_global_object_name = permalloc (strlen (p) + 1);
	  strcpy (first_global_object_name, p);
	}

#ifdef ASM_WEAKEN_LABEL
      if (DECL_WEAK (decl))
	ASM_WEAKEN_LABEL (asm_out_file, name);
      else
#endif
      ASM_GLOBALIZE_LABEL (asm_out_file, name);
    }
#if 0
  for (d = equivalents; d; d = TREE_CHAIN (d))
    {
      tree e = TREE_VALUE (d);
      if (TREE_PUBLIC (e) && DECL_NAME (e))
	ASM_GLOBALIZE_LABEL (asm_out_file,
			     XSTR (XEXP (DECL_RTL (e), 0), 0));
    }
#endif

  /* Output any data that we will need to use the address of.  */
  if (DECL_INITIAL (decl) == error_mark_node)
    reloc = contains_pointers_p (TREE_TYPE (decl));
  else if (DECL_INITIAL (decl))
    reloc = output_addressed_constants (DECL_INITIAL (decl));

  /* Switch to the proper section for this data.  */
  if (IN_NAMED_SECTION (decl))
    named_section (decl, NULL);
  else
    {
      /* C++ can have const variables that get initialized from constructors,
	 and thus can not be in a readonly section.  We prevent this by
	 verifying that the initial value is constant for objects put in a
	 readonly section.

	 error_mark_node is used by the C front end to indicate that the
	 initializer has not been seen yet.  In this case, we assume that
	 the initializer must be constant.  */
#ifdef SELECT_SECTION
      SELECT_SECTION (decl, reloc);
#else
      if (TREE_READONLY (decl)
	  && ! TREE_THIS_VOLATILE (decl)
	  && DECL_INITIAL (decl)
	  && (DECL_INITIAL (decl) == error_mark_node
	      || TREE_CONSTANT (DECL_INITIAL (decl)))
	  && ! (flag_pic && reloc))
	readonly_data_section ();
      else
	data_section ();
#endif
    }

  /* dbxout.c needs to know this.  */
  if (in_text_section ())
    DECL_IN_TEXT_SECTION (decl) = 1;

  /* Record current section so we can restore it if dbxout.c clobbers it.  */
  saved_in_section = in_section;

  /* Output the dbx info now that we have chosen the section.  */

#ifdef DBX_DEBUGGING_INFO
  /* File-scope global variables are output here.  */
  if (write_symbols == DBX_DEBUG && top_level)
    dbxout_symbol (decl, 0);
#endif
#ifdef SDB_DEBUGGING_INFO
  if (write_symbols == SDB_DEBUG && top_level
      /* Leave initialized global vars for end of compilation;
	 see comment in compile_file.  */
      && (TREE_PUBLIC (decl) == 0 || DECL_INITIAL (decl) == 0))
    sdbout_symbol (decl, 0);
#endif

  /* Don't output any DWARF debugging information for variables here.
     In the case of local variables, the information for them is output
     when we do our recursive traversal of the tree representation for
     the entire containing function.  In the case of file-scope variables,
     we output information for all of them at the very end of compilation
     while we are doing our final traversal of the chain of file-scope
     declarations.  */

  /* If the debugging output changed sections, reselect the section
     that's supposed to be selected.  */
  if (in_section != saved_in_section)
    {
      /* Switch to the proper section for this data.  */
#ifdef SELECT_SECTION
      SELECT_SECTION (decl, reloc);
#else
      if (TREE_READONLY (decl)
	  && ! TREE_THIS_VOLATILE (decl)
	  && DECL_INITIAL (decl)
	  && (DECL_INITIAL (decl) == error_mark_node
	      || TREE_CONSTANT (DECL_INITIAL (decl)))
	  && ! (flag_pic && reloc))
	readonly_data_section ();
      else
	data_section ();
#endif
    }

  /* Compute and output the alignment of this data.  */

  align = DECL_ALIGN (decl);
  /* In the case for initialing an array whose length isn't specified,
     where we have not yet been able to do the layout,
     figure out the proper alignment now.  */
  if (dont_output_data && DECL_SIZE (decl) == 0
      && TREE_CODE (TREE_TYPE (decl)) == ARRAY_TYPE)
    align = MAX (align, TYPE_ALIGN (TREE_TYPE (TREE_TYPE (decl))));

  /* Some object file formats have a maximum alignment which they support.
     In particular, a.out format supports a maximum alignment of 4.  */
#ifndef MAX_OFILE_ALIGNMENT
#define MAX_OFILE_ALIGNMENT BIGGEST_ALIGNMENT
#endif
  if (align > MAX_OFILE_ALIGNMENT)
    {
      warning_with_decl (decl,
	  "alignment of `%s' is greater than maximum object file alignment");
      align = MAX_OFILE_ALIGNMENT;
    }
#ifdef DATA_ALIGNMENT
  /* On some machines, it is good to increase alignment sometimes.  */
  align = DATA_ALIGNMENT (TREE_TYPE (decl), align);
#endif
#ifdef CONSTANT_ALIGNMENT
  if (DECL_INITIAL (decl))
    align = CONSTANT_ALIGNMENT (DECL_INITIAL (decl), align);
#endif

  /* Reset the alignment in case we have made it tighter, so we can benefit
     from it in get_pointer_alignment.  */
  DECL_ALIGN (decl) = align;

  if (align > BITS_PER_UNIT)
    {
      if (output_bytecode)
	BC_OUTPUT_ALIGN (asm_out_file, floor_log2 (align / BITS_PER_UNIT));
      else
	ASM_OUTPUT_ALIGN (asm_out_file, floor_log2 (align / BITS_PER_UNIT));
    }

  /* Do any machine/system dependent processing of the object.  */
#ifdef ASM_DECLARE_OBJECT_NAME
  last_assemble_variable_decl = decl;
  ASM_DECLARE_OBJECT_NAME (asm_out_file, name, decl);
#else
  /* Standard thing is just output label for the object.  */
  if (output_bytecode)
    BC_OUTPUT_LABEL (asm_out_file, name);
  else
    ASM_OUTPUT_LABEL (asm_out_file, name);
#endif /* ASM_DECLARE_OBJECT_NAME */

  if (!dont_output_data)
    {
      if (DECL_INITIAL (decl))
	/* Output the actual data.  */
	output_constant (DECL_INITIAL (decl), TREE_INT_CST_LOW (size_tree));
      else
	/* Leave space for it.  */
	assemble_zeros (TREE_INT_CST_LOW (size_tree));
    }

 finish:
#ifdef XCOFF_DEBUGGING_INFO
  /* Unfortunately, the IBM assembler cannot handle stabx before the actual
     declaration.  When something like ".stabx  "aa:S-2",aa,133,0" is emitted 
     and `aa' hasn't been output yet, the assembler generates a stab entry with
     a value of zero, in addition to creating an unnecessary external entry
     for `aa'.  Hence, we must postpone dbxout_symbol to here at the end.  */

  /* File-scope global variables are output here.  */
  if (write_symbols == XCOFF_DEBUG && top_level)
    {
      saved_in_section = in_section;

      dbxout_symbol (decl, 0);

      if (in_section != saved_in_section)
	{
	  /* Switch to the proper section for this data.  */
#ifdef SELECT_SECTION
	  SELECT_SECTION (decl, reloc);
#else
	  if (TREE_READONLY (decl)
	      && ! TREE_THIS_VOLATILE (decl)
	      && DECL_INITIAL (decl)
	      && (DECL_INITIAL (decl) == error_mark_node
		  || TREE_CONSTANT (DECL_INITIAL (decl)))
	      && ! (flag_pic && reloc))
	    readonly_data_section ();
	  else
	    data_section ();
#endif
	}
    }
#else
  /* There must be a statement after a label.  */
  ;
#endif
}

/* Return 1 if type TYPE contains any pointers.  */

static int
contains_pointers_p (type)
     tree type;
{