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      1 /* Function return value location for Linux/i386 ABI.
      2    Copyright (C) 2005, 2007 Red Hat, Inc.
      3    This file is part of Red Hat elfutils.
      4 
      5    Red Hat elfutils is free software; you can redistribute it and/or modify
      6    it under the terms of the GNU General Public License as published by the
      7    Free Software Foundation; version 2 of the License.
      8 
      9    Red Hat elfutils is distributed in the hope that it will be useful, but
     10    WITHOUT ANY WARRANTY; without even the implied warranty of
     11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     12    General Public License for more details.
     13 
     14    You should have received a copy of the GNU General Public License along
     15    with Red Hat elfutils; if not, write to the Free Software Foundation,
     16    Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301 USA.
     17 
     18    Red Hat elfutils is an included package of the Open Invention Network.
     19    An included package of the Open Invention Network is a package for which
     20    Open Invention Network licensees cross-license their patents.  No patent
     21    license is granted, either expressly or impliedly, by designation as an
     22    included package.  Should you wish to participate in the Open Invention
     23    Network licensing program, please visit www.openinventionnetwork.com
     24    <http://www.openinventionnetwork.com>.  */
     25 
     26 #ifdef HAVE_CONFIG_H
     27 # include <config.h>
     28 #endif
     29 
     30 #include <assert.h>
     31 #include <dwarf.h>
     32 
     33 #define BACKEND i386_
     34 #include "libebl_CPU.h"
     35 
     36 
     37 /* %eax, or pair %eax, %edx.  */
     38 static const Dwarf_Op loc_intreg[] =
     39   {
     40     { .atom = DW_OP_reg0 }, { .atom = DW_OP_piece, .number = 4 },
     41     { .atom = DW_OP_reg1 }, { .atom = DW_OP_piece, .number = 4 },
     42   };
     43 #define nloc_intreg	1
     44 #define nloc_intregpair	4
     45 
     46 /* %st(0).  */
     47 static const Dwarf_Op loc_fpreg[] =
     48   {
     49     { .atom = DW_OP_reg11 }
     50   };
     51 #define nloc_fpreg	1
     52 
     53 /* The return value is a structure and is actually stored in stack space
     54    passed in a hidden argument by the caller.  But, the compiler
     55    helpfully returns the address of that space in %eax.  */
     56 static const Dwarf_Op loc_aggregate[] =
     57   {
     58     { .atom = DW_OP_breg0, .number = 0 }
     59   };
     60 #define nloc_aggregate 1
     61 
     62 int
     63 i386_return_value_location (Dwarf_Die *functypedie, const Dwarf_Op **locp)
     64 {
     65   /* Start with the function's type, and get the DW_AT_type attribute,
     66      which is the type of the return value.  */
     67 
     68   Dwarf_Attribute attr_mem;
     69   Dwarf_Attribute *attr = dwarf_attr_integrate (functypedie, DW_AT_type,
     70 						&attr_mem);
     71   if (attr == NULL)
     72     /* The function has no return value, like a `void' function in C.  */
     73     return 0;
     74 
     75   Dwarf_Die die_mem;
     76   Dwarf_Die *typedie = dwarf_formref_die (attr, &die_mem);
     77   int tag = dwarf_tag (typedie);
     78 
     79   /* Follow typedefs and qualifiers to get to the actual type.  */
     80   while (tag == DW_TAG_typedef
     81 	 || tag == DW_TAG_const_type || tag == DW_TAG_volatile_type
     82 	 || tag == DW_TAG_restrict_type || tag == DW_TAG_mutable_type)
     83     {
     84       attr = dwarf_attr_integrate (typedie, DW_AT_type, &attr_mem);
     85       typedie = dwarf_formref_die (attr, &die_mem);
     86       tag = dwarf_tag (typedie);
     87     }
     88 
     89   switch (tag)
     90     {
     91     case -1:
     92       return -1;
     93 
     94     case DW_TAG_subrange_type:
     95       if (! dwarf_hasattr_integrate (typedie, DW_AT_byte_size))
     96 	{
     97 	  attr = dwarf_attr_integrate (typedie, DW_AT_type, &attr_mem);
     98 	  typedie = dwarf_formref_die (attr, &die_mem);
     99 	  tag = dwarf_tag (typedie);
    100 	}
    101       /* Fall through.  */
    102 
    103     case DW_TAG_base_type:
    104     case DW_TAG_enumeration_type:
    105     case DW_TAG_pointer_type:
    106     case DW_TAG_ptr_to_member_type:
    107       {
    108 	Dwarf_Word size;
    109 	if (dwarf_formudata (dwarf_attr_integrate (typedie, DW_AT_byte_size,
    110 						   &attr_mem), &size) != 0)
    111 	  {
    112 	    if (tag == DW_TAG_pointer_type || tag == DW_TAG_ptr_to_member_type)
    113 	      size = 4;
    114 	    else
    115 	      return -1;
    116 	  }
    117 	if (tag == DW_TAG_base_type)
    118 	  {
    119 	    Dwarf_Word encoding;
    120 	    if (dwarf_formudata (dwarf_attr_integrate (typedie, DW_AT_encoding,
    121 						       &attr_mem),
    122 				 &encoding) != 0)
    123 	      return -1;
    124 	    if (encoding == DW_ATE_float)
    125 	      {
    126 		if (size > 16)
    127 		  return -2;
    128 		*locp = loc_fpreg;
    129 		return nloc_fpreg;
    130 	      }
    131 	  }
    132 	*locp = loc_intreg;
    133 	if (size <= 4)
    134 	  return nloc_intreg;
    135 	if (size <= 8)
    136 	  return nloc_intregpair;
    137 
    138 	/* Else fall through.  */
    139       }
    140 
    141     case DW_TAG_structure_type:
    142     case DW_TAG_class_type:
    143     case DW_TAG_union_type:
    144     case DW_TAG_array_type:
    145       *locp = loc_aggregate;
    146       return nloc_aggregate;
    147     }
    148 
    149   /* XXX We don't have a good way to return specific errors from ebl calls.
    150      This value means we do not understand the type, but it is well-formed
    151      DWARF and might be valid.  */
    152   return -2;
    153 }
    154