1/* Function return value location for Linux/i386 ABI.
2   Copyright (C) 2005-2010, 2014 Red Hat, Inc.
3   This file is part of elfutils.
4
5   This file is free software; you can redistribute it and/or modify
6   it under the terms of either
7
8     * the GNU Lesser General Public License as published by the Free
9       Software Foundation; either version 3 of the License, or (at
10       your option) any later version
11
12   or
13
14     * the GNU General Public License as published by the Free
15       Software Foundation; either version 2 of the License, or (at
16       your option) any later version
17
18   or both in parallel, as here.
19
20   elfutils is distributed in the hope that it will be useful, but
21   WITHOUT ANY WARRANTY; without even the implied warranty of
22   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
23   General Public License for more details.
24
25   You should have received copies of the GNU General Public License and
26   the GNU Lesser General Public License along with this program.  If
27   not, see <http://www.gnu.org/licenses/>.  */
28
29#ifdef HAVE_CONFIG_H
30# include <config.h>
31#endif
32
33#include <assert.h>
34#include <dwarf.h>
35
36#define BACKEND i386_
37#include "libebl_CPU.h"
38
39
40/* %eax, or pair %eax, %edx.  */
41static const Dwarf_Op loc_intreg[] =
42  {
43    { .atom = DW_OP_reg0 }, { .atom = DW_OP_piece, .number = 4 },
44    { .atom = DW_OP_reg2 }, { .atom = DW_OP_piece, .number = 4 },
45  };
46#define nloc_intreg	1
47#define nloc_intregpair	4
48
49/* %st(0).  */
50static const Dwarf_Op loc_fpreg[] =
51  {
52    { .atom = DW_OP_reg11 }
53  };
54#define nloc_fpreg	1
55
56/* The return value is a structure and is actually stored in stack space
57   passed in a hidden argument by the caller.  But, the compiler
58   helpfully returns the address of that space in %eax.  */
59static const Dwarf_Op loc_aggregate[] =
60  {
61    { .atom = DW_OP_breg0, .number = 0 }
62  };
63#define nloc_aggregate 1
64
65int
66i386_return_value_location (Dwarf_Die *functypedie, const Dwarf_Op **locp)
67{
68  /* Start with the function's type, and get the DW_AT_type attribute,
69     which is the type of the return value.  */
70  Dwarf_Die die_mem, *typedie = &die_mem;
71  int tag = dwarf_peeled_die_type (functypedie, typedie);
72  if (tag <= 0)
73    return tag;
74
75  switch (tag)
76    {
77    case -1:
78      return -1;
79
80    case DW_TAG_subrange_type:
81      if (! dwarf_hasattr_integrate (typedie, DW_AT_byte_size))
82	{
83	  Dwarf_Attribute attr_mem, *attr;
84	  attr = dwarf_attr_integrate (typedie, DW_AT_type, &attr_mem);
85	  typedie = dwarf_formref_die (attr, &die_mem);
86	  tag = DWARF_TAG_OR_RETURN (typedie);
87	}
88      /* Fall through.  */
89
90    case DW_TAG_base_type:
91    case DW_TAG_enumeration_type:
92    case DW_TAG_pointer_type:
93    case DW_TAG_ptr_to_member_type:
94      {
95	Dwarf_Word size;
96	Dwarf_Attribute attr_mem;
97	if (dwarf_formudata (dwarf_attr_integrate (typedie, DW_AT_byte_size,
98						   &attr_mem), &size) != 0)
99	  {
100	    if (tag == DW_TAG_pointer_type || tag == DW_TAG_ptr_to_member_type)
101	      size = 4;
102	    else
103	      return -1;
104	  }
105	if (tag == DW_TAG_base_type)
106	  {
107	    Dwarf_Word encoding;
108	    if (dwarf_formudata (dwarf_attr_integrate (typedie, DW_AT_encoding,
109						       &attr_mem),
110				 &encoding) != 0)
111	      return -1;
112	    if (encoding == DW_ATE_float)
113	      {
114		if (size > 16)
115		  return -2;
116		*locp = loc_fpreg;
117		return nloc_fpreg;
118	      }
119	  }
120	*locp = loc_intreg;
121	if (size <= 4)
122	  return nloc_intreg;
123	if (size <= 8)
124	  return nloc_intregpair;
125
126	/* Else fall through.  */
127      }
128
129    case DW_TAG_structure_type:
130    case DW_TAG_class_type:
131    case DW_TAG_union_type:
132    case DW_TAG_array_type:
133      *locp = loc_aggregate;
134      return nloc_aggregate;
135    }
136
137  /* XXX We don't have a good way to return specific errors from ebl calls.
138     This value means we do not understand the type, but it is well-formed
139     DWARF and might be valid.  */
140  return -2;
141}
142