1/* Function return value location for Linux/PPC ABI.
2   Copyright (C) 2005, 2006, 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 ppc_
34#include "libebl_CPU.h"
35
36
37/* This is the SVR4 ELF ABI convention, but AIX and Linux do not use it.  */
38#define SVR4_STRUCT_RETURN 0
39
40
41/* r3, or pair r3, r4.  */
42static const Dwarf_Op loc_intreg[] =
43  {
44    { .atom = DW_OP_reg3 }, { .atom = DW_OP_piece, .number = 4 },
45    { .atom = DW_OP_reg4 }, { .atom = DW_OP_piece, .number = 4 },
46  };
47#define nloc_intreg	1
48#define nloc_intregpair	4
49
50/* f1.  */
51static const Dwarf_Op loc_fpreg[] =
52  {
53    { .atom = DW_OP_regx, .number = 33 }
54  };
55#define nloc_fpreg	1
56
57/* The return value is a structure and is actually stored in stack space
58   passed in a hidden argument by the caller.  But, the compiler
59   helpfully returns the address of that space in r3.  */
60static const Dwarf_Op loc_aggregate[] =
61  {
62    { .atom = DW_OP_breg3, .number = 0 }
63  };
64#define nloc_aggregate 1
65
66
67int
68ppc_return_value_location (Dwarf_Die *functypedie, const Dwarf_Op **locp)
69{
70  /* Start with the function's type, and get the DW_AT_type attribute,
71     which is the type of the return value.  */
72
73  Dwarf_Attribute attr_mem;
74  Dwarf_Attribute *attr = dwarf_attr_integrate (functypedie, DW_AT_type,
75						&attr_mem);
76  if (attr == NULL)
77    /* The function has no return value, like a `void' function in C.  */
78    return 0;
79
80  Dwarf_Die die_mem;
81  Dwarf_Die *typedie = dwarf_formref_die (attr, &die_mem);
82  int tag = dwarf_tag (typedie);
83
84  /* Follow typedefs and qualifiers to get to the actual type.  */
85  while (tag == DW_TAG_typedef
86	 || tag == DW_TAG_const_type || tag == DW_TAG_volatile_type
87	 || tag == DW_TAG_restrict_type || tag == DW_TAG_mutable_type)
88    {
89      attr = dwarf_attr_integrate (typedie, DW_AT_type, &attr_mem);
90      typedie = dwarf_formref_die (attr, &die_mem);
91      tag = dwarf_tag (typedie);
92    }
93
94  Dwarf_Word size;
95  switch (tag)
96    {
97    case -1:
98      return -1;
99
100    case DW_TAG_subrange_type:
101      if (! dwarf_hasattr_integrate (typedie, DW_AT_byte_size))
102	{
103	  attr = dwarf_attr_integrate (typedie, DW_AT_type, &attr_mem);
104	  typedie = dwarf_formref_die (attr, &die_mem);
105	  tag = dwarf_tag (typedie);
106	}
107      /* Fall through.  */
108
109    case DW_TAG_base_type:
110    case DW_TAG_enumeration_type:
111    case DW_TAG_pointer_type:
112    case DW_TAG_ptr_to_member_type:
113      if (dwarf_formudata (dwarf_attr_integrate (typedie, DW_AT_byte_size,
114						 &attr_mem), &size) != 0)
115	{
116	  if (tag == DW_TAG_pointer_type || tag == DW_TAG_ptr_to_member_type)
117	    size = 4;
118	  else
119	    return -1;
120	}
121      if (size <= 8)
122	{
123	  if (tag == DW_TAG_base_type)
124	    {
125	      Dwarf_Word encoding;
126	      if (dwarf_formudata (dwarf_attr_integrate (typedie,
127							 DW_AT_encoding,
128							 &attr_mem),
129				   &encoding) != 0)
130		return -1;
131	      if (encoding == DW_ATE_float)
132		{
133		  *locp = loc_fpreg;
134		  return nloc_fpreg;
135		}
136	    }
137	intreg:
138	  *locp = loc_intreg;
139	  return size <= 4 ? nloc_intreg : nloc_intregpair;
140	}
141
142    aggregate:
143      *locp = loc_aggregate;
144      return nloc_aggregate;
145
146    case DW_TAG_structure_type:
147    case DW_TAG_class_type:
148    case DW_TAG_union_type:
149    case DW_TAG_array_type:
150      if (SVR4_STRUCT_RETURN
151	  && dwarf_formudata (dwarf_attr_integrate (typedie, DW_AT_byte_size,
152						    &attr_mem), &size) == 0
153	  && size > 0 && size <= 8)
154	goto intreg;
155      goto aggregate;
156    }
157
158  /* XXX We don't have a good way to return specific errors from ebl calls.
159     This value means we do not understand the type, but it is well-formed
160     DWARF and might be valid.  */
161  return -2;
162}
163