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1 /* Return child of current DIE.
2    Copyright (C) 2003-2011, 2014, 2017 Red Hat, Inc.
3    This file is part of elfutils.
4    Written by Ulrich Drepper <drepper@redhat.com>, 2003.
5 
6    This file is free software; you can redistribute it and/or modify
7    it under the terms of either
8 
9      * the GNU Lesser General Public License as published by the Free
10        Software Foundation; either version 3 of the License, or (at
11        your option) any later version
12 
13    or
14 
15      * the GNU General Public License as published by the Free
16        Software Foundation; either version 2 of the License, or (at
17        your option) any later version
18 
19    or both in parallel, as here.
20 
21    elfutils is distributed in the hope that it will be useful, but
22    WITHOUT ANY WARRANTY; without even the implied warranty of
23    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
24    General Public License for more details.
25 
26    You should have received copies of the GNU General Public License and
27    the GNU Lesser General Public License along with this program.  If
28    not, see <http://www.gnu.org/licenses/>.  */
29 
30 #ifdef HAVE_CONFIG_H
31 # include <config.h>
32 #endif
33 
34 #include "libdwP.h"
35 #include <string.h>
36 
37 /* Some arbitrary value not conflicting with any existing code.  */
38 #define INVALID 0xffffe444
39 
40 
41 unsigned char *
42 internal_function
__libdw_find_attr(Dwarf_Die * die,unsigned int search_name,unsigned int * codep,unsigned int * formp)43 __libdw_find_attr (Dwarf_Die *die, unsigned int search_name,
44 		   unsigned int *codep, unsigned int *formp)
45 {
46   const unsigned char *readp = NULL;
47 
48   /* Find the abbreviation entry.  */
49   Dwarf_Abbrev *abbrevp = __libdw_dieabbrev (die, &readp);
50   if (unlikely (abbrevp == DWARF_END_ABBREV))
51     {
52       __libdw_seterrno (DWARF_E_INVALID_DWARF);
53       return NULL;
54     }
55 
56   /* Search the name attribute.  Attribute has been checked when
57      Dwarf_Abbrev was created, we can read unchecked.  */
58   const unsigned char *attrp = abbrevp->attrp;
59   while (1)
60     {
61       /* Get attribute name and form.  */
62       unsigned int attr_name;
63       get_uleb128_unchecked (attr_name, attrp);
64 
65       unsigned int attr_form;
66       get_uleb128_unchecked (attr_form, attrp);
67 
68       /* We can stop if we found the attribute with value zero.  */
69       if (attr_name == 0 && attr_form == 0)
70 	break;
71 
72       /* Is this the name attribute?  */
73       if (attr_name == search_name && search_name != INVALID)
74 	{
75 	  if (codep != NULL)
76 	    *codep = attr_name;
77 	  if (formp != NULL)
78 	    *formp = attr_form;
79 
80 	  /* Normally the attribute data comes from the DIE/info,
81 	     except for implicit_form, where it comes from the abbrev.  */
82 	  if (attr_form == DW_FORM_implicit_const)
83 	    return (unsigned char *) attrp;
84 	  else
85 	    return (unsigned char *) readp;
86 	}
87 
88       /* Skip over the rest of this attribute (if there is any).  */
89       if (attr_form != 0)
90 	{
91 	  size_t len = __libdw_form_val_len (die->cu, attr_form, readp);
92 	  if (unlikely (len == (size_t) -1l))
93 	    {
94 	      readp = NULL;
95 	      break;
96 	    }
97 
98 	  // __libdw_form_val_len will have done a bounds check.
99 	  readp += len;
100 
101 	  // If the value is in the abbrev data, skip it.
102 	  if (attr_form == DW_FORM_implicit_const)
103 	    {
104 	      int64_t attr_value __attribute__((__unused__));
105 	      get_sleb128_unchecked (attr_value, attrp);
106 	    }
107 	}
108     }
109 
110   // XXX Do we need other values?
111   if (codep != NULL)
112     *codep = INVALID;
113   if (formp != NULL)
114     *formp = INVALID;
115 
116   return (unsigned char *) readp;
117 }
118 
119 
120 int
dwarf_child(Dwarf_Die * die,Dwarf_Die * result)121 dwarf_child (Dwarf_Die *die, Dwarf_Die *result)
122 {
123   /* Ignore previous errors.  */
124   if (die == NULL)
125     return -1;
126 
127   /* Find the abbreviation entry.  */
128   Dwarf_Abbrev *abbrevp = __libdw_dieabbrev (die, NULL);
129   if (unlikely (abbrevp == DWARF_END_ABBREV))
130     {
131       __libdw_seterrno (DWARF_E_INVALID_DWARF);
132       return -1;
133     }
134 
135   /* If there are no children, do not search.  */
136   if (! abbrevp->has_children)
137     return 1;
138 
139   /* Skip past the last attribute.  */
140   void *addr = __libdw_find_attr (die, INVALID, NULL, NULL);
141 
142   if (addr == NULL)
143     return -1;
144 
145   /* RESULT can be the same as DIE.  So preserve what we need.  */
146   struct Dwarf_CU *cu = die->cu;
147 
148   /* It's kosher (just suboptimal) to have a null entry first thing (7.5.3).
149      So if this starts with ULEB128 of 0 (even with silly encoding of 0),
150      it is a kosher null entry and we do not really have any children.  */
151   const unsigned char *code = addr;
152   const unsigned char *endp = cu->endp;
153   while (1)
154     {
155       if (unlikely (code >= endp)) /* Truncated section.  */
156 	return 1;
157       if (unlikely (*code == 0x80))
158 	++code;
159       else
160 	break;
161     }
162   if (unlikely (*code == '\0'))
163     return 1;
164 
165   /* Clear the entire DIE structure.  This signals we have not yet
166      determined any of the information.  */
167   memset (result, '\0', sizeof (Dwarf_Die));
168 
169   /* We have the address.  */
170   result->addr = addr;
171 
172   /* Same CU as the parent.  */
173   result->cu = cu;
174 
175   return 0;
176 }
177 INTDEF(dwarf_child)
178