xref: /freebsd/contrib/elftoolchain/libdwarf/dwarf_child.3 (revision f6a3b357e9be4c6423c85eff9a847163a0d307c8) 
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25.\" $Id: dwarf_child.3 3644 2018-10-15 19:55:01Z jkoshy $
26.\"
27.Dd December 21, 2014
28.Dt DWARF_CHILD 3
29.Os
30.Sh NAME
31.Nm dwarf_child ,
32.Nm dwarf_offdie ,
33.Nm dwarf_offdie_b ,
34.Nm dwarf_siblingof ,
35.Nm dwarf_siblingof_b
36.Nd retrieve DWARF Debugging Information Entry descriptors
37.Sh LIBRARY
38.Lb libdwarf
39.Sh SYNOPSIS
40.In libdwarf.h
41.Ft int
42.Fn dwarf_child "Dwarf_Die die" "Dwarf_Die *ret_die" "Dwarf_Error *err"
43.Ft int
44.Fo dwarf_offdie
45.Fa "Dwarf_Debug dbg"
46.Fa "Dwarf_Off offset"
47.Fa "Dwarf_Die *ret_die"
48.Fa "Dwarf_Error *err"
49.Fc
50.Ft int
51.Fo dwarf_offdie_b
52.Fa "Dwarf_Debug dbg"
53.Fa "Dwarf_Off offset"
54.Fa "Dwarf_Bool is_info"
55.Fa "Dwarf_Die *ret_die"
56.Fa "Dwarf_Error *err"
57.Fc
58.Ft int
59.Fo dwarf_siblingof
60.Fa "Dwarf_Debug dbg"
61.Fa "Dwarf_Die die"
62.Fa "Dwarf_Die *ret_die"
63.Fa "Dwarf_Error *err"
64.Fc
65.Ft int
66.Fo dwarf_siblingof_b
67.Fa "Dwarf_Debug dbg"
68.Fa "Dwarf_Die die"
69.Fa "Dwarf_Die *ret_die"
70.Fa "Dwarf_Bool is_info"
71.Fa "Dwarf_Error *err"
72.Fc
73.Sh DESCRIPTION
74These functions are used to retrieve and traverse DWARF
75Debugging Information Entry (DIE) descriptors associated with
76a compilation unit.
77These descriptors are arranged in the form of a tree, traversable
78using
79.Dq child
80and
81.Dq sibling
82links; see
83.Xr dwarf 3
84for more information.
85DWARF Debugging Information Entry descriptors are represented
86by the
87.Vt Dwarf_Die
88opaque type.
89.Pp
90Function
91.Fn dwarf_child
92retrieves the child of descriptor denoted by argument
93.Ar die ,
94and stores it in the location pointed to by argument
95.Ar ret_die .
96.Pp
97Function
98.Fn dwarf_siblingof
99retrieves the sibling of the descriptor denoted by argument
100.Ar die ,
101and stores it in the location pointed to by argument
102.Ar ret_die .
103If argument
104.Ar die
105is NULL, the first debugging information entry descriptor for the
106current compilation unit will be returned.
107This function and function
108.Fn dwarf_child
109may be used together to traverse the tree of debugging information
110entry descriptors for a compilation unit.
111.Pp
112Function
113.Fn dwarf_siblingof_b
114is identical to the function
115.Fn dwarf_siblingof
116except that it can retrieve the sibling descriptor from either the
117current compilation unit or type unit.
118If argument
119.Ar is_info
120is non-zero, the function behaves identically to function
121.Fn dwarf_siblingof .
122If argument
123.Ar is_info
124is zero, the descriptor referred by argument
125.Ar die
126should be associated with a debugging information entry in the
127type unit.
128The function will store the sibling of the descriptor in the location
129pointed to by argument
130.Ar ret_die .
131If argument
132.Ar is_info
133is zero and argument
134.Ar die
135is
136.Dv NULL ,
137the first debugging information entry descriptor for the
138current type unit will be returned.
139.Pp
140Function
141.Fn dwarf_offdie
142retrieves the debugging information entry descriptor at global offset
143.Ar offset
144in the
145.Dq .debug_info
146section of the object associated with argument
147.Ar dbg .
148The returned descriptor is written to the location pointed to by argument
149.Ar ret_die .
150.Pp
151Function
152.Fn dwarf_offdie_b
153is identical to the function
154.Fn dwarf_offdie
155except that it can retrieve the debugging information entry descriptor at
156global offset
157.Ar offset
158from either of the
159.Dq .debug_info
160and
161.Dq .debug_types
162sections of the object associated with argument
163.Ar dbg .
164If argument
165.Ar is_info
166is non-zero, the function will retrieve the debugging information
167entry from the
168.Dq .debug_info
169section, otherwise the function will retrieve the debugging
170information entry from the
171.Dq .debug_types
172section.
173The returned descriptor is written to the location pointed to by argument
174.Ar ret_die .
175.Ss Memory Management
176The memory area used for the
177.Vt Dwarf_Die
178descriptor returned in argument
179.Ar ret_die
180is allocated by the
181.Lb libdwarf .
182Application code should use function
183.Fn dwarf_dealloc
184with the allocation type
185.Dv DW_DLA_DIE
186to free the memory area when the
187.Vt Dwarf_Die
188descriptor is no longer needed.
189.Sh RETURN VALUES
190These functions return the following values:
191.Bl -tag -width ".Bq Er DW_DLV_NO_ENTRY"
192.It Bq Er DW_DLV_OK
193The call succeeded.
194.It Bq Er DW_DLV_ERROR
195The requested operation failed.
196Additional information about the error encountered will be recorded in
197argument
198.Ar err ,
199if it is not NULL.
200.It Bq Er DW_DLV_NO_ENTRY
201For functions
202.Fn dwarf_child ,
203.Fn dwarf_siblingof
204and
205.Fn dwarf_siblingof_b ,
206the descriptor denoted by argument
207.Ar die
208did not have a child or sibling.
209.Pp
210For functions
211.Fn dwarf_offdie
212and
213.Fn dwarf_offdie_b ,
214there was no debugging information entry at the offset specified by
215argument
216.Ar offset .
217.El
218.Sh EXAMPLES
219To retrieve the first DWARF Debugging Information Entry descriptor for
220the first compilation unit associated with a
221.Vt Dwarf_Debug
222instance, and to traverse all its children, use:
223.Bd -literal -offset indent
224Dwarf_Debug dbg;
225Dwarf_Die die, die0;
226Dwarf_Error de;
227
228\&... allocate dbg using dwarf_init() etc ...
229
230if (dwarf_next_cu_header(dbg, NULL, NULL, NULL, NULL, NULL, &de) !=
231    DW_DLV_OK)
232	errx(EXIT_FAILURE, "dwarf_next_cu_header: %s",
233	    dwarf_errmsg(de));
234
235/* Get the first DIE for the current compilation unit. */
236die = NULL;
237if (dwarf_siblingof(dbg, die, &die0, &de) != DW_DLV_OK)
238	errx(EXIT_FAILURE, "dwarf_siblingof: %s", dwarf_errmsg(de));
239
240/* Get the first child of this DIE. */
241die = die0;
242if (dwarf_child(die, &die0, &de) != DW_DLV_OK)
243	errx(EXIT_FAILURE, "dwarf_child: %s", dwarf_errmsg(de));
244
245/* Get the rest of children. */
246do {
247	die = die0;
248	if (dwarf_siblingof(dbg, die, &die0, &de) == DW_DLV_ERROR)
249		errx(EXIT_FAILURE, "dwarf_siblingof: %s",
250		    dwarf_errmsg(de));
251} while (die0 != NULL);
252.Ed
253.Sh ERRORS
254These functions may fail with the following errors:
255.Bl -tag -width ".Bq Er DW_DLE_DIE_NO_CU_CONTEXT"
256.It Bq Er DW_DLE_ARGUMENT
257Arguments
258.Ar dbg ,
259.Ar die
260or
261.Ar ret_die
262were NULL.
263.It Bq Er DW_DLE_DIE_NO_CU_CONTEXT
264Argument
265.Ar dbg
266was not associated with a compilation unit.
267.It Bq Er DW_DLE_NO_ENTRY
268The descriptor denoted by argument
269.Ar die
270had no child or sibling, or there was no DWARF debugging information
271entry at the offset specified by argument
272.Va offset .
273.El
274.Sh SEE ALSO
275.Xr dwarf 3 ,
276.Xr dwarf_errmsg 3 ,
277.Xr dwarf_get_die_infotypes_flag 3 ,
278.Xr dwarf_next_cu_header 3
279