1BACKTRACE(3) Linux Programmer's Manual BACKTRACE(3)
2
6 backtrace, backtrace_symbols, backtrace_symbols_fd - support for appli‐
7 cation self-debugging
8
10 #include <execinfo.h>
11 int backtrace(void **buffer, int size);
13 char **backtrace_symbols(void *const *buffer, int size);
15 void backtrace_symbols_fd(void *const *buffer, int size, int fd);
17
19 backtrace() returns a backtrace for the calling program, in the array
20 pointed to by buffer. A backtrace is the series of currently active
21 function calls for the program. Each item in the array pointed to by
22 buffer is of type void *, and is the return address from the corre‐
23 sponding stack frame. The size argument specifies the maximum number
24 of addresses that can be stored in buffer. If the backtrace is larger
25 than size, then the addresses corresponding to the size most recent
26 function calls are returned; to obtain the complete backtrace, make
27 sure that buffer and size are large enough.
28 Given the set of addresses returned by backtrace() in buffer, back‐
30 trace_symbols() translates the addresses into an array of strings that
31 describe the addresses symbolically. The size argument specifies the
32 number of addresses in buffer. The symbolic representation of each
33 address consists of the function name (if this can be determined), a
34 hexadecimal offset into the function, and the actual return address (in
35 hexadecimal). The address of the array of string pointers is returned
36 as the function result of backtrace_symbols(). This array is mal‐
37 loc(3)ed by backtrace_symbols(), and must be freed by the caller. (The
38 strings pointed to by the array of pointers need not and should not be
39 freed.)
40 backtrace_symbols_fd() takes the same buffer and size arguments as
42 backtrace_symbols(), but instead of returning an array of strings to
43 the caller, it writes the strings, one per line, to the file descriptor
44 fd. backtrace_symbols_fd() does not call malloc(3), and so can be
45 employed in situations where the latter function might fail, but see
46 NOTES.
47
49 backtrace() returns the number of addresses returned in buffer, which
50 is not greater than size. If the return value is less than size, then
51 the full backtrace was stored; if it is equal to size, then it may have
52 been truncated, in which case the addresses of the oldest stack frames
53 are not returned.
54 On success, backtrace_symbols() returns a pointer to the array mal‐
56 loc(3)ed by the call; on error, NULL is returned.
57
59 backtrace(), backtrace_symbols(), and backtrace_symbols_fd() are pro‐
60 vided in glibc since version 2.1.
61
63 For an explanation of the terms used in this section, see
64 attributes(7).
65 ┌───────────────────────┬───────────────┬─────────┐
67 │Interface │ Attribute │ Value │
68 ├───────────────────────┼───────────────┼─────────┤
69 │backtrace(), │ Thread safety │ MT-Safe │
70 │backtrace_symbols(), │ │ │
71 │backtrace_symbols_fd() │ │ │
72 └───────────────────────┴───────────────┴─────────┘
74 These functions are GNU extensions.
75
77 These functions make some assumptions about how a function's return
78 address is stored on the stack. Note the following:
79 * Omission of the frame pointers (as implied by any of gcc(1)'s
81 nonzero optimization levels) may cause these assumptions to be vio‐
82 lated.
83 * Inlined functions do not have stack frames.
85 * Tail-call optimization causes one stack frame to replace another.
87 * backtrace() and backtrace_symbols_fd() don't call malloc() explic‐
89 itly, but they are part of libgcc, which gets loaded dynamically
90 when first used. Dynamic loading usually triggers a call to mal‐
91 loc(3). If you need certain calls to these two functions to not
92 allocate memory (in signal handlers, for example), you need to make
93 sure libgcc is loaded beforehand.
94 The symbol names may be unavailable without the use of special linker
96 options. For systems using the GNU linker, it is necessary to use the
97 -rdynamic linker option. Note that names of "static" functions are not
98 exposed, and won't be available in the backtrace.
99
101 The program below demonstrates the use of backtrace() and back‐
102 trace_symbols(). The following shell session shows what we might see
103 when running the program:
104 $ cc -rdynamic prog.c -o prog
106 $ ./prog 3
107 backtrace() returned 8 addresses
108 ./prog(myfunc3+0x5c) [0x80487f0]
109 ./prog [0x8048871]
110 ./prog(myfunc+0x21) [0x8048894]
111 ./prog(myfunc+0x1a) [0x804888d]
112 ./prog(myfunc+0x1a) [0x804888d]
113 ./prog(main+0x65) [0x80488fb]
114 /lib/libc.so.6(__libc_start_main+0xdc) [0xb7e38f9c]
115 ./prog [0x8048711]
116 Program source
118 #include <execinfo.h>
120 #include <stdio.h>
121 #include <stdlib.h>
122 #include <unistd.h>
123 #define BT_BUF_SIZE 100
125 void
127 myfunc3(void)
128 {
129 int j, nptrs;
130 void *buffer[BT_BUF_SIZE];
131 char **strings;
132 nptrs = backtrace(buffer, BT_BUF_SIZE);
134 printf("backtrace() returned %d addresses\n", nptrs);
135 /* The call backtrace_symbols_fd(buffer, nptrs, STDOUT_FILENO)
137 would produce similar output to the following: */
138 strings = backtrace_symbols(buffer, nptrs);
140 if (strings == NULL) {
141 perror("backtrace_symbols");
142 exit(EXIT_FAILURE);
143 }
144 for (j = 0; j < nptrs; j++)
146 printf("%s\n", strings[j]);
147 free(strings);
149 }
150 static void /* "static" means don't export the symbol... */
152 myfunc2(void)
153 {
154 myfunc3();
155 }
156 void
158 myfunc(int ncalls)
159 {
160 if (ncalls > 1)
161 myfunc(ncalls - 1);
162 else
163 myfunc2();
164 }
165 int
167 main(int argc, char *argv[])
168 {
169 if (argc != 2) {
170 fprintf(stderr, "%s num-calls\n", argv[0]);
171 exit(EXIT_FAILURE);
172 }
173 myfunc(atoi(argv[1]));
175 exit(EXIT_SUCCESS);
176 }
177
179 addr2line(1), gcc(1), gdb(1), ld(1), dlopen(3), malloc(3)
180
182 This page is part of release 5.02 of the Linux man-pages project. A
183 description of the project, information about reporting bugs, and the
184 latest version of this page, can be found at
185 https://www.kernel.org/doc/man-pages/.
186GNU 2019-03-06 BACKTRACE(3)