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.
46
48 backtrace() returns the number of addresses returned in buffer, which
49 is not greater than size. If the return value is less than size, then
50 the full backtrace was stored; if it is equal to size, then it may have
51 been truncated, in which case the addresses of the oldest stack frames
52 are not returned.
53 On success, backtrace_symbols() returns a pointer to the array mal‐
55 loc(3)ed by the call; on error, NULL is returned.
56
58 backtrace(), backtrace_symbols(), and backtrace_symbols_fd() are pro‐
59 vided in glibc since version 2.1.
60
62 These functions are GNU extensions.
63
65 These functions make some assumptions about how a function's return
66 address is stored on the stack. Note the following:
67 * Omission of the frame pointers (as implied by any of gcc(1)'s non-
69 zero optimization levels) may cause these assumptions to be vio‐
70 lated.
71 * Inlined functions do not have stack frames.
73 * Tail-call optimization causes one stack frame to replace another.
75 The symbol names may be unavailable without the use of special linker
77 options. For systems using the GNU linker, it is necessary to use the
78 -rdynamic linker option. Note that names of "static" functions are not
79 exposed, and won't be available in the backtrace.
80
82 The program below demonstrates the use of backtrace() and back‐
83 trace_symbols(). The following shell session shows what we might see
84 when running the program:
85 $ cc -rdynamic prog.c -o prog
87 $ ./prog 3
88 backtrace() returned 8 addresses
89 ./prog(myfunc3+0x5c) [0x80487f0]
90 ./prog [0x8048871]
91 ./prog(myfunc+0x21) [0x8048894]
92 ./prog(myfunc+0x1a) [0x804888d]
93 ./prog(myfunc+0x1a) [0x804888d]
94 ./prog(main+0x65) [0x80488fb]
95 /lib/libc.so.6(__libc_start_main+0xdc) [0xb7e38f9c]
96 ./prog [0x8048711]
97 Program source
99 #include <execinfo.h>
101 #include <stdio.h>
102 #include <stdlib.h>
103 #include <unistd.h>
104 void
106 myfunc3(void)
107 {
108 int j, nptrs;
109 #define SIZE 100
110 void *buffer[100];
111 char **strings;
112 nptrs = backtrace(buffer, SIZE);
114 printf("backtrace() returned %d addresses\n", nptrs);
115 /* The call backtrace_symbols_fd(buffer, nptrs, STDOUT_FILENO)
117 would produce similar output to the following: */
118 strings = backtrace_symbols(buffer, nptrs);
120 if (strings == NULL) {
121 perror("backtrace_symbols");
122 exit(EXIT_FAILURE);
123 }
124 for (j = 0; j < nptrs; j++)
126 printf("%s\n", strings[j]);
127 free(strings);
129 }
130 static void /* "static" means don't export the symbol... */
132 myfunc2(void)
133 {
134 myfunc3();
135 }
136 void
138 myfunc(int ncalls)
139 {
140 if (ncalls > 1)
141 myfunc(ncalls - 1);
142 else
143 myfunc2();
144 }
145 int
147 main(int argc, char *argv[])
148 {
149 if (argc != 2) {
150 fprintf(stderr, "%s num-calls\n", argv[0]);
151 exit(EXIT_FAILURE);
152 }
153 myfunc(atoi(argv[1]));
155 exit(EXIT_SUCCESS);
156 }
157
159 gcc(1), ld(1), dlopen(3), malloc(3)
160
162 This page is part of release 3.22 of the Linux man-pages project. A
163 description of the project, and information about reporting bugs, can
164 be found at http://www.kernel.org/doc/man-pages/.
165GNU 2008-06-14 BACKTRACE(3)