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);
16
18 backtrace() returns a backtrace for the calling program, in the array
19 pointed to by buffer. A backtrace is the series of currently active
20 function calls for the program. Each item in the array pointed to by
21 buffer is of type void *, and is the return address from the corre‐
22 sponding stack frame. The size argument specifies the maximum number
23 of addresses that can be stored in buffer. If the backtrace is larger
24 than size, then the addresses corresponding to the size most recent
25 function calls are returned; to obtain the complete backtrace, make
26 sure that buffer and size are large enough.
27 Given the set of addresses returned by backtrace() in buffer, back‐
29 trace_symbols() translates the addresses into an array of strings that
30 describe the addresses symbolically. The size argument specifies the
31 number of addresses in buffer. The symbolic representation of each ad‐
32 dress consists of the function name (if this can be determined), a
33 hexadecimal offset into the function, and the actual return address (in
34 hexadecimal). The address of the array of string pointers is returned
35 as the function result of backtrace_symbols(). This array is mal‐
36 loc(3)ed by backtrace_symbols(), and must be freed by the caller. (The
37 strings pointed to by the array of pointers need not and should not be
38 freed.)
39 backtrace_symbols_fd() takes the same buffer and size arguments as
41 backtrace_symbols(), but instead of returning an array of strings to
42 the caller, it writes the strings, one per line, to the file descriptor
43 fd. backtrace_symbols_fd() does not call malloc(3), and so can be em‐
44 ployed in situations where the latter function might fail, but see
45 NOTES.
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 For an explanation of the terms used in this section, see at‐
63 tributes(7).
64 ┌────────────────────────────────────────────┬───────────────┬─────────┐
66 │Interface │ Attribute │ Value │
67 ├────────────────────────────────────────────┼───────────────┼─────────┤
68 │backtrace(), backtrace_symbols(), │ Thread safety │ MT-Safe │
69 │backtrace_symbols_fd() │ │ │
70 └────────────────────────────────────────────┴───────────────┴─────────┘
71
73 These functions are GNU extensions.
74
76 These functions make some assumptions about how a function's return ad‐
77 dress is stored on the stack. Note the following:
78 * Omission of the frame pointers (as implied by any of gcc(1)'s non‐
80 zero optimization levels) may cause these assumptions to be violat‐
81 ed.
82 * Inlined functions do not have stack frames.
84 * Tail-call optimization causes one stack frame to replace another.
86 * backtrace() and backtrace_symbols_fd() don't call malloc() explicit‐
88 ly, but they are part of libgcc, which gets loaded dynamically when
89 first used. Dynamic loading usually triggers a call to malloc(3).
90 If you need certain calls to these two functions to not allocate
91 memory (in signal handlers, for example), you need to make sure
92 libgcc is loaded beforehand.
93 The symbol names may be unavailable without the use of special linker
95 options. For systems using the GNU linker, it is necessary to use the
96 -rdynamic linker option. Note that names of "static" functions are not
97 exposed, and won't be available in the backtrace.
98
100 The program below demonstrates the use of backtrace() and back‐
101 trace_symbols(). The following shell session shows what we might see
102 when running the program:
103 $ cc -rdynamic prog.c -o prog
105 $ ./prog 3
106 backtrace() returned 8 addresses
107 ./prog(myfunc3+0x5c) [0x80487f0]
108 ./prog [0x8048871]
109 ./prog(myfunc+0x21) [0x8048894]
110 ./prog(myfunc+0x1a) [0x804888d]
111 ./prog(myfunc+0x1a) [0x804888d]
112 ./prog(main+0x65) [0x80488fb]
113 /lib/libc.so.6(__libc_start_main+0xdc) [0xb7e38f9c]
114 ./prog [0x8048711]
115 Program source
117 #include <execinfo.h>
119 #include <stdio.h>
120 #include <stdlib.h>
121 #include <unistd.h>
122 #define BT_BUF_SIZE 100
124 void
126 myfunc3(void)
127 {
128 int nptrs;
129 void *buffer[BT_BUF_SIZE];
130 char **strings;
131 nptrs = backtrace(buffer, BT_BUF_SIZE);
133 printf("backtrace() returned %d addresses\n", nptrs);
134 /* The call backtrace_symbols_fd(buffer, nptrs, STDOUT_FILENO)
136 would produce similar output to the following: */
137 strings = backtrace_symbols(buffer, nptrs);
139 if (strings == NULL) {
140 perror("backtrace_symbols");
141 exit(EXIT_FAILURE);
142 }
143 for (int j = 0; j < nptrs; j++)
145 printf("%s\n", strings[j]);
146 free(strings);
148 }
149 static void /* "static" means don't export the symbol... */
151 myfunc2(void)
152 {
153 myfunc3();
154 }
155 void
157 myfunc(int ncalls)
158 {
159 if (ncalls > 1)
160 myfunc(ncalls - 1);
161 else
162 myfunc2();
163 }
164 int
166 main(int argc, char *argv[])
167 {
168 if (argc != 2) {
169 fprintf(stderr, "%s num-calls\n", argv[0]);
170 exit(EXIT_FAILURE);
171 }
172 myfunc(atoi(argv[1]));
174 exit(EXIT_SUCCESS);
175 }
176
178 addr2line(1), gcc(1), gdb(1), ld(1), dlopen(3), malloc(3)
179
181 This page is part of release 5.13 of the Linux man-pages project. A
182 description of the project, information about reporting bugs, and the
183 latest version of this page, can be found at
184 https://www.kernel.org/doc/man-pages/.
185GNU 2021-03-22 BACKTRACE(3)