Is there any way to dump the call stack in a running process in C or C++ every time a certain function is called? What I have in mind is something like this:
void foo()
{
print_stack_trace();
// foo's body
return
}
Where print_stack_trace works similarly to caller in Perl.
Or something like this:
int main (void)
{
// will print out debug info every time foo() is called
register_stack_trace_function(foo);
// etc...
}
where register_stack_trace_function puts some sort of internal breakpoint that will cause a stack trace to be printed whenever foo is called.
Does anything like this exist in some standard C library?
I am working on Linux, using GCC.
Background
I have a test run that behaves differently based on some commandline switches that shouldn't affect this behavior. My code has a pseudo-random number generator that I assume is being called differently based on these switches. I want to be able to run the test with each set of switches and see if the random number generator is called differently for each one.
Survey of C/C++ backtrace methods
In this answer I will try to run a single benchmark for a bunch of solutions to see which one runs faster, while also considering other points such as features and portability.
Tool
Time / call
Line number
Function name
C++ demangling
Recompile
Signal safe
As string
C
C++23 <stacktrace> GCC 12.1
7 us
y
y
y
y
n
y
n
Boost 1.74 stacktrace()
5 us
y
y
y
y
n
y
n
Boost 1.74 stacktrace::safe_dump_to
y
n
n
glibc backtrace_symbols_fd
25 us
n
-rdynamic
hacks
y
y
n
y
glibc backtrace_symbols
21 us
n
-rdynamic
hacks
y
n
y
y
GDB scripting
600 us
y
y
y
n
y
n
y
GDB code injection
n
n
y
libunwind
y
libdwfl
4 ms
n
y
libbacktrace
y
Empty cells mean "TODO", not "no".
us: microsecond
Line number: shows actual line number, not just function name + a memory address.
It is usually possible to recover the line number from an address manually after the fact with addr2line. But it is a pain.
Recompile: requires recompiling the program to get your traces. Not recompiling is better!
Signal safe: crucial for the important uses case of "getting a stack trace in case of segfault": How to automatically generate a stacktrace when my program crashes
As string: you get the stack trace as a string in the program itself, as opposed to e.g. just printing to stdout. Usually implies not signal safe, as we don't know the size of the stack trace string size in advance, and therefore requires malloc which is not async signal safe.
C: does it work on a plain-C project (yes, there are still poor souls out there), or is C++ required?
Test setup
All benchmarks will run the following
main.cpp
#include <cstdlib> // strtoul
#include <mystacktrace.h>
void my_func_2(void) {
print_stacktrace(); // line 6
}
void my_func_1(double f) {
(void)f;
my_func_2();
}
void my_func_1(int i) {
(void)i;
my_func_2(); // line 16
}
int main(int argc, char **argv) {
long long unsigned int n;
if (argc > 1) {
n = std::strtoul(argv[1], NULL, 0);
} else {
n = 1;
}
for (long long unsigned int i = 0; i < n; ++i) {
my_func_1(1); // line 27
}
}
This input is designed to test C++ name demangling since my_func_1(int) and my_func_1(float) are necessarily mangled as a way to implement C++ function overload.
We differentiate between the benchmarks by using different -I includes to point to different implementations of print_stacktrace().
Each benchmark is done with a command of form:
time ./stacktrace.out 100000 &>/dev/null
The number of iterations is adjusted for each implementation to produce a total runtime of the order of 1s for that benchmark.
-O0 is used on all tests below unless noted. Stack traces may be irreparably mutilated by certain optimizations. Tail call optimization is a notable example of that: What is tail call optimization? There's nothing we can do about it.
C++23 <stacktrace>
This method was previously mentioned at: https://stackoverflow.com/a/69384663/895245 please consider upvoting that answer.
This is the best solution... it's portable, fast, shows line numbers and demangles C++ symbols. This option will displace every other alternative as soon as it becomes more widely available, with the exception perhaps only of GDB for one-offs without the need or recompilation.
cpp20_stacktrace/mystacktrace.h
#include <iostream>
#include <stacktrace>
void print_stacktrace() {
std::cout << std::stacktrace::current();
}
GCC 12.1.0 from Ubuntu 22.04 does not have support compiled in, so for now I built it from source as per: How to edit and re-build the GCC libstdc++ C++ standard library source? and set --enable-libstdcxx-backtrace=yes, and it worked!
Compile with:
g++ -O0 -ggdb3 -Wall -Wextra -pedantic -std=c++23 -o cpp20_stacktrace.out main.cpp -lstdc++_libbacktrace
Sample output:
0# print_stacktrace() at cpp20_stacktrace/mystacktrace.h:5
1# my_func_2() at /home/ciro/main.cpp:6
2# my_func_1(int) at /home/ciro/main.cpp:16
3# at /home/ciro/main.cpp:27
4# at :0
5# at :0
6# at :0
7#
If we try to use GCC 12.1.0 from Ubuntu 22.04:
sudo apt install g++-12
g++-12 -ggdb3 -O2 -std=c++23 -Wall -Wextra -pedantic -o stacktrace.out stacktrace.cpp -lstdc++_libbacktrace
It fails with:
stacktrace.cpp: In function ‘void my_func_2()’:
stacktrace.cpp:6:23: error: ‘std::stacktrace’ has not been declared
6 | std::cout << std::stacktrace::current();
| ^~~~~~~~~~
Checking build options with:
g++-12 -v
does not show:
--enable-libstdcxx-backtrace=yes
so it wasn't compiled in. Bibliography:
How to use <stacktrace> in GCC trunk?
How can I generate a C++23 stacktrace with GCC 12.1?
It does not fail on the include because the header file:
/usr/include/c++/12
has a feature check:
#if __cplusplus > 202002L && _GLIBCXX_HAVE_STACKTRACE
Boost stacktrace
The library has changed quite a lot around Ubuntu 22.04, so make sure your version matches: Boost stack-trace not showing function names and line numbers
The library is pretty much superseded by the more portable C++23 implementation, but remains a very good option for those that are not at that standard version yet, but already have a "Boost clearance".
Documented at: https://www.boost.org/doc/libs/1_66_0/doc/html/stacktrace/getting_started.html#stacktrace.getting_started.how_to_print_current_call_stack
Tested on Ubuntu 22.04, boost 1.74.0, you should do:
boost_stacktrace/mystacktrace.h
#include <iostream>
#define BOOST_STACKTRACE_LINK
#include <boost/stacktrace.hpp>
void print_stacktrace(void) {
std::cout << boost::stacktrace::stacktrace();
}
On Ubuntu 19.10 boost 1.67.0 to get the line numbers we had to instead:
#include <iostream>
#define BOOST_STACKTRACE_USE_ADDR2LINE
#include <boost/stacktrace.hpp>
void print_stacktrace(void) {
std::cout << boost::stacktrace::stacktrace();
}
which would call out to the addr2line executable and be 1000x slower than the newer Boost version.
The package libboost-stacktrace-dev did not exist at all on Ubuntu 16.04.
The rest of this section considers only the Ubuntu 22.04, boost 1.74 behaviour.
Compile:
sudo apt-get install libboost-stacktrace-dev
g++ -O0 -ggdb3 -Wall -Wextra -pedantic -std=c++11 -o boost_stacktrace.out main.cpp -lboost_stacktrace_backtrace
Sample output:
0# print_stacktrace() at boost_stacktrace/mystacktrace.h:7
1# my_func_2() at /home/ciro/main.cpp:7
2# my_func_1(int) at /home/ciro/main.cpp:17
3# main at /home/ciro/main.cpp:26
4# __libc_start_call_main at ../sysdeps/nptl/libc_start_call_main.h:58
5# __libc_start_main at ../csu/libc-start.c:379
6# _start in ./boost_stacktrace.out
Note that the lines are off by one line. It was suggested in the comments that this is because the following instruction address is being considered.
Boost stacktrace header only
What the BOOST_STACKTRACE_LINK does is to require -lboost_stacktrace_backtrace at link time, so we imagine without that it will just work. This would be a good option for devs who don't have the "Boost clearance" to just add as one offs to debug.
TODO unfortunately it didn't so well for me:
#include <iostream>
#include <boost/stacktrace.hpp>
void print_stacktrace(void) {
std::cout << boost::stacktrace::stacktrace();
}
then:
g++ -O0 -ggdb3 -Wall -Wextra -pedantic -std=c++11 -o boost_stacktrace_header_only.out main.cpp
contains the overly short output:
0# 0x000055FF74AFB601 in ./boost_stacktrace_header_only.out
1# 0x000055FF74AFB66C in ./boost_stacktrace_header_only.out
2# 0x000055FF74AFB69C in ./boost_stacktrace_header_only.out
3# 0x000055FF74AFB6F7 in ./boost_stacktrace_header_only.out
4# 0x00007F0176E7BD90 in /lib/x86_64-linux-gnu/libc.so.6
5# __libc_start_main in /lib/x86_64-linux-gnu/libc.so.6
6# 0x000055FF74AFB4E5 in ./boost_stacktrace_header_only.out
which we can't even use with addr2line. Maybe we have to pass some other define from: https://www.boost.org/doc/libs/1_80_0/doc/html/stacktrace/configuration_and_build.html ?
Tested on Ubuntu 22.04. boost 1.74.
Boost boost::stacktrace::safe_dump_to
This is an interesting alternative to boost::stacktrace::stacktrace as it writes the stack trace in a async signal safe manner to a file, which makes it a good option for automatically dumping stack traces on segfaults which is a super common use case: How to automatically generate a stacktrace when my program crashes
Documented at: https://www.boost.org/doc/libs/1_70_0/doc/html/boost/stacktrace/safe_dump_1_3_38_7_6_2_1_6.html
TODO get it to work. All I see each time is a bunch of random bytes. My attempt:
boost_stacktrace_safe/mystacktrace.h
#include <unistd.h>
#define BOOST_STACKTRACE_LINK
#include <boost/stacktrace.hpp>
void print_stacktrace(void) {
boost::stacktrace::safe_dump_to(0, 1024, STDOUT_FILENO);
}
Sample output:
1[FU1[FU"2[FU}2[FUm1#n10[FU
Changes drastically each time, suggesting it is random memory addresses.
Tested on Ubuntu 22.04, boost 1.74.0.
glibc backtrace
This method is quite portable as it comes with glibc itself. Documented at: https://www.gnu.org/software/libc/manual/html_node/Backtraces.html
Tested on Ubuntu 22.04, glibc 2.35.
glibc_backtrace_symbols_fd/mystacktrace.h
#include <execinfo.h> /* backtrace, backtrace_symbols_fd */
#include <unistd.h> /* STDOUT_FILENO */
void print_stacktrace(void) {
size_t size;
enum Constexpr { MAX_SIZE = 1024 };
void *array[MAX_SIZE];
size = backtrace(array, MAX_SIZE);
backtrace_symbols_fd(array, size, STDOUT_FILENO);
}
Compile with:
g++ -O0 -ggdb3 -Wall -Wextra -pedantic -rdynamic -std=c++11 -o glibc_backtrace_symbols_fd.out main.cpp
Sample output with -rdynamic:
./glibc_backtrace_symbols.out(_Z16print_stacktracev+0x47) [0x556e6a131230]
./glibc_backtrace_symbols.out(_Z9my_func_2v+0xd) [0x556e6a1312d6]
./glibc_backtrace_symbols.out(_Z9my_func_1i+0x14) [0x556e6a131306]
./glibc_backtrace_symbols.out(main+0x58) [0x556e6a131361]
/lib/x86_64-linux-gnu/libc.so.6(+0x29d90) [0x7f175e7bdd90]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x80) [0x7f175e7bde40]
./glibc_backtrace_symbols.out(_start+0x25) [0x556e6a131125]
Sample output without -rdynamic:
./glibc_backtrace_symbols_fd_no_rdynamic.out(+0x11f0)[0x556bd40461f0]
./glibc_backtrace_symbols_fd_no_rdynamic.out(+0x123c)[0x556bd404623c]
./glibc_backtrace_symbols_fd_no_rdynamic.out(+0x126c)[0x556bd404626c]
./glibc_backtrace_symbols_fd_no_rdynamic.out(+0x12c7)[0x556bd40462c7]
/lib/x86_64-linux-gnu/libc.so.6(+0x29d90)[0x7f0da2b70d90]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x80)[0x7f0da2b70e40]
./glibc_backtrace_symbols_fd_no_rdynamic.out(+0x10e5)[0x556bd40460e5]
To get the line numbers without -rdynamic we can use addr2line:
addr2line -C -e glibc_backtrace_symbols_fd_no_rdynamic.out 0x11f0 0x123c 0x126c 0x12c7
addr2line cannot unfortunately handle the function name + offset in function format of when we are not using -rdynamic, e.g. _Z9my_func_2v+0xd.
GDB can however:
gdb -nh -batch -ex 'info line *(_Z9my_func_2v+0xd)' -ex 'info line *(_Z9my_func_1i+0x14)' glibc_backtrace_symbols.out
Line 7 of "main.cpp" starts at address 0x12d6 <_Z9my_func_2v+13> and ends at 0x12d9 <_Z9my_func_1d>.
Line 17 of "main.cpp" starts at address 0x1306 <_Z9my_func_1i+20> and ends at 0x1309 <main(int, char**)>.
A helper to make it more bearable:
addr2lines() (
perl -ne '$m = s/(.*).*\(([^)]*)\).*/gdb -nh -q -batch -ex "info line *\2" \1/;print $_ if $m' | bash
)
Usage:
xsel -b | addr2lines
glibc backtrace_symbols
A version of backtrace_symbols_fd that returns a string rather than printing to a file handle.
glibc_backtrace_symbols/mystacktrace.h
#include <execinfo.h> /* backtrace, backtrace_symbols */
#include <stdio.h> /* printf */
void print_stacktrace(void) {
char **strings;
size_t i, size;
enum Constexpr { MAX_SIZE = 1024 };
void *array[MAX_SIZE];
size = backtrace(array, MAX_SIZE);
strings = backtrace_symbols(array, size);
for (i = 0; i < size; i++)
printf("%s\n", strings[i]);
free(strings);
}
glibc backtrace with C++ demangling hack 1: -export-dynamic + dladdr
I couldn't find a simple way to automatically demangle C++ symbols with glibc backtrace.
https://panthema.net/2008/0901-stacktrace-demangled/
https://gist.github.com/fmela/591333/c64f4eb86037bb237862a8283df70cdfc25f01d3
Adapted from: https://gist.github.com/fmela/591333/c64f4eb86037bb237862a8283df70cdfc25f01d3
This is a "hack" because it requires changing the ELF with -export-dynamic.
glibc_ldl.cpp
#include <dlfcn.h> // for dladdr
#include <cxxabi.h> // for __cxa_demangle
#include <cstdio>
#include <string>
#include <sstream>
#include <iostream>
// This function produces a stack backtrace with demangled function & method names.
std::string backtrace(int skip = 1)
{
void *callstack[128];
const int nMaxFrames = sizeof(callstack) / sizeof(callstack[0]);
char buf[1024];
int nFrames = backtrace(callstack, nMaxFrames);
char **symbols = backtrace_symbols(callstack, nFrames);
std::ostringstream trace_buf;
for (int i = skip; i < nFrames; i++) {
Dl_info info;
if (dladdr(callstack[i], &info)) {
char *demangled = NULL;
int status;
demangled = abi::__cxa_demangle(info.dli_sname, NULL, 0, &status);
std::snprintf(
buf,
sizeof(buf),
"%-3d %*p %s + %zd\n",
i,
(int)(2 + sizeof(void*) * 2),
callstack[i],
status == 0 ? demangled : info.dli_sname,
(char *)callstack[i] - (char *)info.dli_saddr
);
free(demangled);
} else {
std::snprintf(buf, sizeof(buf), "%-3d %*p\n",
i, (int)(2 + sizeof(void*) * 2), callstack[i]);
}
trace_buf << buf;
std::snprintf(buf, sizeof(buf), "%s\n", symbols[i]);
trace_buf << buf;
}
free(symbols);
if (nFrames == nMaxFrames)
trace_buf << "[truncated]\n";
return trace_buf.str();
}
void my_func_2(void) {
std::cout << backtrace() << std::endl;
}
void my_func_1(double f) {
(void)f;
my_func_2();
}
void my_func_1(int i) {
(void)i;
my_func_2();
}
int main() {
my_func_1(1);
my_func_1(2.0);
}
Compile and run:
g++ -fno-pie -ggdb3 -O0 -no-pie -o glibc_ldl.out -std=c++11 -Wall -Wextra \
-pedantic-errors -fpic glibc_ldl.cpp -export-dynamic -ldl
./glibc_ldl.out
output:
1 0x40130a my_func_2() + 41
./glibc_ldl.out(_Z9my_func_2v+0x29) [0x40130a]
2 0x40139e my_func_1(int) + 16
./glibc_ldl.out(_Z9my_func_1i+0x10) [0x40139e]
3 0x4013b3 main + 18
./glibc_ldl.out(main+0x12) [0x4013b3]
4 0x7f7594552b97 __libc_start_main + 231
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7) [0x7f7594552b97]
5 0x400f3a _start + 42
./glibc_ldl.out(_start+0x2a) [0x400f3a]
1 0x40130a my_func_2() + 41
./glibc_ldl.out(_Z9my_func_2v+0x29) [0x40130a]
2 0x40138b my_func_1(double) + 18
./glibc_ldl.out(_Z9my_func_1d+0x12) [0x40138b]
3 0x4013c8 main + 39
./glibc_ldl.out(main+0x27) [0x4013c8]
4 0x7f7594552b97 __libc_start_main + 231
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7) [0x7f7594552b97]
5 0x400f3a _start + 42
./glibc_ldl.out(_start+0x2a) [0x400f3a]
Tested on Ubuntu 18.04.
glibc backtrace with C++ demangling hack 2: parse backtrace output
Shown at: https://panthema.net/2008/0901-stacktrace-demangled/
This is a hack because it requires parsing.
TODO get it to compile and show it here.
GDB scripting
We can also do this with GDB without recompiling by using: How to do an specific action when a certain breakpoint is hit in GDB?
We setup an empty backtrace function for our testing:
gdb/mystacktrace.h
void print_stacktrace(void) {}
and then with:
main.gdb
start
break print_stacktrace
commands
silent
backtrace
printf "\n"
continue
end
continue
we can run:
gdb -nh -batch -x main.gdb --args gdb.out
Sample output:
Temporary breakpoint 1 at 0x11a7: file main.cpp, line 21.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Temporary breakpoint 1, main (argc=1, argv=0x7fffffffc3e8) at main.cpp:21
warning: Source file is more recent than executable.
21 if (argc > 1) {
Breakpoint 2 at 0x555555555151: file gdb/mystacktrace.h, line 1.
#0 print_stacktrace () at gdb/mystacktrace.h:1
#1 0x0000555555555161 in my_func_2 () at main.cpp:6
#2 0x0000555555555191 in my_func_1 (i=1) at main.cpp:16
#3 0x00005555555551ec in main (argc=1, argv=0x7fffffffc3e8) at main.cpp:27
[Inferior 1 (process 165453) exited normally]
The above can be made more usable with the following Bash function:
gdbbt() (
tmpfile=$(mktemp /tmp/gdbbt.XXXXXX)
fn="$1"
shift
printf '%s' "
start
break $fn
commands
silent
backtrace
printf \"\n\"
continue
end
continue
" > "$tmpfile"
gdb -nh -batch -x "$tmpfile" -args "$#"
rm -f "$tmpfile"
)
Usage:
gdbbt print_stacktrace gdb.out 2
I don't know how to make commands with -ex without the temporary file: Problems adding a breakpoint with commands from command line with ex command
Tested in Ubuntu 22.04, GDB 12.0.90.
GDB code injection
TODO this is the dream! It might allow for both compiled-liked speeds, but without the need to recompile! Either:
with compile code + one of the other options, ideally C++23 <stacktrace>: How to call assembly in gdb? Might already be possible. But compile code is mega-quirky so I'm lazy to even try
a built-in dbt command analogous to dprintf dynamic printf: How to do an specific action when a certain breakpoint is hit in GDB?
libunwind
TODO does this have any advantage over glibc backtrace? Very similar output, also requires modifying the build command, but not part of glibc so requires an extra package installation.
Code adapted from: https://eli.thegreenplace.net/2015/programmatic-access-to-the-call-stack-in-c/
main.c
/* This must be on top. */
#define _XOPEN_SOURCE 700
#include <stdio.h>
#include <stdlib.h>
/* Paste this on the file you want to debug. */
#define UNW_LOCAL_ONLY
#include <libunwind.h>
#include <stdio.h>
void print_trace() {
char sym[256];
unw_context_t context;
unw_cursor_t cursor;
unw_getcontext(&context);
unw_init_local(&cursor, &context);
while (unw_step(&cursor) > 0) {
unw_word_t offset, pc;
unw_get_reg(&cursor, UNW_REG_IP, &pc);
if (pc == 0) {
break;
}
printf("0x%lx:", pc);
if (unw_get_proc_name(&cursor, sym, sizeof(sym), &offset) == 0) {
printf(" (%s+0x%lx)\n", sym, offset);
} else {
printf(" -- error: unable to obtain symbol name for this frame\n");
}
}
puts("");
}
void my_func_3(void) {
print_trace();
}
void my_func_2(void) {
my_func_3();
}
void my_func_1(void) {
my_func_3();
}
int main(void) {
my_func_1(); /* line 46 */
my_func_2(); /* line 47 */
return 0;
}
Compile and run:
sudo apt-get install libunwind-dev
gcc -fno-pie -ggdb3 -O3 -no-pie -o main.out -std=c99 \
-Wall -Wextra -pedantic-errors main.c -lunwind
Either #define _XOPEN_SOURCE 700 must be on top, or we must use -std=gnu99:
Is the type `stack_t` no longer defined on linux?
Glibc - error in ucontext.h, but only with -std=c11
Run:
./main.out
Output:
0x4007db: (main+0xb)
0x7f4ff50aa830: (__libc_start_main+0xf0)
0x400819: (_start+0x29)
0x4007e2: (main+0x12)
0x7f4ff50aa830: (__libc_start_main+0xf0)
0x400819: (_start+0x29)
and:
addr2line -e main.out 0x4007db 0x4007e2
gives:
/home/ciro/main.c:34
/home/ciro/main.c:49
With -O0:
0x4009cf: (my_func_3+0xe)
0x4009e7: (my_func_1+0x9)
0x4009f3: (main+0x9)
0x7f7b84ad7830: (__libc_start_main+0xf0)
0x4007d9: (_start+0x29)
0x4009cf: (my_func_3+0xe)
0x4009db: (my_func_2+0x9)
0x4009f8: (main+0xe)
0x7f7b84ad7830: (__libc_start_main+0xf0)
0x4007d9: (_start+0x29)
and:
addr2line -e main.out 0x4009f3 0x4009f8
gives:
/home/ciro/main.c:47
/home/ciro/main.c:48
Tested on Ubuntu 16.04, GCC 6.4.0, libunwind 1.1.
libunwind with C++ name demangling
Code adapted from: https://eli.thegreenplace.net/2015/programmatic-access-to-the-call-stack-in-c/
unwind.cpp
#define UNW_LOCAL_ONLY
#include <cxxabi.h>
#include <libunwind.h>
#include <cstdio>
#include <cstdlib>
#include <iostream>
void backtrace() {
unw_cursor_t cursor;
unw_context_t context;
// Initialize cursor to current frame for local unwinding.
unw_getcontext(&context);
unw_init_local(&cursor, &context);
// Unwind frames one by one, going up the frame stack.
while (unw_step(&cursor) > 0) {
unw_word_t offset, pc;
unw_get_reg(&cursor, UNW_REG_IP, &pc);
if (pc == 0) {
break;
}
std::printf("0x%lx:", pc);
char sym[256];
if (unw_get_proc_name(&cursor, sym, sizeof(sym), &offset) == 0) {
char* nameptr = sym;
int status;
char* demangled = abi::__cxa_demangle(sym, nullptr, nullptr, &status);
if (status == 0) {
nameptr = demangled;
}
std::printf(" (%s+0x%lx)\n", nameptr, offset);
std::free(demangled);
} else {
std::printf(" -- error: unable to obtain symbol name for this frame\n");
}
}
}
void my_func_2(void) {
backtrace();
std::cout << std::endl; // line 43
}
void my_func_1(double f) {
(void)f;
my_func_2();
}
void my_func_1(int i) {
(void)i;
my_func_2();
} // line 54
int main() {
my_func_1(1);
my_func_1(2.0);
}
Compile and run:
sudo apt-get install libunwind-dev
g++ -fno-pie -ggdb3 -O0 -no-pie -o unwind.out -std=c++11 \
-Wall -Wextra -pedantic-errors unwind.cpp -lunwind -pthread
./unwind.out
Output:
0x400c80: (my_func_2()+0x9)
0x400cb7: (my_func_1(int)+0x10)
0x400ccc: (main+0x12)
0x7f4c68926b97: (__libc_start_main+0xe7)
0x400a3a: (_start+0x2a)
0x400c80: (my_func_2()+0x9)
0x400ca4: (my_func_1(double)+0x12)
0x400ce1: (main+0x27)
0x7f4c68926b97: (__libc_start_main+0xe7)
0x400a3a: (_start+0x2a)
and then we can find the lines of my_func_2 and my_func_1(int) with:
addr2line -e unwind.out 0x400c80 0x400cb7
which gives:
/home/ciro/test/unwind.cpp:43
/home/ciro/test/unwind.cpp:54
TODO: why are the lines off by one?
Tested on Ubuntu 18.04, GCC 7.4.0, libunwind 1.2.1.
Linux kernel
How to print the current thread stack trace inside the Linux kernel?
libdwfl
This was originally mentioned at: https://stackoverflow.com/a/60713161/895245 and it might be the best method, but I have to benchmark a bit more, but please go upvote that answer.
TODO: I tried to minimize the code in that answer, which was working, to a single function, but it is segfaulting, let me know if anyone can find why.
dwfl.cpp: answer reached 30k chars and this was the easiest cut: https://gist.github.com/cirosantilli/f1dd3ee5d324b9d24e40f855723544ac
Compile and run:
sudo apt install libdw-dev libunwind-dev
g++ -fno-pie -ggdb3 -O0 -no-pie -o dwfl.out -std=c++11 -Wall -Wextra -pedantic-errors dwfl.cpp -ldw -lunwind
./dwfl.out
We also need libunwind as that makes results more correct. If you do without it, it runs, but you will see that some of the lines are a bit wrong.
Output:
0: 0x402b72 stacktrace[abi:cxx11]() at /home/ciro/test/dwfl.cpp:65
1: 0x402cda my_func_2() at /home/ciro/test/dwfl.cpp:100
2: 0x402d76 my_func_1(int) at /home/ciro/test/dwfl.cpp:111
3: 0x402dd1 main at /home/ciro/test/dwfl.cpp:122
4: 0x7ff227ea0d8f __libc_start_call_main at ../sysdeps/nptl/libc_start_call_main.h:58
5: 0x7ff227ea0e3f __libc_start_main##GLIBC_2.34 at ../csu/libc-start.c:392
6: 0x402534 _start at ../csu/libc-start.c:-1
0: 0x402b72 stacktrace[abi:cxx11]() at /home/ciro/test/dwfl.cpp:65
1: 0x402cda my_func_2() at /home/ciro/test/dwfl.cpp:100
2: 0x402d5f my_func_1(double) at /home/ciro/test/dwfl.cpp:106
3: 0x402de2 main at /home/ciro/test/dwfl.cpp:123
4: 0x7ff227ea0d8f __libc_start_call_main at ../sysdeps/nptl/libc_start_call_main.h:58
5: 0x7ff227ea0e3f __libc_start_main##GLIBC_2.34 at ../csu/libc-start.c:392
6: 0x402534 _start at ../csu/libc-start.c:-1
Benchmark run:
g++ -fno-pie -ggdb3 -O3 -no-pie -o dwfl.out -std=c++11 -Wall -Wextra -pedantic-errors dwfl.cpp -ldw
time ./dwfl.out 1000 >/dev/null
Output:
real 0m3.751s
user 0m2.822s
sys 0m0.928s
So we see that this method is 10x faster than Boost's stacktrace, and might therefore be applicable to more use cases.
Tested in Ubuntu 22.04 amd64, libdw-dev 0.186, libunwind 1.3.2.
libbacktrace
https://github.com/ianlancetaylor/libbacktrace
Considering the harcore library author, it is worth trying this out, maybe it is The One. TODO check it out.
A C library that may be linked into a C/C++ program to produce symbolic backtraces
As of October 2020, libbacktrace supports ELF, PE/COFF, Mach-O, and XCOFF executables with DWARF debugging information. In other words, it supports GNU/Linux, *BSD, macOS, Windows, and AIX. The library is written to make it straightforward to add support for other object file and debugging formats.
The library relies on the C++ unwind API defined at https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html This API is provided by GCC and clang.
See also
How can one grab a stack trace in C?
How to make backtrace()/backtrace_symbols() print the function names?
Is there a portable/standard-compliant way to get filenames and linenumbers in a stack trace?
Best way to invoke gdb from inside program to print its stacktrace?
automatic stack trace on failure:
on C++ exception: C++ display stack trace on exception
generic: How to automatically generate a stacktrace when my program crashes
For a linux-only solution you can use backtrace(3) that simply returns an array of void * (in fact each of these point to the return address from the corresponding stack frame). To translate these to something of use, there's backtrace_symbols(3).
Pay attention to the notes section in backtrace(3):
The symbol names may be unavailable
without the use of special linker
options.
For systems using the GNU linker, it is necessary to use the
-rdynamic linker
option. Note that names of "static" functions are not exposed,
and won't be
available in the backtrace.
In C++23, there will be <stacktrace>, and then you can do:
#include <stacktrace>
/* ... */
std::cout << std::stacktrace::current();
Further details:
• https://en.cppreference.com/w/cpp/header/stacktrace
• https://en.cppreference.com/w/cpp/utility/basic_stacktrace/operator_ltlt
Is there any way to dump the call stack in a running process in C or C++ every time a certain function is called?
You can use a macro function instead of return statement in the specific function.
For example, instead of using return,
int foo(...)
{
if (error happened)
return -1;
... do something ...
return 0
}
You can use a macro function.
#include "c-callstack.h"
int foo(...)
{
if (error happened)
NL_RETURN(-1);
... do something ...
NL_RETURN(0);
}
Whenever an error happens in a function, you will see Java-style call stack as shown below.
Error(code:-1) at : so_topless_ranking_server (sample.c:23)
Error(code:-1) at : nanolat_database (sample.c:31)
Error(code:-1) at : nanolat_message_queue (sample.c:39)
Error(code:-1) at : main (sample.c:47)
Full source code is available here.
c-callstack at https://github.com/Nanolat
Linux specific, TLDR:
backtrace in glibc produces accurate stacktraces only when -lunwind is linked (undocumented platform-specific feature).
To output function name, source file and line number use #include <elfutils/libdwfl.h> (this library is documented only in its header file). backtrace_symbols and backtrace_symbolsd_fd are least informative.
On modern Linux your can get the stacktrace addresses using function backtrace. The undocumented way to make backtrace produce more accurate addresses on popular platforms is to link with -lunwind (libunwind-dev on Ubuntu 18.04) (see the example output below). backtrace uses function _Unwind_Backtrace and by default the latter comes from libgcc_s.so.1 and that implementation is most portable. When -lunwind is linked it provides a more accurate version of _Unwind_Backtrace but this library is less portable (see supported architectures in libunwind/src).
Unfortunately, the companion backtrace_symbolsd and backtrace_symbols_fd functions have not been able to resolve the stacktrace addresses to function names with source file name and line number for probably a decade now (see the example output below).
However, there is another method to resolve addresses to symbols and it produces the most useful traces with function name, source file and line number. The method is to #include <elfutils/libdwfl.h>and link with -ldw (libdw-dev on Ubuntu 18.04).
Working C++ example (test.cc):
#include <stdexcept>
#include <iostream>
#include <cassert>
#include <cstdlib>
#include <string>
#include <boost/core/demangle.hpp>
#include <execinfo.h>
#include <elfutils/libdwfl.h>
struct DebugInfoSession {
Dwfl_Callbacks callbacks = {};
char* debuginfo_path = nullptr;
Dwfl* dwfl = nullptr;
DebugInfoSession() {
callbacks.find_elf = dwfl_linux_proc_find_elf;
callbacks.find_debuginfo = dwfl_standard_find_debuginfo;
callbacks.debuginfo_path = &debuginfo_path;
dwfl = dwfl_begin(&callbacks);
assert(dwfl);
int r;
r = dwfl_linux_proc_report(dwfl, getpid());
assert(!r);
r = dwfl_report_end(dwfl, nullptr, nullptr);
assert(!r);
static_cast<void>(r);
}
~DebugInfoSession() {
dwfl_end(dwfl);
}
DebugInfoSession(DebugInfoSession const&) = delete;
DebugInfoSession& operator=(DebugInfoSession const&) = delete;
};
struct DebugInfo {
void* ip;
std::string function;
char const* file;
int line;
DebugInfo(DebugInfoSession const& dis, void* ip)
: ip(ip)
, file()
, line(-1)
{
// Get function name.
uintptr_t ip2 = reinterpret_cast<uintptr_t>(ip);
Dwfl_Module* module = dwfl_addrmodule(dis.dwfl, ip2);
char const* name = dwfl_module_addrname(module, ip2);
function = name ? boost::core::demangle(name) : "<unknown>";
// Get source filename and line number.
if(Dwfl_Line* dwfl_line = dwfl_module_getsrc(module, ip2)) {
Dwarf_Addr addr;
file = dwfl_lineinfo(dwfl_line, &addr, &line, nullptr, nullptr, nullptr);
}
}
};
std::ostream& operator<<(std::ostream& s, DebugInfo const& di) {
s << di.ip << ' ' << di.function;
if(di.file)
s << " at " << di.file << ':' << di.line;
return s;
}
void terminate_with_stacktrace() {
void* stack[512];
int stack_size = ::backtrace(stack, sizeof stack / sizeof *stack);
// Print the exception info, if any.
if(auto ex = std::current_exception()) {
try {
std::rethrow_exception(ex);
}
catch(std::exception& e) {
std::cerr << "Fatal exception " << boost::core::demangle(typeid(e).name()) << ": " << e.what() << ".\n";
}
catch(...) {
std::cerr << "Fatal unknown exception.\n";
}
}
DebugInfoSession dis;
std::cerr << "Stacktrace of " << stack_size << " frames:\n";
for(int i = 0; i < stack_size; ++i) {
std::cerr << i << ": " << DebugInfo(dis, stack[i]) << '\n';
}
std::cerr.flush();
std::_Exit(EXIT_FAILURE);
}
int main() {
std::set_terminate(terminate_with_stacktrace);
throw std::runtime_error("test exception");
}
Compiled on Ubuntu 18.04.4 LTS with gcc-8.3:
g++ -o test.o -c -m{arch,tune}=native -std=gnu++17 -W{all,extra,error} -g -Og -fstack-protector-all test.cc
g++ -o test -g test.o -ldw -lunwind
Outputs:
Fatal exception std::runtime_error: test exception.
Stacktrace of 7 frames:
0: 0x55f3837c1a8c terminate_with_stacktrace() at /home/max/src/test/test.cc:76
1: 0x7fbc1c845ae5 <unknown>
2: 0x7fbc1c845b20 std::terminate()
3: 0x7fbc1c845d53 __cxa_throw
4: 0x55f3837c1a43 main at /home/max/src/test/test.cc:103
5: 0x7fbc1c3e3b96 __libc_start_main at ../csu/libc-start.c:310
6: 0x55f3837c17e9 _start
When no -lunwind is linked, it produces a less accurate stacktrace:
0: 0x5591dd9d1a4d terminate_with_stacktrace() at /home/max/src/test/test.cc:76
1: 0x7f3c18ad6ae6 <unknown>
2: 0x7f3c18ad6b21 <unknown>
3: 0x7f3c18ad6d54 <unknown>
4: 0x5591dd9d1a04 main at /home/max/src/test/test.cc:103
5: 0x7f3c1845cb97 __libc_start_main at ../csu/libc-start.c:344
6: 0x5591dd9d17aa _start
For comparison, backtrace_symbols_fd output for the same stacktrace is least informative:
/home/max/src/test/debug/gcc/test(+0x192f)[0x5601c5a2092f]
/usr/lib/x86_64-linux-gnu/libstdc++.so.6(+0x92ae5)[0x7f95184f5ae5]
/usr/lib/x86_64-linux-gnu/libstdc++.so.6(_ZSt9terminatev+0x10)[0x7f95184f5b20]
/usr/lib/x86_64-linux-gnu/libstdc++.so.6(__cxa_throw+0x43)[0x7f95184f5d53]
/home/max/src/test/debug/gcc/test(+0x1ae7)[0x5601c5a20ae7]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe6)[0x7f9518093b96]
/home/max/src/test/debug/gcc/test(+0x1849)[0x5601c5a20849]
In a production version (as well as C language version) you may like to make this code extra robust by replacing boost::core::demangle, std::string and std::cout with their underlying calls.
You can also override __cxa_throw to capture the stacktrace when an exception is thrown and print it when the exception is caught. By the time it enters catch block the stack has been unwound, so it is too late to call backtrace, and this is why the stack must be captured on throw which is implemented by function __cxa_throw. Note that in a multi-threaded program __cxa_throw can be called simultaneously by multiple threads, so that if it captures the stacktrace into a global array that must be thread_local.
You can also make the stack trace printing function async-signal safe, so that you can invoke it directly from your SIGSEGV, SIGBUS signal handlers (which should use their own stacks for robustness). Obtaining function name, source file and line number using libdwfl from a signal handler may fail because it is not async-signal safe or if the address space of the process has been substantially corrupted, but in practice it succeeds 99% of the time (I haven't seen it fail).
To summarize, a complete production-ready library for automatic stacktrace output should:
Capture the stacktrace on throw into thread-specific storage.
Automatically print the stacktrace on unhandled exceptions.
Print the stacktrace in async-signal-safe manner.
Provide a robust signal handler function which uses its own stack that prints the stacktrace in a async-signal-safe manner. The user can install this function as a signal handler for SIGSEGV, SIGBUS, SIGFPE, etc..
The signal handler may as well print the values of all CPU registers at the point of the fault from ucontext_t signal function argument (may be excluding vector registers), a-la Linux kernel oops log messages.
Another answer to an old thread.
When I need to do this, I usually just use system() and pstack
So something like this:
#include <sys/types.h>
#include <unistd.h>
#include <string>
#include <sstream>
#include <cstdlib>
void f()
{
pid_t myPid = getpid();
std::string pstackCommand = "pstack ";
std::stringstream ss;
ss << myPid;
pstackCommand += ss.str();
system(pstackCommand.c_str());
}
void g()
{
f();
}
void h()
{
g();
}
int main()
{
h();
}
This outputs
#0 0x00002aaaab62d61e in waitpid () from /lib64/libc.so.6
#1 0x00002aaaab5bf609 in do_system () from /lib64/libc.so.6
#2 0x0000000000400c3c in f() ()
#3 0x0000000000400cc5 in g() ()
#4 0x0000000000400cd1 in h() ()
#5 0x0000000000400cdd in main ()
This should work on Linux, FreeBSD and Solaris. I don't think that macOS has pstack or a simple equivalent, but this thread seems to have an alternative.
If you are using C, then you will need to use C string functions.
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
void f()
{
pid_t myPid = getpid();
/*
length of command 7 for 'pstack ', 7 for the PID, 1 for nul
*/
char pstackCommand[7+7+1];
sprintf(pstackCommand, "pstack %d", (int)myPid);
system(pstackCommand);
}
I've used 7 for the max number of digits in the PID, based on this post.
There is no standardized way to do that. For windows the functionality is provided in the DbgHelp library
You can use the Boost libraries to print the current callstack.
#include <boost/stacktrace.hpp>
// ... somewhere inside the `bar(int)` function that is called recursively:
std::cout << boost::stacktrace::stacktrace();
Man here: https://www.boost.org/doc/libs/1_65_1/doc/html/stacktrace.html
I know this thread is old, but I think it can be useful for other people. If you are using gcc, you can use its instrument features (-finstrument-functions option) to log any function call (entry and exit). Have a look at this for more information: http://hacktalks.blogspot.fr/2013/08/gcc-instrument-functions.html
You can thus for instance push and pop every calls into a stack, and when you want to print it, you just look at what you have in your stack.
I've tested it, it works perfectly and is very handy
UPDATE: you can also find information about the -finstrument-functions compile option in the GCC doc concerning the Instrumentation options: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html
You can implement the functionality yourself:
Use a global (string)stack and at start of each function push the function name and such other values (eg parameters) onto this stack; at exit of function pop it again.
Write a function that will printout the stack content when it is called, and use this in the function where you want to see the callstack.
This may sound like a lot of work but is quite useful.
Of course the next question is: will this be enough ?
The main disadvantage of stack-traces is that why you have the precise function being called you do not have anything else, like the value of its arguments, which is very useful for debugging.
If you have access to gcc and gdb, I would suggest using assert to check for a specific condition, and produce a memory dump if it is not met. Of course this means the process will stop, but you'll have a full fledged report instead of a mere stack-trace.
If you wish for a less obtrusive way, you can always use logging. There are very efficient logging facilities out there, like Pantheios for example. Which once again could give you a much more accurate image of what is going on.
You can use Poppy for this. It is normally used to gather the stack trace during a crash but it can also output it for a running program as well.
Now here's the good part: it can output the actual parameter values for each function on the stack, and even local variables, loop counters, etc.
You can use the GNU profiler. It shows the call-graph as well! the command is gprof and you need to compile your code with some option.
Is there any way to dump the call stack in a running process in C or C++ every time a certain function is called?
No there is not, although platform-dependent solutions might exist.
I am using the standard __wrap_function and __real_function to intercept function calls with -Wl,--wrap=function. This works successfully for most functions like malloc, fopen, etc. However, I am unable to wrap these two functions:
int connect(int, const struct sockaddr*, socklen_t)
int stat(const char*, struct stat*)
With these functions, the linker complains with undefined reference to __real_connect and __real_stat.
Is there any particular reason for this? (Note: I can also wrap socket functions for example)
It is likely you forgot to add -Wl,--wrap=connect and -Wl,--wrap=stat to your link line.
This works for me:
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <unistd.h>
int __wrap_connect (int s, const struct sockaddr *addr, socklen_t len)
{
puts(__func__);
return __real_connect(s, addr, len);
}
int __wrap_stat (const char *path, struct stat *buf)
{
puts(__func__);
return __real_stat(path, buf);
}
int main(void) {
connect(0, NULL, 0);
stat("/", 0);
return 0;
}
When compiled on my system.
$ uname -s -r
Linux 2.6.32-696.16.1.el6.x86_64
$ gcc --version | grep gcc
gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-18)
$ gcc c.c -Wl,--wrap=connect -Wl,--wrap=stat
$
However, when leaving off -Wl,--wrap=stat, for example, I get:
$ gcc c.c -Wl,--wrap=connect
/tmp/cchVzvsE.o: In function `__wrap_stat':
c.c:(.text+0x65): undefined reference to `__real_stat'
collect2: ld returned 1 exit status
$
It seems like the error was caused due to cmake issues. Clearing the cmake cache and running cmake . followed by make all resolved it.
I am currently working on developing over-the-air programming support on sky motes. Attached are the files that I have so far. I am basically trying to use the sky-shell-exec example to load my modified test-deluge.ce file onto the mote. I then try to run the test-deluge file using the shell 'exec' command as done in the sky-shell-exec example.
The final goal is to load both the test-deluge.ce and hello-world.ce compiled files onto the mote and then be able to 'exec' my test-deluge.ce file which would then find the stored hello-world.ce file and do a deluge_disseminate on it.
The progression of command I am running are as follows:
1) sudo make TARGET=sky clean CLEAN=symbols.?
2) sudo make sky-shell-exec.sky TARGET=sky
3) sudo make sky-shell-exec.sky CORE=sky-shell-exec.sky TARGET=sky
4) sudo make sky-shell-exec.upload CORE=sky-shell-exec.sky
5) sudo make compile-test-deluge-executable
6) sudo make upload-test-deluge-executable
7) sudo make login
8) ls (to see that the file made it)
9) exec test-deluge.ce
At this point I get a 'Symbol not found: deluge_disseminate' error
I believe the error is in the 'CORE=...' part of the make (in step 2 above). I have inspected the symbols.c file that is filled out in step 2 of the above and indeed there is no symbol for deluge_disseminate or any of the deluge commands for that matter that I recall.
For experimentation I tried the following:
sudo make test-deluge.sky TARGET=sky
sudo make test-deluge.sky CORE=test-deluge.sky TARGET=sky
and I find that the symbols for deluge are there, but I can't proceed to properly make sky-shell-exec file since doing so erases the symbols table and writes a new one.
I feel like there must be a simple fix to this as I can run hello-world from the sky-shell-exec example directory after following the above steps (1-9).
Does anyone have an idea of how to go about this?
NOTE: There may be a bug in my test-deluge.c where I try to open 'hello-world.sky' instead of 'hello-world.ce'...I wasn't really sure which one. I haven't been able to test this yet because of the missing symbol issue explained above, but if anyone would be willing to shed light on this issue as well I would be very appreciative.
Thanks
MAKEFILE
CONTIKI = ../..
ifndef TARGET
TARGET=sky
endif
APPS = deluge serial-shell
all: blink sky-collect #rt-leds test-button test-cfs tcprudolph0
#all: $(CONTIKI_PROJECT)
%.tgz: %.ihex
mkdir $(basename $<) ; \
mv $< $(basename $<) ; \
echo $(basename $<)/$(basename $<).ihex 600 > $(basename $<)/runfile ; \
tar czf $# $(basename $<)
%.class: %.java
javac $(basename $<).java
viewrssi: ViewRSSI.class
make login | java ViewRSSI
include $(CONTIKI)/Makefile.include
%.shell-upload: %.ce
(echo; sleep 4; echo "~K"; sleep 4; \
echo "dec64 | write $*.ce | null"; sleep 4; \
../../tools/base64-encode < $<; sleep 4; \
echo ""; echo "~K"; echo "read $*.ce | size"; sleep 4) | make login
.PHONY: compile-test-deluge-executable upload-test-deluge-executable compile-hello-world-executable upload-test-deluge-executable
compile-hello-world-executable: hello-world.ce
echo Compiled Contiki executable: $<
upload-hello-world-executable: hello-world.shell-upload
echo Uploaded Contiki executable: $<
compile-test-deluge-executable: test-deluge.ce
echo Compiled Contiki executable: $<
upload-test-deluge-executable: test-deluge.shell-upload
echo Uploaded Contiki executable: $<
sky-shell-exec.c
#include "contiki.h"
#include "shell.h"
#include "serial-shell.h"
#include "deluge.h"
#include "dev/watchdog.h"
#include "net/rime.h"
#include "dev/cc2420.h"
#include "dev/leds.h"
#include "dev/light.h"
#include "dev/sht11.h"
#include "dev/battery-sensor.h"
#include "lib/checkpoint.h"
#include "net/rime/timesynch.h"
#include <stdio.h>
#include <string.h>
int (*keep_1)(void) = deluge_disseminate;
int (*keep_2)(void) = node_id_burn;
/*---------------------------------------------------------------------------*/
PROCESS(sky_shell_process, "Sky Contiki shell");
AUTOSTART_PROCESSES(&sky_shell_process);
/*---------------------------------------------------------------------------*/
PROCESS_THREAD(sky_shell_process, ev, data)
{
PROCESS_BEGIN();
serial_shell_init();
/*shell_blink_init();*/
shell_file_init();
shell_coffee_init();
/*shell_ps_init();*/
/*shell_reboot_init();*/
/*shell_rime_init();*/
/*shell_rime_netcmd_init();*/
/*shell_rime_ping_init();*/
/*shell_rime_debug_init();*/
/*shell_rime_sniff_init();*/
/*shell_sky_init();*/
shell_text_init();
/*shell_time_init();*/
/* shell_checkpoint_init();*/
shell_exec_init();
shell_base64_init();
PROCESS_END();
}
/*---------------------------------------------------------------------------*/
test-deluge.c
#include "contiki.h"
#include "cfs/cfs.h"
#include "deluge.h"
#include "sys/node-id.h"
#include "loader/elfloader.h"
#include <stdio.h>
#include <string.h>
#ifndef SINK_ID
#define SINK_ID 1
#endif
#ifndef FILE_SIZE
#define FILE_SIZE 1000
#endif
PROCESS(deluge_test_process, "Deluge test process");
AUTOSTART_PROCESSES(&deluge_test_process);
/*---------------------------------------------------------------------------*/
PROCESS_THREAD(deluge_test_process, ev, data)
{
static struct etimer et;
node_id_burn(2);
PROCESS_BEGIN();
if(node_id == SINK_ID) {
printf("Sink node: trying to transmit file.\n");
} else {
printf("Non-sink node: trying to recieve file.\n");
}
cfs_remove("hello-world.sky");
int fd = cfs_open("hello-world.sky", CFS_WRITE | CFS_READ);
if(fd < 0) {
process_exit(NULL);
}
#if 0
if(cfs_seek(fd, FILE_SIZE, CFS_SEEK_SET) != FILE_SIZE) {
printf("failed to seek to the end\n");
}
#endif
deluge_disseminate("hello-world.sky", node_id == SINK_ID);
cfs_close(fd);
etimer_set(&et, CLOCK_SECOND * 5);
PROCESS_WAIT_EVENT_UNTIL(etimer_expired(&et));
if(node_id != SINK_ID) {
fd = cfs_open("hello-world.sky", CFS_READ);
if(fd < 0) {
printf("failed to open the test file\n");
} else {
printf("Start dynamic loading\n");
int ret = elfloader_load(fd);
printf("%d\n", ret);
cfs_close(fd);
int i;
switch(ret) {
case ELFLOADER_OK:
for(i=0; elfloader_autostart_processes[i] != NULL; i++) {
printf("exec: starting process %s. \n",
elfloader_autostart_processes[i]->name);
}
autostart_start(elfloader_autostart_processes);
break;
default:
printf("Unkown return code from ELF loader (internal bug)\n");
break;
}
}
}
etimer_reset(&et);
PROCESS_END();
}
/*---------------------------------------------------------------------------*/
hello-world.c
#include "contiki.h"
#include <stdio.h> /* For printf() */
/*---------------------------------------------------------------------------*/
PROCESS(hello_world_process, "Hello world process");
AUTOSTART_PROCESSES(&hello_world_process);
/*---------------------------------------------------------------------------*/
PROCESS_THREAD(hello_world_process, ev, data)
{
PROCESS_BEGIN();
printf("Hello, world\n");
PROCESS_END();
}
/*---------------------------------------------------------------------------*/
So with great help from the contiki community I was able to gather the following solution:
"Hi,
The problem is that the build system of Contiki tries to "act smart"
and excludes symbols the application apparently does not need. So in
this case the deluge_disseminate function code is optimized away from
sky-shell-exec executable. Obviously, this conflicts with the basic
intuitions that the programmer has in case of over-the-air
programming.
To work around this issue, add a reference to deluge_disseminate in
sky-shell-exec code. For example, add this line (at global scope):
int (*keep)(void) = deluge_disseminate;
You can also try to tweak GCC linker options or use a custom linker script."
Using the same trick for node_id_burn as well, test-deluge.c runs.
The corrections have been made to the above code.
Hopefully this helps anyone else out there who may be struggling with OTA code in Contiki.
I'm trying to get the exit code of a subprocess. On Linux and FreeBSD I can go like so:
[0] [ishpeck#kiyoshi /tmp]$ uname
FreeBSD
[0] [ishpeck#kiyoshi /tmp]$ cat tinker.c
#include <stdio.h>
#include <sys/wait.h>
int main(void)
{
FILE *proc = popen("ls", "r");
printf("Exit code: %d\n", WEXITSTATUS(pclose(proc)));
return 0;
}
[0] [ishpeck#kiyoshi /tmp]$ gcc tinker.c -o tinker
[0] [ishpeck#kiyoshi /tmp]$ ./tinker
Exit code: 0
[0] [ishpeck#kiyoshi /tmp]$ grep WEXITSTATUS /usr/include/sys/wait.h
#define WEXITSTATUS(x) (_W_INT(x) >> 8)
However, on OpenBSD, I get complaints from the compiler...
[0] [ishpeck#ishberk-00 /tmp]$ uname
OpenBSD
[0] [ishpeck#ishberk-00 /tmp]$ cat tinker.c
#include <stdio.h>
#include <sys/wait.h>
int main(void)
{
FILE *proc = popen("ls", "r");
printf("Exit code: %d\n", WEXITSTATUS(pclose(proc)));
return 0;
}
[0] [ishpeck#ishberk-00 /tmp]$ gcc tinker.c -o tinker
tinker.c: In function 'main':
tinker.c:7: error: lvalue required as unary '&' operand
[1] [ishpeck#ishberk-00 /tmp]$ grep WEXITSTATUS /usr/include/sys/wait.h
#define WEXITSTATUS(x) (int)(((unsigned)_W_INT(x) >> 8) & 0xff)
I don't really care how it's done, I just need the exit code.
This leads me to believe that I would also have this problem on Mac:
http://web.archiveorange.com/archive/v/8XiUWJBLMIKYSCRJnZK5#F4GgyRGRAgSCEG1
Is there a more portable way to use the WEXITSTATUS macro? Or is there a more portable alternative?
OpenBSD's implementation of WEXITSTATUS uses the address-of operator (unary &) on its argument, effectively requiring that its argument have storage. You are calling it with the return value of a function, which doesn't have storage, so the compiler complains.
It is unclear whether OpenBSD's WEXITSTATUS is POSIX-compliant, but the problem can be easily worked around by assigning the return value of pclose() to a variable:
int status = pclose(proc);
printf("Exit code: %d\n", WEXITSTATUS(status));
As a detail that could go unnoticed for some people arriving here, BSD object code needs the library:
#include <sys/wait.h>
I was too compiling to Linux and BSD, and WEXITSTATUS worked OK without the need for that library (I don't know why) when compiling to Linux (using gcc), but failed when compiling to BSD (using clang).
If your application died or was otherwise killed, the return status is bogus. You need to check the status to see if the exit value is even valid. See the man page for waitpid.
if(WIFEXITED(status))
{
use WEXITSTATUS(status);
} else if (WIFSIGNALED(status)) {
use WTERMSIG(status);
} else {
oh oh
}
This is more focused than my previous Valgrind question; I am trying to narrow down write and read errors when parsing command-line options:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/utsname.h>
#include <sys/stat.h>
#include <string.h>
#include <locale.h>
#include <bzlib.h>
#include <zlib.h>
#include "starch.h"
#define BUFMAXLEN 1024
int main(int argc, char **argv) {
if (parseCommandLineInputs( &argc, &argv ) != 0)
exit(EXIT_FAILURE);
return 0;
}
int parseCommandLineInputs(int *argc, char ***argv) {
pid_t pid;
struct utsname uts;
char uniqTag[BUFMAXLEN];
if ((*argc == 1) || (*argc > 4)) {
printUsage();
return -1;
}
if ((pid = getpid()) < 0) {
fprintf(stderr, "\n\t[starch] - Error: Could not obtain process ID\n\n");
return -1;
}
uname( &uts );
sprintf(uniqTag, "pid%d.%s", pid, uts.nodename);
switch (*argc) {
case 2: {
if (strcmp(*argv[1], "-") != 0) {
if (fileExists(*argv[1]) != 0) { /* standard input */
...
}
return 0;
}
int fileExists(char *fn) {
struct stat buf;
int i = stat (fn, &buf);
if (i == 0)
return 0;
return -1;
}
void printUsage() {
fprintf(stderr, "my usage statement\n\n");
}
My makefile is as follows:
CC = gcc
CFLAGS = -D_FILE_OFFSET_BITS=64 -D_LARGEFILE64_SOURCE=1 -DUSE_ZLIB -O3 -Wformat -Wall -pedantic -std=gnu99 -g
BIN = ../bin
all: starch
rm -rf *~
starch: starch.o
mkdir -p $(BIN) && $(CC) ${CFLAGS} starch.o -lbz2 -lz -o ${BIN}/starch
rm -rf *~
clean:
rm -rf *.o *~ ${BIN}/starch
I get the following errors when I run with valgrind:
$ valgrind --tool=memcheck --leak-check=yes --show-reachable=yes --num-callers=20 --track-fds=yes -v ../bin/starch
...
==2675== 1 errors in context 1 of 2:
==2675== Invalid read of size 8
==2675== at 0x3AB4262243: fwrite (in /lib64/libc-2.5.so)
==2675== Address 0x7fedffd68 is on thread 1's stack
==2675==
==2675==
==2675== 1 errors in context 2 of 2:
==2675== Invalid write of size 8
==2675== at 0x401AA6: parseCommandLineInputs (starch.c:217)
==2675== by 0x7FF0000AF: ???
==2675== by 0x401DFA: main (starch.c:46)
==2675== Address 0x7fedffd68 is on thread 1's stack
The first error is not telling me anything I can use, since I am not using fwrite() anywhere.
The second error is tripped up on the fprintf statement in printUsage().
Line 46 is the following line:
if (parseCommandLineInputs( &argc, &argv ) != 0)
Line 217 is the following line:
fprintf(stderr, "my usage statement\n\n");
What is wrong with my application that explains why these errors appear?
Two things that pop up to me right away:
*argv[1] is NOT the same as (*argv)[1] which is what you probably mean. Array subscripting has precedence over pointer dereferencing. This results in an invalid pointer. As many experienced programmers will tell you: "Don't try to remember the precedence of operators - if in doubt use parentheses, if not just use them anyway".
-O3 in the compiler flags is a big fat NO-NO when debugging. The compiler will mangle your code so much that it can make your life impossible. Variables can disappear completely and functions can go mysteriously away as they get inlined. If your code compiles, links and runs with -O0 (IIRC some code containing inline assembly needs -O1 with some (all?) GCC versions) use it, otherwise use -O1 at most.
There is too much missing so it is not easy to tell what is going on. I suppose that pid is pid_t?
The only thing that I then see is this one:
sprintf(uniqTag, "pid%d.%s", pid, uts.nodename);
pid_t is not necessarily an int so sprintf might be on the wrong track when parsing its arguments and messup your stack. But gcc should have have told you if you compile with -Wall, which I suppose.
Try compiling with a different compiler, clang e.g.