Mark Hahn wrote:
It's highly dependant to implement but I should imagine most people who
need backtraces use a debugger,
suppose your program is running on a hundred nodes for a week before you
hit the event you want the backtrace for...
yes, debugger+coredump can be used, but for obvious reasons,
we normally recommend users _not_ have them enabled.
Sorry to start a flame war....
Make sure that your code generates the exact same answer with
debug/backtrace enabled and disabled, then you add user-level
checkpointing so that you can restart where you want. Then you
run up until the problem and restart with the last checkpoint.
Run for a week without checkpointing? Just begging for trouble.
Craig
the libc backtrace() function or
libbacktrace which can be use from either inside or outside the target
process, these tend to be platform independent.
I started with the libc backtrace function, but wanted something better
than its backtrace_symbols() companion.
libbacktrace is AFAICT also gcc specific. Or do you any pointers to
some more platform-info on libbacktrace ?
I believe it's binutils/libc-specific, not compiler-specific. at least
"pathcc -O3 -fno-inline-functions -g" gave me a meaningful backtrace on
an mpi tester.
anyway, appended is my current version of backtrace.c - I think it's
interesting and potentially useful, especially considering that it's not
really complex:
/* print a backtrace.
written by Mark Hahn, SHARCnet, 2007.
gcc -fPIC backtrace.c /usr/lib64/libbfd-2.15.92.0.2.so -shared -o
backtrace.so
using -lbfd chokes on a symbol addressing issue with (static) libbfd.a
on my system. your libbfd version number may differ.
LD_PRELOAD=./backtrace.so ./tester
signal(11)
Obtained 9 stack frames.
file: /home/hahn/private/tester.c, line: 10, func dosegv
file: /home/hahn/private/tester.c, line: 14, func bar
file: /home/hahn/private/tester.c, line: 17, func foo
file: /home/hahn/private/tester.c, line: 29, func main
all symbols (globals and functions) are static to avoid contamination.
you need -g on the target program, and potentially something like
-fno-inline-functions to dissuade the compiler from disappearing some
functions.
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
#include <execinfo.h>
#include <signal.h>
#include <bfd.h>
#include <unistd.h>
#define MAX_FRAMES (20)
/* globals retained across calls to resolve. */
static bfd* abfd = 0;
static asymbol **syms = 0;
static asection *text = 0;
static void resolve(char *address) {
if (!abfd) {
char ename[1024];
int l = readlink("/proc/self/exe",ename,sizeof(ename));
if (l == -1) {
perror("failed to find executable\n");
return;
}
ename[l] = 0;
bfd_init();
abfd = bfd_openr(ename, 0);
if (!abfd) {
perror("bfd_openr failed: ");
return;
}
/* oddly, this is required for it to work... */
bfd_check_format(abfd,bfd_object);
unsigned storage_needed = bfd_get_symtab_upper_bound(abfd);
syms = (asymbol **) malloc(storage_needed);
unsigned cSymbols = bfd_canonicalize_symtab(abfd, syms);
text = bfd_get_section_by_name(abfd, ".text");
}
long offset = ((long)address) - text->vma;
if (offset > 0) {
const char *file;
const char *func;
unsigned line;
if (bfd_find_nearest_line(abfd, text, syms, offset, &file,
&func, &line) && file)
printf("file: %s, line: %u, func %s\n",file,line,func);
}
}
static void print_trace() {
void *array[MAX_FRAMES];
size_t size;
size_t i;
void *approx_text_end = (void*) ((128+100) * 2<<20);
size = backtrace (array, MAX_FRAMES);
printf ("Obtained %zd stack frames.\n", size);
for (i = 0; i < size; i++) {
if (array[i] < approx_text_end) {
resolve(array[i]);
}
}
}
static void handler(int sig) {
printf("signal(%d)\n",sig);
print_trace();
_exit(1);
}
static void __attribute__((constructor)) init() {
static struct sigaction sa;
sa.sa_handler = handler;
sigaction(SIGABRT, &sa, 0);
sigaction(SIGFPE, &sa, 0);
sigaction(SIGSEGV, &sa, 0);
}
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