backtrace.c

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/*
 *   This library is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU Lesser General Public
 *   License as published by the Free Software Foundation; either
 *   version 2.1 of the License, or (at your option) any later version.
 *
 *   This library is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 *   Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser General Public
 *   License along with this library; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/** Functions which we wish were included in the standard talloc distribution
 *
 * @file src/lib/util/backtrace.c
 *
 * @copyright 2026 The FreeRADIUS server project
 */
RCSID("$Id: 7c24e08f3d6f68a6cbca35268f3e3c8e20ce7102 $")
 
#include <dlfcn.h>
 
#include <freeradius-devel/util/backtrace.h>
#include <freeradius-devel/util/debug.h>
#include <freeradius-devel/util/file.h>
 
#ifdef HAVE_BACKTRACE
#  include <freeradius-devel/backtrace/backtrace.h>
 
static struct backtrace_state *backtrace_state = NULL;  //!< Backtrace state for the backtrace functions
                                                        ///< This is initialised to be thread-safe, so we only need one.
 
/** Used when building without libbacktrace to record frame information
 */
typedef struct {
        char const      *library;                       //!< Backtrace library name.
        char const      *filename;                      //!< Backtrace file.
        char const      *function;                      //!< Backtrace function.
        bool            function_guess;                 //!< Whether dladdr guessed the function.
                                                        //!< This is true if the function name is not in the
                                                        //!< symbol table, but was guessed from the program counter.
        unsigned int    lineno;                         //!< Backtrace line number.
        unsigned int    frameno;                        //!< Backtrace frame number.
        uintptr_t       pc;                             //!< Backtrace program counter.
} fr_bt_info_frame_t;
#elif defined(HAVE_EXECINFO)
#  include <execinfo.h>
#endif
 
#  ifndef MAX_BT_FRAMES
#    define MAX_BT_FRAMES 128
#  endif
#  ifndef MAX_BT_CBUFF
#    define MAX_BT_CBUFF  1048576                       //!< Should be a power of 2
#  endif
 
static pthread_mutex_t fr_backtrace_lock = PTHREAD_MUTEX_INITIALIZER;
 
typedef struct {
        void                    *obj;                           //!< Memory address of the block of allocated memory.
#ifdef HAVE_BACKTRACE
        fr_bt_info_frame_t      *frames[MAX_BT_FRAMES];         //!< Backtrace frame data
#else
        void                    *frames[MAX_BT_FRAMES];         //!< Backtrace frame data
#endif
        int                     count;                          //!< Number of frames stored
} fr_bt_info_t;
 
struct fr_bt_marker {
        void            *obj;                           //!< Pointer to the parent object, this is our needle
                                                        //!< when we iterate over the contents of the circular buffer.
        fr_fring_t      *fring;                         //!< Where we temporarily store the backtraces
};
 
#ifdef HAVE_BACKTRACE
/** Log faults from libbacktrace
 *
 */
static void _backtrace_error(UNUSED void *data, const char *msg, int errnum)
{
        FR_FAULT_LOG("Backtrace error: %s (%d)", msg, errnum);
}
 
static void backtrace_info_sanitise(fr_bt_info_frame_t *info)
{
        Dl_info dl_info;
 
        if (dladdr((void *)info->pc, &dl_info) != 0) {
                info->library = dl_info.dli_fname;
                if (!info->function) {
                        info->function = dl_info.dli_sname;
                        info->function_guess = true;
                }
        }
}
 
static void backtrace_info_print(fr_bt_info_frame_t *frame, int fd, bool trim_path)
{
        if (!frame->library && !frame->filename) {
                dprintf(fd, "#%u: 0x%lx\n",
                        frame->frameno,
                        (unsigned long)frame->pc);
                return;
        }
        else if (!frame->filename) {
                dprintf(fd, "#%u: 0x%lx %s in %s()\n",
                        frame->frameno,
                        (unsigned long)frame->pc,
                        trim_path ? fr_filename(frame->library) : frame->library,
                        frame->function ? frame->function : "??");
                return;
        }
        dprintf(fd, "#%u: 0x%lx %s in %s() at %s:%d\n",
                frame->frameno,
                (unsigned long)frame->pc,
                trim_path ? fr_filename(frame->library) : frame->library,
                frame->function ? frame->function : "??",
                trim_path ? fr_filename_common_trim(frame->filename, frame->library) : frame->filename,
                frame->lineno);
 
}
 
static int _backtrace_info_record(void *data, uintptr_t pc,
                                  const char *filename, int lineno,
                                  const char *function)
{
        fr_bt_info_t *info = talloc_get_type_abort(data, fr_bt_info_t);
        fr_bt_info_frame_t *frame;
 
        if (info->count >= (int)NUM_ELEMENTS(info->frames)) return 0;
 
        frame = talloc_zero(info, fr_bt_info_frame_t);
        if (!frame) return -1;
 
        frame->filename = talloc_strdup(frame, filename);
        frame->function = talloc_strdup(frame, function);
        frame->lineno = lineno;
        frame->frameno = info->count;
        frame->pc = pc;
 
        backtrace_info_sanitise(frame);
 
        info->frames[info->count++] = frame;
 
        return 0;
}
 
static void backtrace_record(fr_bt_info_t *info)
{
        backtrace_full(backtrace_state, 0, _backtrace_info_record, _backtrace_error, info);
}
 
static int _backtrace_print(void *data, uintptr_t pc,
                            const char *filename, int lineno,
                            const char *function)
{
        unsigned int *frame_no = ((unsigned int *)data);
        fr_bt_info_frame_t frame = {
                .filename = filename,
                .lineno = lineno,
                .function = function,
                .frameno = *frame_no,
                .pc = pc,
        };
 
        backtrace_info_sanitise(&frame);
        backtrace_info_print(&frame, fr_fault_log_fd, true);
 
        (*frame_no)++;
        return 0;
}
 
void fr_backtrace(void)
{
        unsigned int frame = 0;
 
        if ((fr_fault_log_fd >= 0) && backtrace_state) {
                FR_FAULT_LOG("Backtrace:");
                backtrace_full(backtrace_state, 0, _backtrace_print, _backtrace_error, &frame);
        }
}
#elif defined(HAVE_EXECINFO)
void fr_backtrace(void)
{
        /*
         *      Produce a simple backtrace - They're very basic but at least give us an
         *      idea of the area of the code we hit the issue in.
         *
         *      See below in fr_fault_setup() and
         *      https://sourceware.org/bugzilla/show_bug.cgi?id=16159
         *      for why we only print backtraces in debug builds if we're using GLIBC.
         */
#if (!defined(NDEBUG) || !defined(__GNUC__))
        if (fr_fault_log_fd >= 0) {
                size_t frame_count;
                void *stack[MAX_BT_FRAMES];
 
                frame_count = backtrace(stack, MAX_BT_FRAMES);
 
                FR_FAULT_LOG("Backtrace of last %zu frames:", frame_count);
 
                backtrace_symbols_fd(stack, frame_count, fr_fault_log_fd);
        }
#endif
        return;
}
#else
void fr_backtrace(void)
{
        return;
}
#endif
 
#if defined(HAVE_BACKTRACE) || defined(HAVE_EXECINFO)
/** Print backtrace entry for a given object
 *
 * @param fring to search in.
 * @param obj pointer to original object
 */
void fr_backtrace_print(fr_fring_t *fring, void *obj)
{
        fr_bt_info_t *p;
        bool found = false;
 
        while ((p = fr_fring_next(fring))) {
                if ((p->obj == obj) || !obj) {
                        found = true;
 
                        fprintf(stderr, "Stacktrace for: %p\n", p->obj);
#ifdef HAVE_BACKTRACE
                        {
                                int i;
 
                                for (i = 0; i < p->count; i++) {
                                        backtrace_info_print(p->frames[i], fr_fault_log_fd, true);
                                }
                        }
#else
                        backtrace_symbols_fd(p->frames, p->count, fr_fault_log_fd);
#endif
                }
        }
 
        if (!found) {
                fprintf(stderr, "No backtrace available for %p", obj);
        }
}
 
/** Generate a backtrace for an object
 *
 * If this is the first entry being inserted
 */
static int _backtrace_do(fr_bt_marker_t *marker)
{
        fr_bt_info_t *bt;
 
        if (!fr_cond_assert(marker->obj) || !fr_cond_assert(marker->fring)) return -1;
 
        bt = talloc_zero(NULL, fr_bt_info_t);
        if (!bt) return -1;
 
        bt->obj = marker->obj;
#ifdef HAVE_BACKTRACE
        backtrace_record(bt);
#else
        bt->count = backtrace(bt->frames, MAX_BT_FRAMES);
#endif
        fr_fring_overwrite(marker->fring, bt);
 
        return 0;
}
 
/** Inserts a backtrace marker into the provided context
 *
 * Allows for maximum laziness and will initialise a circular buffer if one has not already been created.
 *
 * Code augmentation should look something like:
@verbatim
        // Create a static fring pointer, the first call to backtrace_attach will initialise it
        static fr_fring_t *my_obj_bt;
 
        my_obj_t *alloc_my_obj(TALLOC_CTX *ctx) {
                my_obj_t *this;
 
                this = talloc(ctx, my_obj_t);
 
                // Attach backtrace marker to object
                backtrace_attach(&my_obj_bt, this);
 
                return this;
        }
@endverbatim
 *
 * Then, later when a double free occurs:
@verbatim
        (gdb) call backtrace_print(&my_obj_bt, <pointer to double freed memory>)
@endverbatim
 *
 * which should print a limited backtrace to stderr. Note, this backtrace will not include any argument
 * values, but should at least show the code path taken.
 *
 * @param fring this should be a pointer to a static *fr_fring_buffer.
 * @param obj we want to generate a backtrace for.
 */
fr_bt_marker_t *fr_backtrace_attach(fr_fring_t **fring, TALLOC_CTX *obj)
{
        fr_bt_marker_t *marker;
 
        if (*fring == NULL) {
                pthread_mutex_lock(&fr_backtrace_lock);
                if (*fring == NULL) *fring = fr_fring_alloc(NULL, MAX_BT_CBUFF, true);
                pthread_mutex_unlock(&fr_backtrace_lock);
        }
 
        marker = talloc(obj, fr_bt_marker_t);
        if (!marker) {
                return NULL;
        }
 
        marker->obj = (void *) obj;
        marker->fring = *fring;
 
        fprintf(stderr, "Backtrace attached to %s %p\n", talloc_get_name(obj), obj);
        /*
         *      Generate the backtrace for memory allocation
         */
        _backtrace_do(marker);
        talloc_set_destructor(marker, _backtrace_do);
 
        return marker;
}
#else
fr_bt_marker_t *fr_backtrace_attach(UNUSED fr_fring_t **fring, UNUSED TALLOC_CTX *obj)
{
        fprintf(stderr, "Server built without fr_backtrace_* support, requires execinfo.h and possibly -lexecinfo, or libbacktrace\n");
        abort();
}
#endif
 
void fr_backtrace_init(
#ifndef HAVE_BACKTRACE
                        UNUSED
#endif
                        char const *program)
{
#ifdef HAVE_BACKTRACE
                /*
                 *  Initialise the state for libbacktrace.  As per the docs
                 *  these resources can never be freed, and should be ignore
                 *  in any leak tracking code.
                 */
                backtrace_state = backtrace_create_state(program, 1, _backtrace_error, NULL);
#elif defined(HAVE_EXECINFO) && defined(__GNUC__) && !defined(NDEBUG)
               /*
                *  We need to pre-load lgcc_s, else we can get into a deadlock
                *  in fr_fault, as backtrace() attempts to dlopen it.
                *
                *  Apparently there's a performance impact of loading lgcc_s,
                *  so only do it if this is a debug build.
                *
                *  See: https://sourceware.org/bugzilla/show_bug.cgi?id=16159
                */
                {
                        void *stack[10];
 
                        backtrace(stack, 10);
                }
#endif
}