I'm debugging a segfault in my php app, I compiled php with --enable-debug option and after php-fpm dumped core during the segfault, I run:
$ gdb /usr/local/sbin/php-fpm core
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Reading symbols from /usr/local/sbin/php-fpm...(no debugging symbols found)...done.
[New LWP 2110]
warning: Can't read pathname for load map: No error information.
Core was generated by `php-fpm:'.
Program terminated with signal SIGBUS, Bus error.
#0 0x000055c27ba1f291 in ?? ()
(gdb) bt
#0 0x000055c27ba1f291 in ?? ()
#1 0x000055c27ba21bce in _efree ()
#2 0x000055c27ba6c8b2 in ?? ()
#3 0x000055c27ba70cee in zend_array_destroy ()
#4 0x000055c27ba56fbd in _zval_dtor_func ()
#5 0x000055c27ba6cce4 in ?? ()
#6 0x000055c27ba70cc8 in zend_array_destroy ()
#7 0x000055c27ba56fbd in _zval_dtor_func ()
#8 0x000055c27ba6cce4 in ?? ()
#9 0x000055c27ba70c8a in zend_array_destroy ()
#10 0x000055c27ba56fbd in _zval_dtor_func ()
#11 0x000055c27ba6cce4 in ?? ()
#12 0x000055c27ba70cc8 in zend_array_destroy ()
#13 0x000055c27ba56fbd in _zval_dtor_func ()
#14 0x000055c27ba44b75 in ?? ()
#15 0x000055c27ba450fe in zend_cleanup_user_class_data ()
#16 0x000055c27ba3f473 in ?? ()
#17 0x000055c27ba5971b in zend_deactivate ()
#18 0x000055c27b9bf1df in php_request_shutdown ()
#19 0x000055c27bb55015 in ?? ()
#20 0x00007f7fb743e964 in __libc_start_main () from /lib/ld-musl-x86_64.so.1
#21 0x0000000000000000 in ?? ()
I also put .gdbinit from php sources to the directory with core file and set set auto-load safe-path / to ~/.gdbinit (not sure how it helps though).
As you can see there are ?? in the backtrace which is not helpful at all. Is this how it should be? Is there any way to get the real caller?
Is this how it should be?
No.
Is there any way to get the real caller?
Probably.
Your stack trace indicates that /usr/local/sbin/php-fpm is fully-stripped (has its symbol table removed). You can confirm this with file /usr/local/sbin/php-fpm.
It is not uncommon for make install to fully strip binaries. You should try to use the "as built" binary (instead of "as installed" you are doing now): gdb /path/to/build/tree/php-fpm core.