This will explain how to debug segmentation faults caused by mod_php.

  1. use
    strace, truss, kdump/ktrace
    on httpd children and you will probably see the php filename causing the issue

  2. Set CoreDumpDirectory on one of the crashing systems

  3. Make sure you have debugging symbols. On Redhat/CentOS you will need to install -debuginfo RPM (for apache/httpd AND php/mod_php)
  4. echo 1 > /proc/sys/fs/suid_dumpable

  5. Run
    gdb httpd core.1234

  6. Now run
    bt

  7. and examine the
    opline
    tips for php/gdb
  8. print *opline
    print opline->op2.u.constant.value.str.val
    print opline->op1.u.constant.value.str.val
    
    In my case (and the one below) op1 started with a null byte, so you needed to run:
    print opline->op1.u.constant.value.str.val+1
    
    And you will get the php file name and, probably, the function which is causing the issue.