[users@httpd] Seg fault when assigning value in AP_INIT_TAKE1 callback

[Allasso Travesser]

Hello,

Learning to create modules, I want to read configuration directives. I used the 
following example out of “The Apache Modules Book” (Nick Kew).  It compiles 
fine, however, when I restart apache, I get segmentation fault:

sudo service apache2 restart
Segmentation fault (core dumped)
Action 'configtest' failed.
The Apache error log may have more information.
   …fail!

log shows this:

[Sun Dec 08 03:58:04 2013] [notice] child pid 30080 exit signal Segmentation 
fault (11), possible coredump in /etc/apache2

The fault seems to be a result of this line of code (no error results if it is 
removed):

  ((txt_cfg*)cfg)->header = val ;

Here is my code (reduced to minimal test case):


#include "httpd.h"
#include "http_config.h"
#include "http_protocol.h"

typedef struct txt_cfg {
  const char* header ;
  const char* footer ;
} txt_cfg;

static const char* get_form_path(cmd_parms* cmd, void* cfg,
  const char* val) {
  ((txt_cfg*)cfg)->header = val ;
  return NULL ;
}

static const command_rec mod_cmds[] = {
  AP_INIT_TAKE1("CustomAuthFormPath", get_form_path, NULL, OR_ALL,
        "Path to custom authorization form"),
  { NULL }
};

static void register_hooks(apr_pool_t *pool)
{
}

module AP_MODULE_DECLARE_DATA customauthform_module =
{
    STANDARD20_MODULE_STUFF,
    NULL,
    NULL,
    NULL,
    NULL,
    mod_cmds,
    register_hooks,
};

If anyone knows the reason for this I would surely appreciate understanding.

Thank you kindly,

Allasso