C Strange behaviour on 64-bit server

Question

Hi,

I have this strange behaviour in Apache post_config handler :

int setup_module(apr_pool_t *p, apr_pool_t *plog, apr_pool_t *ptemp,server_rec *s)
{
    //1
    my_config_t *config =  ap_get_module_config(s->module_config, &my_module);

    //2
    log_me(config->logfp, apr_psprintf(ptemp, "My module version %s\n", MY_VERSION));

    //3
    log_me(config->logfp, "Starting the batch job");

    return OK;
}

log_me is a custom function declared in another file and declared in the header (it is resolved at compile time).

In the step2 I can see that config has a valid value, however step 3 fails with a SEGSEGV and if I try to debug it I can see this :

//step 2 gdb: print config $1 = (my_config_t *)0x7a8098

//step 3 gdb: print config Cannot access memory at address 0x38

Answer 1

Something is overwriting the config pointer. Can you put a breakpoint on the memory location and see what is executing the overwrite? Here's a guide to how to do this: http://www.technochakra.com/debugging-types-of-data-breakpoints-in-gdb/

Answer 2

I've found teh problem.

In log_me I was making :

int nbytes = strlen(message);

instead of:

apr_size_t nbytes = strlen(message);

Being on 64 bits this screwed all.. no idea why yet.

Answer 3

What is ptemp passed into setup_module, and is it safe to use it as a buffer for your sprintf? Is it possible ptemp points to a memory area that isn't large enough to hold that string?

Maybe you should declare an auto variable (char buffer[80];) and use that for your sprintf?