memory stack problem Post: 80773

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Top Forums Programming memory stack problem Post 80773 by Driver on Thursday 11th of August 2005 12:39:43 PM

08-11-2005

Registered User

Here's what I use to catch accidental variable modifications from other functions:

Code:

#include <sys/types.h>
#include <sys/mman.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

void *
debug_alloc_pages(size_t nbytes) {
        long    psize = sysconf(_SC_PAGESIZE);
        size_t  npages = nbytes / psize;
        int             fd;
        void    *ret;

        if (npages * psize < nbytes) {
                ++npages;
        }

#ifdef MAP_ANON
        ret = mmap(0, npages * psize, PROT_READ|PROT_WRITE,
                MAP_ANON, -1, 0);
        if (ret == MAP_FAILED) {
                perror("mmap");
                exit(EXIT_FAILURE);
        }
#else
        /*
         * Use MAP_ANONYMOUS on HP-UX and mmap() with an 
         * fd for /dev/zero everywhere else
         */
        puts("debug_alloc_pages() does not work on this system");
        exit(EXIT_FAILURE);
#endif
        return ret;
}

Now, instead of writing

char buf[128];

... write

char *buf = debug_alloc_pages(128);

When you're done initializing ``buf'', do

(void) mprotect(buf, sysconf(_SC_PAGE_SIZE), PROT_READ);

In every function that is allowed to modify ``buf'', execute an

(void) mprotect(buf, sysconf(_SC_PAGE_SIZE), PROT_READ|PROT_WRITE);

... when you enter it and

(void) mprotect(buf, sysconf(_SC_PAGE_SIZE, PROT_READ);

... when you return from it.

An invalid write access should now yield a bus error or segmentation fault which will provide you with a core dump from which you can obtain a stack trace showing you which function attempted to modify the data.

Hope this helps

Driver

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abrt-auto-reporting

ABRT-AUTO-REPORTIN(1)						    ABRT Manual 					     ABRT-AUTO-REPORTIN(1)

NAME

       abrt-auto-reporting - Get or modify a value of the auto reporting option

SYNOPSIS

       abrt-auto-reporting [-v] [ enabled | yes | 1 | disabled | no | 0 ]

DESCRIPTION

       Reads the configuration from abrt.conf and saves the changes to the same file.

       The changes will take effect immediately without necessity to restart any ABRT process and will be persistent.

       disabled
	   User have to report the detect problems manually

       enabled
	   ABRT uploads an uReport which was generated for a detected problem immediately after the detection phase.

   uReport description
       ABRT supports uReports for four types of crashes: crashes of C/C++ programs that result in a core dump, uncaught Python exceptions,
       uncaught Java exceptions and kernel oopses.

       Each uReport generally contains a stack trace, or multiple stack traces in the case of multi-threaded C/C++ and Java programs. The stack
       trace only describes the call stack of the program at the time of the crash and does not contain contents of any variables.

       Every uReport also contains identification of the operating system, versions of the RPM packages involved in the crash, and whether the
       program ran under a root user.

       There are also items specific to each crash type:

       C/C++ crashes
	   these are path to the executable and signal delivered to the program,

       Python exceptions
	   there is the type of the exception (without the error message, which may contain sensitive data),

       for kernel oopses
	   these are list of loaded kernel modules, list of taint flags, and full text of the kernel oops.

       Warning: The full text of a kernel oops might contain information like the identification of the host hardware type. You should disable the
       autoreporting feature if you do not want to share this information with Red Hat.

OPTIONS

       -v, --verbose
	   Be more verbose. Can be given multiple times.

SEE ALSO

       abrt.conf(5)

AUTHORS

       o   ABRT team

abrt 2.1.11							    06/18/2014						     ABRT-AUTO-REPORTIN(1)