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    Subject[RFC BUG?] dereference PAGE_OFFSET address (rc7-mm2)
    Hi.

    I don't know why, but when I'm dereferencing PAGE_OFFSET(0xC0000000 on
    x86) address from user space on rc7-mm2 I don't receive SIGSEGV signal
    and there is no any core dump.
    btw: on poor rc-7 all is ok.

    test_code:
    ---
    #include <stdio.h>
    #include <stdlib.h>
    #include <errno.h>
    #include <unistd.h>
    #include <sys/wait.h>
    #include <sys/time.h>
    #include <sys/resource.h>
    #include <sys/types.h>

    #define PAGE_OFFSET 0xC0000000

    static void _error(const char *msg)
    {
    int errcode = errno;

    fprintf(stderr, "ERROR:\n--> %s [%s]\n", msg, strerror(errcode));
    exit(EXIT_FAILURE);
    }

    int main(void)
    {
    int pid;
    struct rlimit rl;
    int status;

    printf("Trying to cause ELF core dump...\n");

    rl.rlim_cur = rl.rlim_max = 0x10000000;

    if(setrlimit(RLIMIT_CORE, &rl) < 0)
    _error("setrlim error!");
    if((pid = fork()) < 0)
    _error("fork error!");
    else if(pid == 0) {
    *((long*) PAGE_OFFSET ) = 0; /* trying to dereference kernel start address */
    _exit(EXIT_SUCCESS);
    }

    if(waitpid(pid, &status, 0) < 0)
    _error("waitpid error!");
    if(WCOREDUMP(status))
    printf("All is ok. We receive SIGSEGV and core dump has occured.\n");
    else
    printf("All is bad. We don't receive SIGSEGV and core dump hasn't
    occured. (WHY?!)\n"); /* here I just get SIGCHLD, this means that
    child process have made it's work success... */

    exit(EXIT_SUCCESS);
    }
    ---

    [asgard@midgard]$ uname -a
    Linux midgard 2.6.21-rc7-mm2 #5 SMP Wed May 2 04:15:09 MSD 2007 i686 GNU/Linux

    [asgard@midgard]$ ./a.out
    Trying to cause ELF core dump...
    All is bad. We don't receive SIGSEGV and core dump hasn't occured. (WHY?!)

    ---

    [asgard@midgard]$ uname -a
    Linux midgard 2.6.21-rc7 #5 SMP Wed May 2 02:11:50 MSD 2007 i686 GNU/Linux

    [asgard@midgard]$ ./a.out
    Trying to cause ELF core dump...
    All is ok. We receive SIGSEGV and core dump has occured.

    With best regards.
    Dan Kruchinin.
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