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    SubjectRe: core files
    On 981230, Michael Elizabeth Chastain wrote:
    > You could do a lot of *this* in user space by having a library function
    > set the default value for all signals, or just SIGSEGV, to a function
    > that uses some kind of IPC, such as writing to a fifo whose name includes
    > the uid. I wonder if it's possible to use preloading to inject that
    > snippet of code into an existing executable without relinking it and
    > without touching libc.

    Yes. The only hard part I see is getting the executable filename.
    core.c:
    ---
    #include <stdlib.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <fcntl.h>
    #include <signal.h>
    #include <unistd.h>

    void init_libcore(void) __attribute__((constructor));

    void
    sighandler(int signo)
    {
    struct {
    int signo;
    pid_t pid;
    } s;
    int fd;

    s.signo = signo;
    s.pid = getpid();
    fd = open(getenv("SIG_FIFO"), O_WRONLY);
    write(fd, &s, sizeof s);
    close(fd);
    pause();
    }

    void
    init_libcore(void)
    {
    struct sigaction act;

    act.sa_handler = sighandler;
    sigfillset(&act.sa_mask);
    act.sa_flags = SA_RESETHAND;
    sigaction(SIGSEGV, &act, NULL);
    }
    -----
    % gcc -fPIC -o core.o -c core.c
    % gcc -shared -o core.so core.o
    % LD_PRELOAD=./core SIG_FIFO=$HOME/.crash_handler_fifo bash

    A program to listen to the fifo should be straightforward.
    --
    ICQ UIN: 56155810

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