shm_testcase.c

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/file.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <unistd.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

static void fail_(const char *message, const char *file, size_t line) {
    fprintf(stderr, "failed: %s %s (%s:%zu)\n", message, strerror(errno), file, line);
    abort();
}
#define fail(X) fail_((X), __FILE__, __LINE__)

int main(int argc, char **argv) {
    // got restart, grab the fd and print leet
    if (!strncmp(*argv, "-r", 2)) {
        argv++;
        struct stat buf;
        int fd;
        char *scan = &argv[0][2];
        sscanf(scan, "%d", &fd);
        if (fstat(fd, &buf) != 0) fail("fstat");

        void *mem = mmap(0, buf.st_size, PROT_READ, MAP_SHARED, fd, 0);
        if (mem == MAP_FAILED) fail("mmap");

        if (munmap(mem, buf.st_size) != 0) fail("munmap");
        if (shm_unlink("test_case") != 0) fail("shm_unlink");

        printf("%d!\n", *((int*)mem));
        return EXIT_SUCCESS;
    }

    // get shared memory (create trun read/write)
    int fd = shm_open("test_case", O_CREAT | O_TRUNC | O_RDWR, 0666);
    if (fd == -1) fail("shm_open");

    // unset FD_CLOEXEC
    int flags = fcntl(fd, F_GETFD);
    flags &= ~FD_CLOEXEC;
    fcntl(fd, F_SETFD, flags);

    // rounded to nearest page multiply alloc (sizeof(int) chars for testcase)
    // will become PAGE_SIZE in this case.
    size_t size = sizeof(int);
    const size_t pagesize = sysconf(_SC_PAGE_SIZE);
    size = ((size + pagesize - 1) / pagesize) * pagesize;

    // truncate
    int truncate = ftruncate(fd, size);
    if (truncate != 0) fail("ftruncate");

    // grab the memory
    void *memory = mmap(0, pagesize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (memory == MAP_FAILED) fail("mmap");

    // write leet
    *((int*)memory) = 1337;

    // run the process now
    char buffer[1024];
    snprintf(buffer, sizeof(buffer), "-r%d", fd);
    execv(*argv, (char *[]){ buffer, *argv, (char *)0 });
}