mmap.c

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include <ucontext.h>

void sighandler(int signum, siginfo_t* info, ucontext_t* ctxt) {
        printf("handler %d  addr=%p  rip=%#x\n", signum, info->si_addr, ctxt->uc_mcontext.gregs[REG_RIP]);
        signal(signum, SIG_DFL);
        kill(getpid(), signum);
}

int main(int argc, char *argv[]) {
        struct sigaction sa_new = {0};
        sa_new.sa_sigaction = (void (*)(int, siginfo_t*, void *))sighandler;
        sa_new.sa_flags = SA_ONESHOT | SA_SIGINFO;
        sigaction(SIGSEGV, &sa_new, 0);

        int total_pages = argc > 1 ? atoi(argv[1]) : 10;
        int page_to_unmap = argc > 2 ? atoi(argv[2]) : 0;

        int section = shm_open("section", O_RDWR | O_CREAT, (mode_t)0600);
        if(section == -1) {
                perror("Error creating section");
                exit(EXIT_FAILURE);
        }
        if(ftruncate(section, total_pages * getpagesize()) == -1) {
                perror("Error setting section size");
                exit(EXIT_FAILURE);
        }

        int* map = mmap(0, total_pages * getpagesize(), PROT_READ | PROT_WRITE, MAP_SHARED, section, 0);

        printf("memory mapped at %p\n", map);

        if(map == MAP_FAILED) {
                perror("Error creating mmap");
                exit(EXIT_FAILURE);
        }
        for(int i = 0; i < (total_pages * getpagesize()) / sizeof(int); ++i) {
                map[i] = 2 * i;
        }

        void* target = map + (page_to_unmap * (getpagesize() / sizeof(int)));

        printf("unmapping single page at %p\n", target);

        if(munmap(target, getpagesize()) == -1) {
                perror("Error unmapping page.");
                exit(EXIT_FAILURE);
        }

        for(int i = 0; i < (total_pages * getpagesize()) / sizeof(int); ++i) {
                map[i] = 2 * i;
        }

        if(munmap(map, total_pages * sizeof(int)) == -1) {
                perror("Error unmapping the memory.");
                exit(EXIT_FAILURE);
        }

        close(section);
        shm_unlink("section");
        return 0;
}