/*
 * Copyright 2002-2019 Intel Corporation.
 * 
 * This software is provided to you as Sample Source Code as defined in the accompanying
 * End User License Agreement for the Intel(R) Software Development Products ("Agreement")
 * section 1.L.
 * 
 * This software and the related documents are provided as is, with no express or implied
 * warranties, other than those that are expressly stated in the License.
 */

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

FILE* log_fd;

void PrintAndCompareAlternateStack(const char* prefix, const stack_t* compare_stack) {
    stack_t sigstk;

    int sigalt_result = sigaltstack(NULL, &sigstk);

    fprintf(log_fd,"%s: sigalt_result == %d {ss_sp=%p; ss_size=%d; ss_flags=%x}\n",
            prefix, sigalt_result, sigstk.ss_sp, (int)sigstk.ss_size, sigstk.ss_flags);
    fflush(log_fd);

    if (sigalt_result < 0){
        perror("ERROR printing alternate stack");
    }
    if (!sigstk.ss_sp) {
        fprintf(stderr,"%s: NO alternate stack\n", prefix);
    }
    if (compare_stack) {
        fprintf(stderr,"%s: current stack %s compare_stack\n",
                prefix,
                ((sigstk.ss_sp == compare_stack->ss_sp) && sigstk.ss_size == compare_stack->ss_size)?
                "equals to":"different from");
    }
    fflush(stderr);
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        printf("Usage %s <log_file_name>\n", argv[0]);
        exit(1);
    }

    log_fd = fopen(argv[1], "a");
    if (log_fd < 0 ) {
        perror("Could not open log file");
        exit(1);
    }
    fprintf(log_fd, "Start running forktest_altstack.c\n");

    // set current alternate stack
    stack_t sigstk;
    sigstk.ss_sp = malloc(SIGSTKSZ);
    void * ss_sp = sigstk.ss_sp;

    if (sigstk.ss_sp == NULL) { 
        fprintf(stderr,"Could not allocate ss_sp\n");
        return -1;
    }
    sigstk.ss_size = SIGSTKSZ;
    sigstk.ss_flags = 0;

    sigaltstack(&sigstk, NULL);

    PrintAndCompareAlternateStack("Father", NULL);

    int pid = fork();
    if (pid < 0 ) {
        perror("Couldn't fork");
        exit(1);
    } else if (pid == 0) {
        //child process - print sigaltstack
        PrintAndCompareAlternateStack("child process printing" , &sigstk);
        fclose(log_fd);
    } else {
        waitpid(pid, NULL, 0);
        //pid > 0 => father process (free pointer)
        if (ss_sp) free(ss_sp);
        fclose(log_fd);
    }

    return 0;
}