avoiding abort in libgmp

问题

I have some code that uses libgmp. At some point the user may request a factorial of a very large number. Unfortunately, this results in libgmp raising an abort signal.

For example the following code:

#include <cmath>
#include <gmp.h>
#include <iostream>

int main() {

    mpz_t result;
    mpz_init(result);

    mpz_fac_ui(result, 20922789888000);

    std::cout << mpz_get_si(result) << std::endl;
}

Results in:

$ ./test 
gmp: overflow in mpz type
Aborted

Apparently, the number produced is REALLY big. Is there anyway to handle the error more gracefully than an abort. This is a GUI based application and it aborting is pretty much the least desirable way to handle this sort of issue.

回答1:

The best way to handle these errors gracefully in your application is probably to fork off a helper process to perform the GMP calculations. If the helper process is killed by SIGABRT, your parent process can detect that and report an error to the user.

(The below is my original answer, which has "undefined results" according to the GMP documentation - it is left here for completeness).

You can catch the error if you install a signal handler for SIGABRT that uses longjmp():

jmp_buf abort_jb;

void abort_handler(int x)
{
    longjmp(abort_jb, 1);
}

int dofac(unsigned long n)
{
    signal(SIGABRT, abort_handler);
    if (setjmp(abort_jb))
        goto error;

    mpz_t result;
    mpz_init(result);

    mpz_fac_ui(result, 20922789888000);

    std::cout << mpz_get_si(result) << std::endl;

    signal(SIGABRT, SIG_DFL);
    return 0;

    error:
    signal(SIGABRT, SIG_DFL);
    std::cerr << "Caught SIGABRT from GMP.\n";
    return 1;
}

回答2:

It would appear that you are out of luck, based on the code in mpz/realloc.c and mpz/realloc2.c. If too much memory was requested, it just does this:

if (UNLIKELY (new_alloc > INT_MAX))
  {
    fprintf (stderr, "gmp: overflow in mpz type\n");
    abort ();
  }

回答3:

Overwrite abort() with LD_PRELOAD.

What is the LD_PRELOAD trick?

Edit: To make the answer more self-contained, I copy the text of that answer here:

If you set LD_PRELOAD to the path of a shared object, that file will be loaded before any other library (including the C runtime, libc.so). So to run ls with a your special malloc() implementation, do this:

$ LD_PRELOAD=/path/to/my/malloc.so /bin/ls

Credits to JesperE.

来源：https://stackoverflow.com/questions/3558684/avoiding-abort-in-libgmp

标签

c++

gmp