mpz_mul memory allocation bug

[Torbjörn Granlund]

Daniel Kochmański <dkochmanski at turtle-solutions.eu> writes:

  I've encontered problem with GMP 6.0.0 when used with ECL (Embeddable
  Common-Lisp). Memory is managed by bdwgc and gmp seems to allocate
  memory somewhere, where it shouldn't, resulting in:
  
    (SIGABRT) "Duplicate large block deallocation"
  
OK. so GMP allocates memory where it shouldn't (whatever that means) and
a LISP system as a result deallocates a memory area twice...  Your line
of reasoning is not crystal clear.  :-)

  Problem is absent in GMP 4.2.1. After tracking problem, I've came to
  conclusion, that it is caused by `mpn_fft_mul', which is called by
  `mpn_sqr', being optimization for corner-case, when `mpz_mul' is called
  with the same bignum as second and third argument.
  
  Removing optimization "fixes" problem. `mpn_fft_mul' is called, when
  size n isn't below `SQR_FFT_THRESHOLD', and comment:
  
    /* The current FFT code allocates its own space.  That should probably
       change.  */
  
  might be a clue, that this is a place of problem.
  
This comment does not say that we knowingly do something that is buggy.
It is rather a suggestion for a code cleanup.

If you have a self-contained tests case for GMP where it misbehaves,
please report it to us.

You present report is nothing we can work with, I'm afraid.

-- 
Torbjörn
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