Invalid read in mpz_powm_ui

[Torbjorn Granlund]

Emmanuel Thomé <emmanuel.thome at gmail.com> writes:

  Having asm instructions in addmul_1 not supported by valgrind is
  something which annoys gmp users, because it makes it impossible to
  test their code under valgrind (a suggestion to use a plain C gmp is
  valid, though).
  
That'd help for the present ARM problem, but the AMD64 problem is a
result of a compiler-generated instruction (or a library which we link
to).

  My experience is that the valgrind developers are doing a very good
  job at supporting a fair share of the instructions which show up, but
  they can't always be exhaustive. If we, as users of gmp for instance,
  are impacted by some missing instructions, a nice thing to do is to
  provide the fix by ourselves.

I looked into adding umaal, but it seems like I would have to make lots
of guesses or spend many hours.  (It is dataflow-wise equivalent to the
supported umlal, but I am not sure it can be handled identically.)

-- 
Torbjörn