[Bug gdb/27806] free(): invalid pointer during gdb.ada/fixed_cmp.exp

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=27806

--- Comment #3 from Tom de Vries <vries at gcc dot gnu.org> ---
Hmm, so it seems to be related to this bit of code in gdb_mpz::safe_export:
...
147       gdb::unique_xmalloc_ptr<void> exported
148         (mpz_export (NULL, &word_countp, -1 /* order */, buf.size () /*
size */,
149                      endian, 0 /* nails */, exported_val.val));
...

The gdb::unique_xmalloc_ptr<void> makes sure that free is called on
exported.get ().

But when I step into the allocation:
...
(gdb) s
__gmpz_export (data=0x0, countp=0x7fffffffcee8, order=-1, size=4, endian=-1,
nail=0, z=0x7fffffffcef0) at mpz/export.c:50
Downloading source file /usr/src/debug/gmp-6.2.1-3.1.x86_64/mpz/export.c...
  ...
79          data = (*__gmp_allocate_func) (count*size);
...
it seems that it uses a garbage-collect malloc from libguile:
...
(gdb) s
custom_gmp_malloc (alloc_size=4) at numbers.c:240
Downloading source file
/usr/src/debug/guile-3.0.5-2.4.x86_64/libguile/numbers.c...
240       return scm_gc_malloc_pointerless (alloc_size, "GMP");
(gdb) s
scm_gc_malloc_pointerless (size=4, what=0x7ffff7ee970f "GMP") at
gc-malloc.c:210
Downloading source file
/usr/src/debug/guile-3.0.5-2.4.x86_64/libguile/gc-malloc.c...
210       return do_gc_malloc_atomic (size, what);
(gdb) s
do_gc_malloc_atomic (what=0x7ffff7ee970f "GMP", size=4) at gc-malloc.c:92
92        return GC_MALLOC_ATOMIC (size ? size : sizeof (void *));
(gdb) s
0x00007ffff7e2c2e8 in GC_malloc_atomic@plt () from /usr/lib64/libguile-3.0.so.1
...

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