Re: [PATCH] PR fortran/105310 - ICE when UNION is after the 8th field in a DEC STRUCTURE with -finit-derived -finit-local-zero

[Harald Anlauf <anlauf@gmx.de>]

Hi Fritz,

Am 20.04.22 um 20:03 schrieb Fritz Reese via Fortran:
> See the bug report at gcc dot gnu dot org/bugzilla/show_bug.cgi?id=105310 .
>
> This code was originally authored by me and the fix is trivial, so I
> intend to commit the attached patch in the next few days if there is
> no dissent.

OK if you add a/the testcase.

>
> The bug is caused by gfc_conv_union_initializer in
> gcc/fortran/trans-expr.cc, which accepts a pointer to a vector of
> constructor trees (vec<constructor_elt, va_gc>*) as an argument, then
> appends one or two field constructors to the vector. The problem is
> the use of CONSTRUCTOR_APPEND_ELT(v, ...) within
> gfc_conv_union_initializer, which modifies the vector pointer v when a
> reallocation of the vector occurs, but the pointer is passed by value.
> Therefore, when a vector reallocation occurs, the caller's
> (gfc_conv_structure) vector pointer is not updated and subsequently
> points to freed memory. Chaos ensues.
>
> The bug only occurs when gfc_conv_union_initializer itself triggers
> the reallocation, which is whenever the vector is "full"
> (v->m_vecpfx.m_alloc == v->m_vecpfx.m_num). Since the vector defaults
> to allocating 8 elements and doubles in size for every reallocation,
> the bug only occurs when there are 8, 16, 32, etc... fields with
> initializers prior to the union, causing the vector of constructors to
> be resized when entering gfc_conv_union_initializer. The
> -finit-derived and -finit-local-zero options together ensure each
> field has an initializer, triggering the bug.
>
> The patch fixes the bug by passing the vector pointer to
> gfc_conv_union_initializer by reference, matching the signature of
> vec_safe_push from within the CONSTRUCTOR_APPEND_ELT macro.
>
> --
> Fritz Reese

As this affects all branches, you may backport the patch as far as
you feel reasonable.  (No, I do not use DEC extensions personally.)

Thanks for the patch!

Harald