On Thu, Mar 11, 2021 at 03:47:17PM -0600, Qing Zhao wrote:
> Hi, Kees,
>
> Sorry for the late reply (I have been busy with other work recently).
>
> Currently, I am working on the issue of flexible length array as the last
> field of the structure.
>
> In order to fix it correctly, I have the following question:
>
>
> > On Feb 26, 2021, at 3:42 PM, Kees Cook <keesc...@chromium.org> wrote:
> >
> > On Thu, Feb 25, 2021 at 05:56:38PM -0600, Qing Zhao wrote:
> >> Just noticed that you didn’t add -fauto-var-init-approach=D to the command
> >> line.
> >
> > Ah-ha! I didn't realize that was needed; thanks. However, now some of the
> > sources crash in a different way. Here's the reproducer:
> >
> > $ cat poc.i
> > struct a {
> > int b;
> > int array[];
> > };
> > void c() {
> > struct a d;
> > }
> >
>
> For such variable length array as the last field of the structure, static
> initialization is not allowed,
> User needs to explicitly allocate memory and initialize the allocated array
> manually in the source code.
>
> So, if the compiler has to initialize this structure when requested by
> -ftrivial-auto-var-init, I think that
> only the fields before the last fields need to be initialized, Is this the
> correct behavior you expected?
Right, that would be my expectation as well. Putting such a struct on
the stack tends to be nonsensical, but maybe happens if part of a union,
which would get initialized correctly, etc:
union {
struct a {
int b;
int array[];
};
char buf[32];
};
--
Kees Cook
