Alejandro Colomar (man-pages) <alx.manpa...@gmail.com> wrote:
> Hi,
>
> I don't know if OpenBSD has a different implementation of alloca(3)
> than Linux. In Linux, alloca(3) (a.k.a. __builtin_alloca()) can't
> return NULL, as it can't detect errors.
There are no alloca can return NULL.
> The only way to detect an
> error is to add a handler for SIGSEGV, AFAIK.
Actually, it is worse than that. Massive alloca have been encountered
which reach off the stack. For over 20 years we've been on a mission
to delete alloca in our tree, and these are the last ones that remain,
because other allocators are very difficult to use in this place.
Maybe we should investigate using mmap. Of the 4 cases, 3 are not
too difficult, but the 4th case will be very messy, including unwind
for the 3rd case.
> I found the following code in <lib/libc/gen/exec.c>:
>
> argv = alloca((n + 1) * sizeof(*argv));
> if (argv == NULL) {
> errno = ENOMEM;
> return (-1);
> }
>
> But of course, that NULL should never happen, right?
> As a side note, I think you could encapsulate the code calling
> alloca(3) into a helper macro, to avoid repetition.
I don't see how that would help anything.
> I can prepare a patch if you confirm the bug.
What do you propose to do in your patch?
