Re: [PATCH v2 05/17] vdso: Avoid call to memset() by getrandom

Jason A. Donenfeld
2024-08-28T12:26:27Z

On Wed, Aug 28, 2024 at 2:24 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Wed, Aug 28, 2024, at 11:18, Jason A. Donenfeld wrote:
> > On Tue, Aug 27, 2024 at 05:53:30PM -0500, Segher Boessenkool wrote:
> >> On Tue, Aug 27, 2024 at 11:08:19AM -0700, Eric Biggers wrote:
> >> >
> >> > Is there a compiler flag that could be used to disable the generation of calls
> >> > to memset?
> >>
> >> -fno-tree-loop-distribute-patterns . But, as always, read up on it, see
> >> what it actually does (and how it avoids your problem, and mostly: learn
> >> what the actual problem *was*!)
> >
> > This might help with various loops, but it doesn't help with the matter
> > that this patch fixes, which is struct initialization. I just tried it
> > with the arm64 patch to no avail.
>
> Maybe -ffreestanding can help here? That should cause the vdso to be built
> with the assumption that there is no libc, so it would neither add nor
> remove standard library calls. Not sure if that causes other problems,
> e.g. if the calling conventions are different.

From https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90701:

| You need -ffreestanding but that is documented to emit memset and
memcpy still.