Re: [PATCH v2] rust: alloc: satisfy `aligned_alloc` requirements

Danilo Krummrich
2025-02-06T18:04:37Z

On Thu, Feb 06, 2025 at 06:56:38PM +0100, Miguel Ojeda wrote:
> On Sun, Feb 2, 2025 at 12:27 PM Tamir Duberstein <tamird@gmail.com> wrote:
> >
> > requirements of `aligned_alloc`. These requirements may not be enforced
> > on all systems, but they are on macOS. Ensure that alignment is at least
>
> Which requirements? `aligned_alloc` comes from ISO C, and POSIX says
> it is aligned with it; i.e. the change to make it work in macOS seems
> fine, but please see below.
>
> > + // According to `man aligned_alloc`:
> > + //
> > + // aligned_alloc() returns a NULL pointer and sets errno to EINVAL if size is not an
> > + // integral multiple of alignment, or if alignment is not a power of 2 at least as large as
> > + // sizeof(void *).
>
> These requirements seem to come from the macOS man pages, not the
> actual specification. The C one seems required to fail on invalid
> alignments, but is the set of those the ones that macOS mentions? (It
> seems the history of the requirements of that function is convoluted
> and involves at least a DR, and glibc is very lax, more than
> apparently its docs say)

I previously checked man posix_memalign(3) and it says:

ERRORS
EINVAL The alignment argument was not a power of two, or was not a
multiple of sizeof(void *).