On Wed, May 16, 2018 at 11:29:13AM -0400, Rich Felker wrote:

On Wed, May 16, 2018 at 03:20:47PM +0100, Dave Martin wrote:

quoted

There are constraints on defining AT_* auxvec tags that are not
obvious to the casual maintainer of either the global
<uapi/linux/auxvec.h> or the arch-specific headers.  This is likely
to lead to mistakes.  (I certainly fell foul of it...)

For the benefit of future maintainers, this patch collects the
relevant information in one place, documenting how the namespace
needs to be managed, and noting all the values currently in use.

Maintaining a global list may result in some merge conflicts, but
AT_* values are not added frequently.  I'm open to suggestions on
the best approach.

I also assume that values 38 and 39 may have been used for
historical purposes, such as an architecture that is no longer
supported.  If they have definitely never been used for anything,
they could be removed from the "reserved" list.

On the userspace side (elf.h) all the AT_* constants are in one file.
Why don't we just do the same here and eliminate the
arch/*/include/uapi/asm/auxvec.h files and likewise the need to
manually maintain consistency of the comments about reservations?

If there are reasons not to do that, I'm not opposed to this patch
as-is.

I agree, it would be better to merge them.

My concern was that the correct way to get these definitions from
userspace is very unclear, so there may be software out there
including <asm/auxvec.h> directly, which would now lack expected
definitions.

codesearch.debian.net shows no real hits for that, so maybe I'm too
paranoid.

Since <linux/auxvec.h> only contains #defines, it may be enough for arch
<asm/auxvec.h> headers to include <linux/auxvec.h>.

Thoughts?

Cheers
---Dave