linux-kernel - Re: [PATCH v2] ELF: supply userspace with available page shifts (AT_PAGE_SHIFT

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Message-ID: <87lea4czki.fsf@oldenburg.str.redhat.com>
Date:   Fri, 08 Dec 2023 19:35:25 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-api@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2] ELF: supply userspace with available page shifts
 (AT_PAGE_SHIFT_MASK)

* Kees Cook:

> I significantly prefer APIs not being arch-specific, so I'd prefer we
> always include AT_PAGE_SHIFT_MASK. For an architecture that doesn't
> define its own ARCH_AT_PAGE_SHIFT_MASK, it's not _inaccurate_ to report
> 1 << PAGE_SHIFT, but it might be incomplete.

The downside is that as an application programmer, I have to go and
chase for the information the legacy way if I encounter
getauxval(AT_PAGE_SHIFT_MASK) == getpagesize() for a longer time
because the interface does not signal the absence of any extended
page sizes.

Thanks,
Florian