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From:   Florian Weimer <fweimer@redhat.com>
To:     Kees Cook <keescook@chromium.org>
Cc:     Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-api@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH v2] ELF: supply userspace with available page shifts
 (AT_PAGE_SHIFT_MASK)
References: <6b399b86-a478-48b0-92a1-25240a8ede54@p183>
        <87v89dvuxg.fsf@oldenburg.str.redhat.com>
        <1d679805-8a82-44a4-ba14-49d4f28ff597@p183>
        <202312061236.DE847C52AA@keescook>
        <4f5f29d4-9c50-453c-8ad3-03a92fed192e@p183>
        <202312081027.BA44B7B3@keescook>
Date:   Fri, 08 Dec 2023 19:35:25 +0100
In-Reply-To: <202312081027.BA44B7B3@keescook> (Kees Cook's message of "Fri, 8
        Dec 2023 10:29:25 -0800")
Message-ID: <87lea4czki.fsf@oldenburg.str.redhat.com>
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* 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