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

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Message-ID: <8734wehvto.fsf@oldenburg.str.redhat.com>
Date:   Thu, 07 Dec 2023 16:32:51 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        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)

* Alexey Dobriyan:

> On Wed, Dec 06, 2023 at 12:47:27PM -0800, Kees Cook wrote:
>> On Tue, Dec 05, 2023 at 07:01:34PM +0300, Alexey Dobriyan wrote:
>> > Report available page shifts in arch independent manner, so that
>> > userspace developers won't have to parse /proc/cpuinfo hunting
>> > for arch specific strings:
>> > 
>> > Note!
>> > 
>> > This is strictly for userspace, if some page size is shutdown due
>> > to kernel command line option or CPU bug workaround, than is must not
>> > be reported in aux vector!
>> 
>> Given Florian in CC, I assume this is something glibc would like to be
>> using? Please mention this in the commit log.
>
> glibc can use it. Main user is libhugetlbfs, I guess:
>
> 	https://github.com/libhugetlbfs/libhugetlbfs/blob/master/hugeutils.c#L915
>
> Loop inside getauxval() can run faster than opendir().

Is libhugetlbfs still maintained?  Last commit was three years ago?

Thanks,
Florian