From: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
To: Peter Bergner <bergner@linux.ibm.com>,
linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Cc: Nicholas Piggin <npiggin@gmail.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Segher Boessenkool <segher@kernel.crashing.org>,
GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH] uapi/auxvec: Define AT_HWCAP3 and AT_HWCAP4 aux vector, entries
Date: Wed, 4 Oct 2023 08:02:28 -0300 [thread overview]
Message-ID: <bea513ab-9ee2-4808-a490-c7dee5de26a6@linaro.org> (raw)
In-Reply-To: <b4864730-1b12-4dd8-b6e9-85d78dad5e34@linux.ibm.com>
On 03/10/23 19:12, Peter Bergner wrote:
> On 10/3/23 9:08 AM, Adhemerval Zanella Netto wrote:
>> What it is not clear to me is what kind of ABI boundary you are trying to
>> preemptively add support here. The TCB ABI for __builtin_cpu_supports is
>> userland only, so if your intention is just to allow gcc to work on older
>> glibcs, it should be a matter to just reserve the space on tcbhead_t.
>
> Yes, extending tcbhead_t to contain the slots for hwcap3 and hwcap4 are the
> ABI extensions we are interested in, and not something that can be backported
> into a distro point release. Yes, we don't strictly need the AT_HWCAP3 and
> AT_HWCAP4 kernel defines to reserve (and clear) that space in glibc, but....
>
>
>
>> If your intention is to also add support on glibc, it makes more sense to
>> already reserve it. For __builtin_cpu_supports it should work, although
>> for glibc itself some backporting would be required (to correctly showing
>> the bits with LD_SHOW_AUXV).
>
> Our intention is to also add the glibc support too once we have the
> AT_HWCAP3 and AT_HWCAP4 kernel macros defined. 1) Once the defines are
> there, adding the support should be pretty straight forward, so why wait?
> And 2) part of the glibc and compiler support introduces a new symbol
> that is exported by glibc and referenced by the compilers to ensure the
> compilers *never* access the hwcap* fields in the TCB unless the glibc
> supports them. See the symbol __parse_hwcap_and_convert_at_platform used
> for HWCAP/HWCAP2. We'll need a similar one for HWCAP3/HWCAP4 and I'm
> doubtful whether the distros will allow the backport of a patch that
> introduces a new exported symbol from glibc in a distro point release.
Alright, I makes more sense it now. And indeed backporting a __parse_hwcap
for HWCAP3/HWCAP4 will be frown upon.
next prev parent reply other threads:[~2023-10-04 11:02 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-26 22:02 Peter Bergner
2023-09-27 16:03 ` Adhemerval Zanella Netto
2023-10-02 21:19 ` Peter Bergner
2023-10-03 14:08 ` Adhemerval Zanella Netto
2023-10-03 22:12 ` Peter Bergner
2023-10-04 11:02 ` Adhemerval Zanella Netto [this message]
2023-10-17 23:14 ` [PING][PATCH] " Peter Bergner
2023-10-18 16:22 ` Szabolcs Nagy
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