From: Tulio Magno Quites Machado Filho <tuliom@ascii.art.br>
To: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Nicholas Piggin <npiggin@gmail.com>,
linuxppc-dev@lists.ozlabs.org,
Florian Weimer <fweimer@redhat.com>,
gcc@gcc.gnu.org, libc-alpha@sourceware.org,
Paul E Murphy <murphyp@linux.ibm.com>
Subject: Re: [PATCH v2] powerpc: add documentation for HWCAPs
Date: Fri, 15 Jul 2022 17:17:42 -0300 [thread overview]
Message-ID: <874jziuo49.fsf@linux.ibm.com> (raw)
In-Reply-To: <20220715195951.GA25951@gate.crashing.org>
Segher Boessenkool <segher@kernel.crashing.org> writes:
> That is a usability problem. Can it be fixed, or will that create its
> own compatibility problems? In practice I mean. If it is, the C
> libraries could fix it up, for new programs, and then after a while the
> kernel can do the sane thing?
>
> How big is the problem, anyway? Is it only 2.05, or also 2.04, 2.03?
PPC_FEATURE_ARCH_2_05 is the first bit referring to an ISA level.
Before that, AT_HWCAP used to have bits for specific processors, e.g.
PPC_FEATURE_CELL and PPC_FEATURE_POWER4.
Notice that glibc creates its own hwcap-based information that is used by
__builtin_cpu_supports(). In this case bits PPC_FEATURE_ARCH_2_05,
PPC_FEATURE_POWER5_PLUS, PPC_FEATURE_POWER5 and PPC_FEATURE_POWER4 are enabled
whenever if the processor is compatible with the features provided by any of
the previous processors [1].
AT_HWCAP and AT_HWCAP2 are kept intact, though.
[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/powerpc/hwcapinfo.c;h=afde05f86382413ce1f0c38e33c9bdd38d6b7e9d;hb=HEAD#l45
--
Tulio Magno
next prev parent reply other threads:[~2022-07-15 20:17 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-15 1:26 Nicholas Piggin
2022-07-15 14:57 ` Segher Boessenkool
2022-07-15 18:41 ` Tulio Magno Quites Machado Filho
2022-07-15 19:59 ` Segher Boessenkool
2022-07-15 20:17 ` Tulio Magno Quites Machado Filho [this message]
2022-07-20 9:28 ` Nicholas Piggin
2022-07-29 13:02 ` Michael Ellerman
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