From: Szabolcs Nagy <nsz@port70.net>
To: Siddhesh Poyarekar <siddhesh@sourceware.org>
Cc: Szabolcs Nagy <szabolcs.nagy@arm.com>,
libc-alpha@sourceware.org, nd@arm.com,
adhemerval.zanella@linaro.org
Subject: Re: [PATCH 5/5] aarch64: Allow overriding HWCAP_CPUID feature check using HWCAP_MASK
Date: Sat, 20 May 2017 12:35:00 -0000 [thread overview]
Message-ID: <20170520123541.GL9350@port70.net> (raw)
In-Reply-To: <ee007bd0-0b13-8d7a-7e23-6ab6b4a26977@sourceware.org>
* Siddhesh Poyarekar <siddhesh@sourceware.org> [2017-05-20 09:02:20 +0530]:
> On Saturday 20 May 2017 03:42 AM, Szabolcs Nagy wrote:
> > no oom on aarch64 does not mean there is no problem
> >
> > LD_HWCAP_MASK changes the behaviour of _dl_init_path
> > in elf/ld-load.c which we should understand before
> > the patch is committed (because it implies the
> > env var historically had different semantics than
> > what we assumed).
>
> Ahh, sorry, I just realized that we are talking about different things.
> I thought you were objecting to including the patch until the OOM was fixed.
>
> One may have additional search paths for every hwcap that is set by the
> kernel, so if hwcap_cpuid is set, the linker (and ldconfig) ought to
> search for /usr/lib/hwcap_cpuid for libraries to load as well.
>
> This has an impact only if the target system is configured with
> libraries in that hwcap path, e.g. if someone decides to have additional
> libraries in /usr/lib/<hwcap feature> and that path gets searched only
> if that hwcap feature is enabled. This allows users to ship, say,
> separate set of libraries for avx512 on x86_64 in /usr/lib/avx512_1
> which gets searched before /usr/lib.
>
> So masking out specific bits will disable searching of libraries in
> those paths as well. I hope that answers your question.
ok now i understand it better, my confusion is that
the default seems to be _dl_hwcap_mask == 0, which
would disable the cpuid bit unless one explicitly
set LD_HWCAP_MASK=2048, i thought we wanted the
opposite behaviour (cpuid based dispatch by default,
which can be disabled with explicit setting).
next prev parent reply other threads:[~2017-05-20 12:35 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-18 20:07 [PATCH v2 0/5] aarch64: Allow overriding HWCAP_CPUID feature check Siddhesh Poyarekar
2017-05-18 20:07 ` [PATCH 4/5] Delay initialization of CPU features struct in static binaries Siddhesh Poyarekar
2017-05-25 3:05 ` H.J. Lu
2017-05-18 20:07 ` [PATCH 5/5] aarch64: Allow overriding HWCAP_CPUID feature check using HWCAP_MASK Siddhesh Poyarekar
2017-05-19 9:49 ` Szabolcs Nagy
2017-05-19 17:44 ` Siddhesh Poyarekar
2017-05-19 22:12 ` Szabolcs Nagy
2017-05-20 3:32 ` Siddhesh Poyarekar
2017-05-20 12:35 ` Szabolcs Nagy [this message]
2017-05-20 13:23 ` Siddhesh Poyarekar
2017-05-18 20:07 ` [PATCH 3/5] tunables: Use glibc.tune.hwcap_mask tunable instead of _dl_hwcap_mask Siddhesh Poyarekar
2017-05-22 14:51 ` Adhemerval Zanella
2017-05-18 20:07 ` [PATCH 1/5] tunables: Add hooks to get and update tunables Siddhesh Poyarekar
2017-05-22 14:07 ` Adhemerval Zanella
2017-05-18 20:07 ` [PATCH 2/5] tunables: Add LD_HWCAP_MASK to tunables Siddhesh Poyarekar
2017-05-22 13:20 ` Adhemerval Zanella
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