From: Phil Blundell <pb@pbcl.net>
To: Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
Dave P Martin <Dave.Martin@arm.com>,
Andrew Murray <Andrew.Murray@arm.com>
Cc: Catalin Marinas <Catalin.Marinas@arm.com>, nd <nd@arm.com>,
Will Deacon <Will.Deacon@arm.com>,
GNU C Library <libc-alpha@sourceware.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 2/6] arm64: HWCAP: add support for AT_HWCAP2
Date: Fri, 29 Mar 2019 16:57:46 +0000 [thread overview]
Message-ID: <212459f27da12ec266fa1fa970356559a509f76d.camel@pbcl.net> (raw)
In-Reply-To: <83b59b0f-cee7-92d5-2ed2-5300f92d7329@arm.com>
On Fri, 2019-03-29 at 16:44 +0000, Szabolcs Nagy wrote:
> i think hwcap bit 63 is already reserved by glibc
> internally for tls support, it is not clear to me
> if that's still relevant (aarch64 post-dates tls
> support, so this might be historical cruft that can
> be cleaned up), i only see one comment about it:
At the time that bit was invented, it was only set when glibc was built
with TLS support enabled (i.e. USE_TLS defined). It would cause the
dynamic linker to add "tls" as a hwcap subdirectory in its search path, which I guess was useful in the days when TLS-enabled and non-TLS-enabled versions of the same DSO needed to be able to co-exist.
At some later date, I forget when, TLS became mandatory and the USE_TLS
condition went away. The comment seems to be saying that it was
thought necessary to keep the pseudo-hwcap bit set so that any DSOs in
a "tls" subdirectory would still be found. That seems like a debatable proposition even at the time, and even more so today, but I guess it was hard to prove the negative.
Even if aarch64 has always had TLS, in principle there might be some
ancient DSOs lurking in "tls" subdirectories which would no longer be
loaded if you were to stop setting that bit. I'm sure that would be manageable, but equally it doesn't seem that these bits are so scarce that it's worth going to any effort to scavenge old ones.
> i think it's better to use a different bit
> for aarch64 ifunc abi hacks (e.g. 1ULL << 62)
I agree.
p.
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next prev parent reply other threads:[~2019-03-29 16:58 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-21 12:20 [PATCH v2 0/6] Initial support for CVADP Andrew Murray
2019-02-21 12:20 ` [PATCH v2 1/6] arm64: Handle trapped DC CVADP Andrew Murray
2019-02-21 12:39 ` Mark Rutland
2019-02-21 12:20 ` [PATCH v2 2/6] arm64: HWCAP: add support for AT_HWCAP2 Andrew Murray
2019-02-21 18:45 ` Dave P Martin
2019-02-22 10:35 ` Szabolcs Nagy
2019-03-27 15:02 ` Andrew Murray
2019-03-27 15:24 ` Andrew Murray
2019-03-28 11:27 ` Dave Martin
2019-03-29 16:44 ` Szabolcs Nagy
2019-03-29 16:57 ` Phil Blundell [this message]
2019-04-01 8:14 ` Andrew Murray
2019-03-27 14:53 ` Andrew Murray
2019-03-29 15:39 ` Dave Martin
2019-02-21 12:20 ` [PATCH v2 3/6] arm64: HWCAP: encapsulate elf_hwcap Andrew Murray
2019-02-21 18:45 ` Dave P Martin
2019-03-27 14:03 ` Andrew Murray
2019-03-28 11:32 ` Dave Martin
2019-02-21 12:20 ` [PATCH v2 4/6] arm64: Expose DC CVADP to userspace Andrew Murray
2019-02-21 12:20 ` [PATCH v2 5/6] arm64: add CVADP support to the cache maintenance helper Andrew Murray
2019-02-21 12:20 ` [PATCH v2 6/6] arm64: Advertise ARM64_HAS_DCPODP cpu feature Andrew Murray
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