From: Dave Martin <Dave.Martin@arm.com>
To: Alan Hayward <Alan.Hayward@arm.com>
Cc: "Dave Martin" <dave.martin@foss.arm.com>,
"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
"libc-alpha@sourceware.org" <libc-alpha@sourceware.org>,
"gdb@sourceware.org" <gdb@sourceware.org>,
"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
"Szabolcs Nagy" <Szabolcs.Nagy@arm.com>,
"Catalin Marinas" <Catalin.Marinas@arm.com>,
"Yao Qi" <Yao.Qi@arm.com>, "Will Deacon" <Will.Deacon@arm.com>,
"Richard Sandiford" <Richard.Sandiford@arm.com>, nd <nd@arm.com>,
"Alex Bennée" <alex.bennee@linaro.org>,
"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 14/28] arm64/sve: Backend logic for setting the vector length
Date: Thu, 21 Sep 2017 11:19:00 -0000 [thread overview]
Message-ID: <20170921111937.GA17434@e103592.cambridge.arm.com> (raw)
In-Reply-To: <E82895B2-3F95-4A54-8703-D654221F8CBA@arm.com>
On Wed, Sep 20, 2017 at 06:08:21PM +0000, Alan Hayward wrote:
>
> > On 20 Sep 2017, at 12:09, Dave Martin <dave.martin@foss.arm.com> wrote:
[...]
> >> Given, sve_set_vector_length is called when setting the vector length in
> >> PTRACE_SETREGSET, it looks to me like if you set VL to a value that’s not
> >> supported by the hardware, then it’s going to round down to the previous value.
> >> Is that correct? I’m not sure if that’s explained in the docs?
> >
> > Does this cover it?
> >
> > "On success, the calling thread's vector length is changed to the
> > largest value supported by the system that is less than or equal to vl."
> >
> > (For ptrace, I just cross-reference the PR_SVE_SET_VL behaviour, above.)
>
> For ptrace is it worth mentioning user should do a GET after a SET to confirm
> what VL value was actually set?
This seems worth a clarification -- I'd thought this was already
mentioned, but it isn't.
How about:
The caller must make a further GETREGSET call if it needs to know what VL is
actually set by SETREGSET, unless is it known in advance that the requested
VL is supported.
[...]
Cheers
---Dave
next prev parent reply other threads:[~2017-09-21 11:19 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1504198860-12951-1-git-send-email-Dave.Martin@arm.com>
2017-08-31 17:01 ` [PATCH v2 09/28] arm64/sve: Signal frame and context structure definition Dave Martin
2017-09-13 13:36 ` Catalin Marinas
2017-09-13 21:33 ` Dave Martin
2017-08-31 17:02 ` [PATCH v2 19/28] arm64/sve: ptrace and ELF coredump support Dave Martin
2017-09-06 16:22 ` Okamoto, Takayuki
[not found] ` <20170906181634.GF6321@e103592.cambridge.arm.com>
2017-09-07 5:11 ` Okamoto, Takayuki
2017-09-08 13:11 ` Dave Martin
2017-09-14 12:57 ` Alex Bennée
2017-09-28 14:57 ` Dave Martin
2017-09-29 12:46 ` Dave Martin
2017-08-31 17:09 ` [PATCH v2 14/28] arm64/sve: Backend logic for setting the vector length Dave Martin
2017-09-13 17:29 ` Catalin Marinas
2017-09-13 19:06 ` Dave Martin
2017-09-13 22:11 ` Catalin Marinas
2017-10-05 16:42 ` Dave Martin
2017-10-05 16:53 ` Catalin Marinas
2017-10-05 17:04 ` Dave Martin
2017-09-20 11:00 ` Alan Hayward
[not found] ` <20170920110902.GG24231@e103592.cambridge.arm.com>
2017-09-20 18:08 ` Alan Hayward
2017-09-21 11:19 ` Dave Martin [this message]
2017-09-21 11:57 ` Alan Hayward
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