From: will.deacon@arm.com (Will Deacon)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] arm64/cpufeatures: Enforce inline/const properties of cpus_have_const_cap
Date: Thu, 19 Jan 2017 14:37:04 +0000 [thread overview]
Message-ID: <20170119143703.GB31594@arm.com> (raw)
In-Reply-To: <1484740725-24776-1-git-send-email-marc.zyngier@arm.com>
On Wed, Jan 18, 2017 at 11:58:45AM +0000, Marc Zyngier wrote:
> Despite being flagged "inline", cpus_have_const_cap may end-up being
> placed out of line if the compiler decides so. This would be unfortunate,
> as we want to be able to use this function in HYP, where we need to
> be 100% sure of what is mapped there. __always_inline seems to be a
> better choice given the constraint.
>
> Also, be a lot tougher on non-const or out-of-range capability values
> (a non-const cap value shouldn't be used here, and the semantic of an
> OOR value is at best ill defined). In those two case, BUILD_BUG_ON is
> what you get.
>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> arch/arm64/include/asm/cpufeature.h | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index b4989df..4710469 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -105,10 +105,11 @@ static inline bool cpu_have_feature(unsigned int num)
> }
>
> /* System capability check for constant caps */
> -static inline bool cpus_have_const_cap(int num)
> +static __always_inline bool cpus_have_const_cap(int num)
> {
> - if (num >= ARM64_NCAPS)
> - return false;
> + BUILD_BUG_ON(!__builtin_constant_p(num));
> + BUILD_BUG_ON(num >= ARM64_NCAPS);
This gives different behaviour to cpus_have_const_cap when compared to
cpus_have_cap, which I really don't like. What is the current behaviour
if you pass a non-constant num parameter? Does the kernel actually build?
Maybe it's best to spin a separate patch that makes cpus_have_cap and
cpus_have_const_cap both use __always_inline, then we can debate the merit
of the BUILD_BUG_ONs separately.
Will
next prev parent reply other threads:[~2017-01-19 14:37 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-18 11:58 [PATCH] arm64/cpufeatures: Enforce inline/const properties of cpus_have_const_cap Marc Zyngier
2017-01-19 14:37 ` Will Deacon [this message]
2017-01-19 14:42 ` Marc Zyngier
2017-01-19 14:48 ` Will Deacon
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170119143703.GB31594@arm.com \
--to=will.deacon@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.