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From: Mark Rutland <mark.rutland@arm.com>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: linux-arm-kernel@lists.infradead.org,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: CONFIG_ARCH_SUPPORTS_INT128 for AArch64
Date: Tue, 31 Oct 2017 10:43:32 +0000	[thread overview]
Message-ID: <20171031104332.gqpd6icvrxt2uj4c@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <CAHmME9q3=k2fJMi4Zy6d=ewj-P=sRhB8c_MjSJAMbKkopThi1w@mail.gmail.com>

On Tue, Oct 31, 2017 at 11:17:52AM +0100, Jason A. Donenfeld wrote:
> Hi folks,
> 
> Older versions of gcc are horrible for int128_t on aarch64, emitting a
> __multi3 call, which is slow and defeats the purpose. However, more
> recent versions of gcc (since 5, IIRC), do the right thing and produce
> the proper inlined instructions.
> 
> Do we have the infrastructure available to test for this, and
> conditionally set CONFIG_ARCH_SUPPORTS_INT128 if we do?

Judging by Documentation/kbuild/makefiles.txt, we could do something
like the below in the arm64 Makefile:

cflags-y += $(call cc-ifversion, -ge, 0500, -DCONFIG_ARCH_SUPPORTS_INT128)

Note that I havent tested this at all.

Thanks,

WARNING: multiple messages have this Message-ID (diff)
From: mark.rutland@arm.com (Mark Rutland)
To: linux-arm-kernel@lists.infradead.org
Subject: CONFIG_ARCH_SUPPORTS_INT128 for AArch64
Date: Tue, 31 Oct 2017 10:43:32 +0000	[thread overview]
Message-ID: <20171031104332.gqpd6icvrxt2uj4c@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <CAHmME9q3=k2fJMi4Zy6d=ewj-P=sRhB8c_MjSJAMbKkopThi1w@mail.gmail.com>

On Tue, Oct 31, 2017 at 11:17:52AM +0100, Jason A. Donenfeld wrote:
> Hi folks,
> 
> Older versions of gcc are horrible for int128_t on aarch64, emitting a
> __multi3 call, which is slow and defeats the purpose. However, more
> recent versions of gcc (since 5, IIRC), do the right thing and produce
> the proper inlined instructions.
> 
> Do we have the infrastructure available to test for this, and
> conditionally set CONFIG_ARCH_SUPPORTS_INT128 if we do?

Judging by Documentation/kbuild/makefiles.txt, we could do something
like the below in the arm64 Makefile:

cflags-y += $(call cc-ifversion, -ge, 0500, -DCONFIG_ARCH_SUPPORTS_INT128)

Note that I havent tested this at all.

Thanks,

  reply	other threads:[~2017-10-31 10:43 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-31 10:17 CONFIG_ARCH_SUPPORTS_INT128 for AArch64 Jason A. Donenfeld
2017-10-31 10:17 ` Jason A. Donenfeld
2017-10-31 10:43 ` Mark Rutland [this message]
2017-10-31 10:43   ` Mark Rutland
2017-10-31 11:17   ` Jason A. Donenfeld
2017-10-31 11:17     ` Jason A. Donenfeld
2017-10-31 11:43     ` [PATCH] arm64: support __int128 on gcc 5+ Jason A. Donenfeld
2017-10-31 11:43       ` Jason A. Donenfeld
2017-10-31 11:51       ` Will Deacon
2017-10-31 11:51         ` Will Deacon
2017-10-31 11:57         ` Jason A. Donenfeld
2017-10-31 11:57           ` Jason A. Donenfeld
2017-10-31 12:17           ` Will Deacon
2017-10-31 12:17             ` Will Deacon
2017-10-31 12:18             ` Jason A. Donenfeld
2017-10-31 12:18               ` Jason A. Donenfeld
2017-11-02 13:47       ` Will Deacon
2017-11-02 13:47         ` Will Deacon
2017-11-02 17:43         ` [PATCH v2] " Jason A. Donenfeld
2017-11-02 17:43           ` Jason A. Donenfeld
2017-11-03 13:42           ` Will Deacon
2017-11-03 13:42             ` Will Deacon
2017-11-03 14:02             ` Ard Biesheuvel
2017-11-03 14:02               ` Ard Biesheuvel
2017-11-03 14:14             ` Jason A. Donenfeld
2017-11-03 14:14               ` Jason A. Donenfeld
2017-11-03 14:18               ` [PATCH v3] " Jason A. Donenfeld
2017-11-03 14:18                 ` Jason A. Donenfeld
2017-11-06  9:31                 ` [PATCH v4] " Jason A. Donenfeld
2017-11-06  9:31                   ` Jason A. Donenfeld
2017-11-06 15:59                   ` Catalin Marinas
2017-11-06 15:59                     ` Catalin Marinas
2017-11-06 16:14                     ` Catalin Marinas
2017-11-06 16:14                       ` Catalin Marinas
     [not found]                       ` <CAHmME9p+ef-+fmdiO15LU7X3Sr-CDyngpPwKZN2FqOQmZNjLtg@mail.gmail.com>
2017-11-06 16:55                         ` Ard Biesheuvel
2017-11-06 16:55                           ` Ard Biesheuvel
2017-11-06 23:58                           ` [PATCH v5] " Jason A. Donenfeld
2017-11-06 23:58                             ` Jason A. Donenfeld
2017-11-07  0:01                           ` [PATCH v4] " Jason A. Donenfeld
2017-11-07  0:01                             ` Jason A. Donenfeld
2017-11-07  2:13                     ` Will Deacon
2017-11-07  2:13                       ` Will Deacon
2017-11-07  2:16                       ` Jason A. Donenfeld
2017-11-07  2:16                         ` Jason A. Donenfeld
2017-11-02 20:24         ` [PATCH] " Jason A. Donenfeld
2017-11-02 20:24           ` Jason A. Donenfeld

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