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Date: Thu, 12 Nov 2020 09:42:24 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Jian Cai <jiancai@...gle.com>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>,
Manoj Gupta <manojgupta@...gle.com>,
Luis Lozano <llozano@...gle.com>,
clang-built-linux <clang-built-linux@...glegroups.com>,
Russell King <linux@...linux.org.uk>,
Nathan Chancellor <natechancellor@...il.com>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] Make iwmmxt.S support Clang's integrated assembler
On Sat, 7 Nov 2020 at 01:11, Jian Cai <jiancai@...gle.com> wrote:
>
> This patch replaces 6 IWMMXT instructions Clang's integrated assembler
> does not support in iwmmxt.S using macros, while making sure GNU
> assembler still emit the same instructions. This should be easier than
> providing full IWMMXT support in Clang.
>
> "Intel Wireless MMX Technology - Developer Guide - August, 2002" should
> be referenced for the encoding schemes of these extensions.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/975
>
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> Signed-off-by: Jian Cai <jiancai@...gle.com>
For the change itself,
Acked-by: Ard Biesheuvel <ardb@...nel.org>
Although I must admit I am still on the fence when it comes to the
policy around rewriting perfectly valid code like this to accommodate
a toolchain that nobody is likely to use to build the code in
question.
Perhaps we should at least add some rationale to the commit log why
Clang's integrated assembler is something we should care about? I take
it this is not about diagnostics or CFI but simply about avoiding the
need to carry cross-binutils in the first place?
> ---
> arch/arm/kernel/iwmmxt.S | 89 ++++++++++++++++++++--------------------
> arch/arm/kernel/iwmmxt.h | 47 +++++++++++++++++++++
> 2 files changed, 92 insertions(+), 44 deletions(-)
> create mode 100644 arch/arm/kernel/iwmmxt.h
>
> diff --git a/arch/arm/kernel/iwmmxt.S b/arch/arm/kernel/iwmmxt.S
> index 0dcae787b004..d2b4ac06e4ed 100644
> --- a/arch/arm/kernel/iwmmxt.S
> +++ b/arch/arm/kernel/iwmmxt.S
> @@ -16,6 +16,7 @@
> #include <asm/thread_info.h>
> #include <asm/asm-offsets.h>
> #include <asm/assembler.h>
> +#include "iwmmxt.h"
>
> #if defined(CONFIG_CPU_PJ4) || defined(CONFIG_CPU_PJ4B)
> #define PJ4(code...) code
> @@ -113,33 +114,33 @@ concan_save:
>
> concan_dump:
>
> - wstrw wCSSF, [r1, #MMX_WCSSF]
> - wstrw wCASF, [r1, #MMX_WCASF]
> - wstrw wCGR0, [r1, #MMX_WCGR0]
> - wstrw wCGR1, [r1, #MMX_WCGR1]
> - wstrw wCGR2, [r1, #MMX_WCGR2]
> - wstrw wCGR3, [r1, #MMX_WCGR3]
> + wstrw wCSSF, r1, MMX_WCSSF
> + wstrw wCASF, r1, MMX_WCASF
> + wstrw wCGR0, r1, MMX_WCGR0
> + wstrw wCGR1, r1, MMX_WCGR1
> + wstrw wCGR2, r1, MMX_WCGR2
> + wstrw wCGR3, r1, MMX_WCGR3
>
> 1: @ MUP? wRn
> tst r2, #0x2
> beq 2f
>
> - wstrd wR0, [r1, #MMX_WR0]
> - wstrd wR1, [r1, #MMX_WR1]
> - wstrd wR2, [r1, #MMX_WR2]
> - wstrd wR3, [r1, #MMX_WR3]
> - wstrd wR4, [r1, #MMX_WR4]
> - wstrd wR5, [r1, #MMX_WR5]
> - wstrd wR6, [r1, #MMX_WR6]
> - wstrd wR7, [r1, #MMX_WR7]
> - wstrd wR8, [r1, #MMX_WR8]
> - wstrd wR9, [r1, #MMX_WR9]
> - wstrd wR10, [r1, #MMX_WR10]
> - wstrd wR11, [r1, #MMX_WR11]
> - wstrd wR12, [r1, #MMX_WR12]
> - wstrd wR13, [r1, #MMX_WR13]
> - wstrd wR14, [r1, #MMX_WR14]
> - wstrd wR15, [r1, #MMX_WR15]
> + wstrd wR0, r1, MMX_WR0
> + wstrd wR1, r1, MMX_WR1
> + wstrd wR2, r1, MMX_WR2
> + wstrd wR3, r1, MMX_WR3
> + wstrd wR4, r1, MMX_WR4
> + wstrd wR5, r1, MMX_WR5
> + wstrd wR6, r1, MMX_WR6
> + wstrd wR7, r1, MMX_WR7
> + wstrd wR8, r1, MMX_WR8
> + wstrd wR9, r1, MMX_WR9
> + wstrd wR10, r1, MMX_WR10
> + wstrd wR11, r1, MMX_WR11
> + wstrd wR12, r1, MMX_WR12
> + wstrd wR13, r1, MMX_WR13
> + wstrd wR14, r1, MMX_WR14
> + wstrd wR15, r1, MMX_WR15
>
> 2: teq r0, #0 @ anything to load?
> reteq lr @ if not, return
> @@ -147,30 +148,30 @@ concan_dump:
> concan_load:
>
> @ Load wRn
> - wldrd wR0, [r0, #MMX_WR0]
> - wldrd wR1, [r0, #MMX_WR1]
> - wldrd wR2, [r0, #MMX_WR2]
> - wldrd wR3, [r0, #MMX_WR3]
> - wldrd wR4, [r0, #MMX_WR4]
> - wldrd wR5, [r0, #MMX_WR5]
> - wldrd wR6, [r0, #MMX_WR6]
> - wldrd wR7, [r0, #MMX_WR7]
> - wldrd wR8, [r0, #MMX_WR8]
> - wldrd wR9, [r0, #MMX_WR9]
> - wldrd wR10, [r0, #MMX_WR10]
> - wldrd wR11, [r0, #MMX_WR11]
> - wldrd wR12, [r0, #MMX_WR12]
> - wldrd wR13, [r0, #MMX_WR13]
> - wldrd wR14, [r0, #MMX_WR14]
> - wldrd wR15, [r0, #MMX_WR15]
> + wldrd wR0, r0, MMX_WR0
> + wldrd wR1, r0, MMX_WR1
> + wldrd wR2, r0, MMX_WR2
> + wldrd wR3, r0, MMX_WR3
> + wldrd wR4, r0, MMX_WR4
> + wldrd wR5, r0, MMX_WR5
> + wldrd wR6, r0, MMX_WR6
> + wldrd wR7, r0, MMX_WR7
> + wldrd wR8, r0, MMX_WR8
> + wldrd wR9, r0, MMX_WR9
> + wldrd wR10, r0, MMX_WR10
> + wldrd wR11, r0, MMX_WR11
> + wldrd wR12, r0, MMX_WR12
> + wldrd wR13, r0, MMX_WR13
> + wldrd wR14, r0, MMX_WR14
> + wldrd wR15, r0, MMX_WR15
>
> @ Load wCx
> - wldrw wCSSF, [r0, #MMX_WCSSF]
> - wldrw wCASF, [r0, #MMX_WCASF]
> - wldrw wCGR0, [r0, #MMX_WCGR0]
> - wldrw wCGR1, [r0, #MMX_WCGR1]
> - wldrw wCGR2, [r0, #MMX_WCGR2]
> - wldrw wCGR3, [r0, #MMX_WCGR3]
> + wldrw wCSSF, r0, MMX_WCSSF
> + wldrw wCASF, r0, MMX_WCASF
> + wldrw wCGR0, r0, MMX_WCGR0
> + wldrw wCGR1, r0, MMX_WCGR1
> + wldrw wCGR2, r0, MMX_WCGR2
> + wldrw wCGR3, r0, MMX_WCGR3
>
> @ clear CUP/MUP (only if r1 != 0)
> teq r1, #0
> diff --git a/arch/arm/kernel/iwmmxt.h b/arch/arm/kernel/iwmmxt.h
> new file mode 100644
> index 000000000000..fb627286f5bb
> --- /dev/null
> +++ b/arch/arm/kernel/iwmmxt.h
> @@ -0,0 +1,47 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef __IWMMXT_H__
> +#define __IWMMXT_H__
> +
> +.irp b, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15
> +.set .LwR\b, \b
> +.set .Lr\b, \b
> +.endr
> +
> +.set .LwCSSF, 0x2
> +.set .LwCASF, 0x3
> +.set .LwCGR0, 0x8
> +.set .LwCGR1, 0x9
> +.set .LwCGR2, 0xa
> +.set .LwCGR3, 0xb
> +
> +.macro wldrd, reg:req, base:req, offset:req
> +.inst 0xedd00100 | (.L\reg << 12) | (.L\base << 16) | (\offset >> 2)
> +.endm
> +
> +.macro wldrw, reg:req, base:req, offset:req
> +.inst 0xfd900100 | (.L\reg << 12) | (.L\base << 16) | (\offset >> 2)
> +.endm
> +
> +.macro wstrd, reg:req, base:req, offset:req
> +.inst 0xedc00100 | (.L\reg << 12) | (.L\base << 16) | (\offset >> 2)
> +.endm
> +
> +.macro wstrw, reg:req, base:req, offset:req
> +.inst 0xfd800100 | (.L\reg << 12) | (.L\base << 16) | (\offset >> 2)
> +.endm
> +
> +#ifdef __clang__
> +
> +#define wCon c1
> +
> +.macro tmrc, dest:req, control:req
> +mrc p1, 0, \dest, \control, c0, 0
> +.endm
> +
> +.macro tmcr, control:req, src:req
> +mcr p1, 0, \src, \control, c0, 0
> +.endm
> +#endif
> +
> +#endif
> --
> 2.29.1.341.ge80a0c044ae-goog
>
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