linux-kernel - [PATCH] ARM: makefile: use ARMv3M mode for RiscPC

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Message-Id: <20181002132026.14931-1-Jason@zx2c4.com>
Date:   Tue,  2 Oct 2018 15:20:26 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        arm@...nel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH] ARM: makefile: use ARMv3M mode for RiscPC

The purpose of CONFIG_CPU_32v3 is to avoid ldrh/strh on the RiscPC,
which is pretty much an ARMv4 device, except its bus will choke on the
half-words. The way to make the C compiler not output ldrh/strh is with
-march=armv3, which doesn't support them in the ISA. However, this
prevents certain cryptography code from working that uses instructions
like umull. Fortunately there's also -march=armv3m that does support
those, making it possible to continue assembling optimized cryptography
routines for our beloved RiscPC.

Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Russell King <linux@...linux.org.uk>
Cc: Arnd Bergmann <arnd@...db.de>
---
 arch/arm/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index d1516f85f25d..7fd4bcaf0721 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -74,7 +74,7 @@ endif
 arch-$(CONFIG_CPU_32v5)		=-D__LINUX_ARM_ARCH__=5 $(call cc-option,-march=armv5te,-march=armv4t)
 arch-$(CONFIG_CPU_32v4T)	=-D__LINUX_ARM_ARCH__=4 -march=armv4t
 arch-$(CONFIG_CPU_32v4)		=-D__LINUX_ARM_ARCH__=4 -march=armv4
-arch-$(CONFIG_CPU_32v3)		=-D__LINUX_ARM_ARCH__=3 -march=armv3
+arch-$(CONFIG_CPU_32v3)		=-D__LINUX_ARM_ARCH__=3 -march=armv3m
 
 # Evaluate arch cc-option calls now
 arch-y := $(arch-y)
-- 
2.19.0