[PATCH net-next v8 01/28] ARM: makefile: use ARMv3M mode for RiscPC

Jason A. Donenfeld
2018-10-18T14:57:39Z

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@zx2c4.com>
---

Notes:
This commit has been submitted to the proper ARM tree and is working its
way upstream. It's included in this series here so that kbuild 0-day bot
doesn't get too nervous about RiscPC, but is already entering the tree
through arm-next.

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)
--
2.19.1