crypto: arm - workaround for building with old binutils

Old versions of binutils (before 2.23) do not yet understand the
crypto-neon-fp-armv8 fpu instructions, and an attempt to build these
files results in a build failure:

arch/arm/crypto/aes-ce-core.S:133: Error: selected processor does not support ARM mode `vld1.8 {q10-q11},[ip]!'
arch/arm/crypto/aes-ce-core.S:133: Error: bad instruction `aese.8 q0,q8'
arch/arm/crypto/aes-ce-core.S:133: Error: bad instruction `aesmc.8 q0,q0'
arch/arm/crypto/aes-ce-core.S:133: Error: bad instruction `aese.8 q0,q9'
arch/arm/crypto/aes-ce-core.S:133: Error: bad instruction `aesmc.8 q0,q0'

Since the affected versions are still in widespread use, and this breaks
'allmodconfig' builds, we should try to at least get a successful kernel
build. Unfortunately, I could not come up with a way to make the Kconfig
symbol depend on the binutils version, which would be the nicest solution.

Instead, this patch uses the 'as-instr' Kbuild macro to find out whether
the support is present in the assembler, and otherwise emits a non-fatal
warning indicating which selected modules could not be built.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: http://storage.kernelci.org/next/next-20150410/arm-allmodconfig/build.log
Fixes: 864cbeed ("crypto: arm - add support for SHA1 using ARMv8 Crypto Instructions")
[ard.biesheuvel:
 - omit modules entirely instead of building empty ones if binutils is too old
 - update commit log accordingly]
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

arch/arm/crypto/Makefile

@@ -4,14 +4,25 @@
 
 obj-$(CONFIG_CRYPTO_AES_ARM) += aes-arm.o
 obj-$(CONFIG_CRYPTO_AES_ARM_BS) += aes-arm-bs.o
-obj-$(CONFIG_CRYPTO_AES_ARM_CE) += aes-arm-ce.o
 obj-$(CONFIG_CRYPTO_SHA1_ARM) += sha1-arm.o
 obj-$(CONFIG_CRYPTO_SHA1_ARM_NEON) += sha1-arm-neon.o
 obj-$(CONFIG_CRYPTO_SHA256_ARM) += sha256-arm.o
 obj-$(CONFIG_CRYPTO_SHA512_ARM_NEON) += sha512-arm-neon.o
-obj-$(CONFIG_CRYPTO_SHA1_ARM_CE) += sha1-arm-ce.o
-obj-$(CONFIG_CRYPTO_SHA2_ARM_CE) += sha2-arm-ce.o
-obj-$(CONFIG_CRYPTO_GHASH_ARM_CE) += ghash-arm-ce.o
+
+ce-obj-$(CONFIG_CRYPTO_AES_ARM_CE) += aes-arm-ce.o
+ce-obj-$(CONFIG_CRYPTO_SHA1_ARM_CE) += sha1-arm-ce.o
+ce-obj-$(CONFIG_CRYPTO_SHA2_ARM_CE) += sha2-arm-ce.o
+ce-obj-$(CONFIG_CRYPTO_GHASH_ARM_CE) += ghash-arm-ce.o
+
+ifneq ($(ce-obj-y)$(ce-obj-m),)
+ifeq ($(call as-instr,.fpu crypto-neon-fp-armv8,y,n),y)
+obj-y += $(ce-obj-y)
+obj-m += $(ce-obj-m)
+else
+$(warning These ARMv8 Crypto Extensions modules need binutils 2.23 or higher)
+$(warning $(ce-obj-y) $(ce-obj-m))
+endif
+endif
 
 aes-arm-y	:= aes-armv4.o aes_glue.o
 aes-arm-bs-y	:= aesbs-core.o aesbs-glue.o