Re: [PATCH] x86, crypto: Check if gas supports CRC32

[Mathias Krause]

On Wed, Jul 30, 2014 at 06:47:01PM +0200, Borislav Petkov wrote:
> Building current kernel with some old toolchain (gcc 4.1.2 and gas 2.17)
> chokes with:
> 
> arch/x86/crypto/crc32c-pcl-intel-asm_64.S: Assembler messages:
> arch/x86/crypto/crc32c-pcl-intel-asm_64.S:128: Error: no such instruction: `crc32b %bl,%r8d'
> arch/x86/crypto/crc32c-pcl-intel-asm_64.S:204: Error: no such instruction: `crc32q -i*8(%rcx),%r8'
> ...
> 
> due to the fact that gas doesn't know the CRC32 instruction. Check that
> before building.
> 
> Cc: linux-crypto@xxxxxxxxxxxxxxx
> Signed-off-by: Borislav Petkov <bp@xxxxxxx>
> ---
> 
> So this is one possibility to address this. Code already
> has the ifdeffery around crc_pcl() which is implemented in
> crc32c-pcl-intel-asm_64.S so we can piggyback on that and not build that
> file if gas doesn't know CRC32.
> 
> If no CRC32 support, it still builds fine silently, however it would be
> better to probably say that due to old toolchain, kernel doesn't include
> fast CRC32 stuff in crc32c-intel.ko.
> 
> Hmmm.
> 
> 
>  arch/x86/crypto/Makefile            |  8 +++++++-
>  arch/x86/crypto/crc32c-intel_glue.c |  7 ++++---
>  scripts/gas-can-do-crc32.sh         | 12 ++++++++++++
>  3 files changed, 23 insertions(+), 4 deletions(-)
>  create mode 100755 scripts/gas-can-do-crc32.sh
> 
> diff --git a/arch/x86/crypto/Makefile b/arch/x86/crypto/Makefile
> index 61d6e281898b..707bf7ecb903 100644
> --- a/arch/x86/crypto/Makefile
> +++ b/arch/x86/crypto/Makefile
> @@ -83,7 +83,13 @@ ifeq ($(avx2_supported),yes)
>  sha1-ssse3-y += sha1_avx2_x86_64_asm.o
>  endif
>  crc32c-intel-y := crc32c-intel_glue.o
> -crc32c-intel-$(CONFIG_64BIT) += crc32c-pcl-intel-asm_64.o
> +
> +gas_can_crc32 := $(srctree)/scripts/gas-can-do-crc32.sh
> +CONFIG_GAS_SUPPORTS_CRC32=$(shell $(CONFIG_SHELL) $(gas_can_crc32) $(AS))
> +

This looks too complicated. We do have as-instr for exactly those kind
of tests. And, in fact, looking at arch/x86/Makefile we already have one
for crc32:

  asinstr += $(call as-instr,crc32l %eax$(comma)%eax,-DCONFIG_AS_CRC32=1)

So you can just used CONFIG_AS_CRC32 for your tests and drop the shell
script.

> +ifdef CONFIG_64BIT
> +crc32c-intel-$(CONFIG_GAS_SUPPORTS_CRC32) += crc32c-pcl-intel-asm_64.o
> +endif

s/CONFIG_GAS_SUPPORTS_CRC32/CONFIG_AS_CRC32/ here and for all further
uses.

>  crc32-pclmul-y := crc32-pclmul_asm.o crc32-pclmul_glue.o
>  sha256-ssse3-y := sha256-ssse3-asm.o sha256-avx-asm.o sha256-avx2-asm.o sha256_ssse3_glue.o
>  sha512-ssse3-y := sha512-ssse3-asm.o sha512-avx-asm.o sha512-avx2-asm.o sha512_ssse3_glue.o
> diff --git a/arch/x86/crypto/crc32c-intel_glue.c b/arch/x86/crypto/crc32c-intel_glue.c
> index 6812ad98355c..4ce8e2db2984 100644
> --- a/arch/x86/crypto/crc32c-intel_glue.c
> +++ b/arch/x86/crypto/crc32c-intel_glue.c
> @@ -46,7 +46,7 @@
>  #define REX_PRE
>  #endif
>  
> -#ifdef CONFIG_X86_64
> +#if defined(CONFIG_X86_64) && defined(CONFIG_GAS_SUPPORTS_CRC32)
>  /*
>   * use carryless multiply version of crc32c when buffer
>   * size is >= 512 (when eager fpu is enabled) or
> @@ -181,7 +181,7 @@ static int crc32c_intel_cra_init(struct crypto_tfm *tfm)
>  	return 0;
>  }
>  
> -#ifdef CONFIG_X86_64
> +#if defined(CONFIG_X86_64) && defined(CONFIG_GAS_SUPPORTS_CRC32)
>  static int crc32c_pcl_intel_update(struct shash_desc *desc, const u8 *data,
>  			       unsigned int len)
>  {
> @@ -257,7 +257,8 @@ static int __init crc32c_intel_mod_init(void)
>  {
>  	if (!x86_match_cpu(crc32c_cpu_id))
>  		return -ENODEV;
> -#ifdef CONFIG_X86_64
> +
> +#if defined(CONFIG_X86_64) && defined(CONFIG_GAS_SUPPORTS_CRC32)
>  	if (cpu_has_pclmulqdq) {
>  		alg.update = crc32c_pcl_intel_update;
>  		alg.finup = crc32c_pcl_intel_finup;
> diff --git a/scripts/gas-can-do-crc32.sh b/scripts/gas-can-do-crc32.sh
> new file mode 100755
> index 000000000000..88ff476bd3cc
> --- /dev/null
> +++ b/scripts/gas-can-do-crc32.sh
> @@ -0,0 +1,12 @@
> +#!/bin/sh
> +
> +TMP=$(mktemp)
> +
> +echo "crc32 %rax,%rbx" | $* --warn - -o $TMP 2>/dev/null
> +if [ "$?" -eq "0" ]; then
> +	echo y
> +else
> +	echo n
> +fi
> +
> +rm -f $TMP
> -- 
> 2.0.0
> 

Regards,
Mathias
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