Re: [PATCH v2] [v2] crypto: aes-generic - fix aes-generic regression on powerpc

[Ard Biesheuvel]

On 15 January 2018 at 16:07, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> My last bugfix added -Os on the command line, which unfortunately caused
> a build regression on powerpc in some configurations.
>
> I've done some more analysis of the original problem and found slightly
> different workaround that avoids this regression and also results in
> better performance on gcc-7.0: -fcode-hoisting is an optimization step
> that got added in gcc-7 and that for all gcc-7 versions causes worse
> performance.
>
> This disables -fcode-hoisting on all compilers that understand the option.
> For gcc-7.1 and 7.2 I found the same performance as my previous patch
> (using -Os), in gcc-7.0 it was even better. On gcc-8 I could see no
> change in performance from this patch. In theory, code hoisting should
> not be able make things better for the AES cipher, so leaving it
> disabled for gcc-8 only serves to simplify the Makefile change.
>
> Reported-by: kbuild test robot <fengguang.wu@xxxxxxxxx>
> Link: https://www.mail-archive.com/linux-crypto@xxxxxxxxxxxxxxx/msg30418.html
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83651
> Fixes: 148b974deea9 ("crypto: aes-generic - build with -Os on gcc-7+")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

Acked-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>

> ---
> v2: fix a typo in the Makefile
> ---
>  crypto/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/crypto/Makefile b/crypto/Makefile
> index daa69360e054..cdbc03b35510 100644
> --- a/crypto/Makefile
> +++ b/crypto/Makefile
> @@ -99,7 +99,7 @@ obj-$(CONFIG_CRYPTO_TWOFISH_COMMON) += twofish_common.o
>  obj-$(CONFIG_CRYPTO_SERPENT) += serpent_generic.o
>  CFLAGS_serpent_generic.o := $(call cc-option,-fsched-pressure)  # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79149
>  obj-$(CONFIG_CRYPTO_AES) += aes_generic.o
> -CFLAGS_aes_generic.o := $(call cc-ifversion, -ge, 0701, -Os) # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
> +CFLAGS_aes_generic.o := $(call cc-option,-fno-code-hoisting) # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83356
>  obj-$(CONFIG_CRYPTO_AES_TI) += aes_ti.o
>  obj-$(CONFIG_CRYPTO_CAMELLIA) += camellia_generic.o
>  obj-$(CONFIG_CRYPTO_CAST_COMMON) += cast_common.o
> --
> 2.9.0
>