Re: [PATCH] lib/ubsan: default UBSAN_ALIGNMENT to not set

[Andrey Ryabinin]

On 12/17/18 6:03 PM, Anders Roxell wrote:
> When booting an allmodconfig kernel, there are a lot of false-positives.
> With a message like this 'UBSAN: Undefined behaviour in...' with a call
> trace that follows.
> 
> Reworked so that when building a allmodconfig kernel that turns
> everything into '=m' or '=y' will turn off UBSAN_ALIGNMENT.
> 
> Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
> Signed-off-by: Anders Roxell <anders.roxell@xxxxxxxxxx>
> ---

Acked-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>


>  lib/Kconfig.ubsan | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/Kconfig.ubsan b/lib/Kconfig.ubsan
> index 98fa559ebd80..a2ae4a8e4fa6 100644
> --- a/lib/Kconfig.ubsan
> +++ b/lib/Kconfig.ubsan
> @@ -27,15 +27,19 @@ config UBSAN_SANITIZE_ALL
>  	  Enabling this option will get kernel image size increased
>  	  significantly.
>  
> -config UBSAN_ALIGNMENT
> -	bool "Enable checking of pointers alignment"
> +config UBSAN_NO_ALIGNMENT
> +	bool "Disable checking of pointers alignment"
>  	depends on UBSAN
> -	default y if !HAVE_EFFICIENT_UNALIGNED_ACCESS
> +	default y if HAVE_EFFICIENT_UNALIGNED_ACCESS
>  	help
> -	  This option enables detection of unaligned memory accesses.
> -	  Enabling this option on architectures that support unaligned
> +	  This option disables the check of unaligned memory accesses.
> +	  This option should be used when building allmodconfig.
> +	  Disabling this option on architectures that support unaligned
>  	  accesses may produce a lot of false positives.
>  
> +config UBSAN_ALIGNMENT
> +	def_bool !UBSAN_NO_ALIGNMENT
> +
>  config TEST_UBSAN
>  	tristate "Module for testing for undefined behavior detection"
>  	depends on m && UBSAN
>