Re: [PATCH v2] kasan: don't emit builtin calls when sanitization is off

[Andrey Ryabinin]

On 01/23/2018 05:20 AM, Andrew Morton wrote:
> On Fri, 19 Jan 2018 18:58:12 +0100 Andrey Konovalov <andreyknvl@xxxxxxxxxx> wrote:
> 
>> With KASAN enabled the kernel has two different memset() functions, one
>> with KASAN checks (memset) and one without (__memset). KASAN uses some
>> macro tricks to use the proper version where required. For example memset()
>> calls in mm/slub.c are without KASAN checks, since they operate on poisoned
>> slab object metadata.
>>
>> The issue is that clang emits memset() calls even when there is no memset()
>> in the source code. They get linked with improper memset() implementation
>> and the kernel fails to boot due to a huge amount of KASAN reports during
>> early boot stages.
>>
>> The solution is to add -fno-builtin flag for files with KASAN_SANITIZE := n
>> marker.
> 
> This clashes somewhat with Arnd's asan-rework-kconfig-settings.patch. 
> Could you two please put heads together and decide what we want for a
> final result?
> 
> Meanwhile I'll "fix" the reject with
> 
> +ifdef CONFIG_KASAN_EXTRA
>  CFLAGS_KASAN += $(call cc-option, -fsanitize-address-use-after-scope)
> +endif
> 

Looks correct.