Re: [PATCH v3 1/3] powerpc/mm: prepare kernel for KAsan on PPC32

On Sat, Jan 12, 2019 at 12:16 PM Christophe Leroy
[off-list ref] wrote:
>
> In kernel/cputable.c, explicitly use memcpy() in order
> to allow GCC to replace it with __memcpy() when KASAN is
> selected.
>
> Since commit 400c47d81ca38 ("powerpc32: memset: only use dcbz once cache is
> enabled"), memset() can be used before activation of the cache,
> so no need to use memset_io() for zeroing the BSS.
>
> Signed-off-by: Christophe Leroy [off-list ref]
> ---
>  arch/powerpc/kernel/cputable.c | 4 ++--
>  arch/powerpc/kernel/setup_32.c | 6 ++----
>  2 files changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/kernel/cputable.c
b/arch/powerpc/kernel/cputable.c
> index 1eab54bc6ee9..84814c8d1bcb 100644
> --- a/arch/powerpc/kernel/cputable.c
> +++ b/arch/powerpc/kernel/cputable.c
> @@ -2147,7 +2147,7 @@ void __init set_cur_cpu_spec(struct cpu_spec *s)
>         struct cpu_spec *t = &the_cpu_spec;
>
>         t = PTRRELOC(t);
> -       *t = *s;
> +       memcpy(t, s, sizeof(*t));

Hi Christophe,

I understand why you are doing this, but this looks a bit fragile and
non-scalable. This may not work with the next version of compiler,
just different than yours version of compiler, clang, etc.

Does using -ffreestanding and/or -fno-builtin-memcpy (-memset) help?
If it helps, perhaps it makes sense to add these flags to
KASAN_SANITIZE := n files.