Re: [Xen-devel] [PATCH] xen/arm: optee: fix compilation with GCC 4.8

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 20 Jun 2019, Volodymyr Babchuk wrote:
> GCC 4.8 is unable to see that variables guest_pg, guest_data and
> xen_data will be always initialized before access, so we need to
> initialize them earlier.
> 
> Suggested-by: Stefano Stabellini <stefanos@xxxxxxxxxx>
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>

I verified that it works correctly. Thanks for the patch!  (Julien, I
didn't commit it yet to give you a chance to give it a look too.)

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
>  xen/arch/arm/tee/optee.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
> index 14381d6b2d..5526875e6f 100644
> --- a/xen/arch/arm/tee/optee.c
> +++ b/xen/arch/arm/tee/optee.c
> @@ -717,6 +717,19 @@ static int translate_noncontig(struct optee_domain *ctx,
>      gfn = gaddr_to_gfn(param->u.tmem.buf_ptr &
>                         ~(OPTEE_MSG_NONCONTIG_PAGE_SIZE - 1));
>  
> +    /*
> +     * We are initializing guest_pg, guest_data and xen_data with NULL
> +     * to make GCC 4.8 happy, as it can't infer that those variables
> +     * will be initialized with correct values in the loop below.
> +     *
> +     * This silences old GCC, but can lead to NULL dereference, in
> +     * case of programmer's mistake. To minimize chance of this, we
> +     * are initializing those variables there, instead of doing this
> +     * at beginning of the function.
> +     */
> +    guest_pg = NULL;
> +    xen_data = NULL;
> +    guest_data = NULL;
>      while ( pg_count )
>      {
>          struct page_info *page;
> -- 
> 2.21.0
> 

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