netdev - Re: [PATCH bpf-next 12/13] bpf: arm64: add JIT support for multi-function programs

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Date:   Mon, 18 Dec 2017 16:29:58 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Edward Cree <ecree@...arflare.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Networking <netdev@...r.kernel.org>, kernel-team@...com
Subject: Re: [PATCH bpf-next 12/13] bpf: arm64: add JIT support for
 multi-function programs

On Fri, Dec 15, 2017 at 2:55 AM, Alexei Starovoitov <ast@...nel.org> wrote:


> +       if (jit_data->ctx.offset) {
> +               ctx = jit_data->ctx;
> +               image_ptr = jit_data->image;
> +               header = jit_data->header;
> +               extra_pass = true;
> +               goto skip_init_ctx;
> +       }
>         memset(&ctx, 0, sizeof(ctx));
>         ctx.prog = prog;

The 'goto' jumps over the 'image_size' initialization

>         prog->bpf_func = (void *)ctx.image;
>         prog->jited = 1;
>         prog->jited_len = image_size;

so we now get a warning here, starting with linux-next-20171218:

arch/arm64/net/bpf_jit_comp.c: In function 'bpf_int_jit_compile':
arch/arm64/net/bpf_jit_comp.c:982:18: error: 'image_size' may be used
uninitialized in this function [-Werror=maybe-uninitialized]

I could not figure out what the code should be doing instead, or if it is
indeed safe and the warning is a false-positive.

        Arnd