linux-kernel - Re: [PATCH 2/4] sparc: bpf_jit: Move four assignments in bpf_jit

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Date:   Sun, 4 Sep 2016 13:21:01 +1000
From:   Julian Calaby <julian.calaby@...il.com>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:     sparclinux <sparclinux@...r.kernel.org>,
        Adam Buchbinder <adam.buchbinder@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Rabin Vincent <rabin@....in>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors <kernel-janitors@...r.kernel.org>,
        Julia Lawall <julia.lawall@...6.fr>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 2/4] sparc: bpf_jit: Move four assignments in bpf_jit_compile()

Hi Markus,

On Sun, Sep 4, 2016 at 2:38 AM, SF Markus Elfring
<elfring@...rs.sourceforge.net> wrote:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Sat, 3 Sep 2016 17:45:28 +0200
>
> Move the assignments for four local variables a bit at the beginning
> so that they will only be performed if a corresponding memory allocation
> succeeded by this function.
>
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  arch/sparc/net/bpf_jit_comp.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/arch/sparc/net/bpf_jit_comp.c b/arch/sparc/net/bpf_jit_comp.c
> index ced1393..a927470 100644
> --- a/arch/sparc/net/bpf_jit_comp.c
> +++ b/arch/sparc/net/bpf_jit_comp.c
> @@ -362,10 +362,10 @@ do {      *prog++ = BR_OPC | WDISP22(OFF);                \
>
>  void bpf_jit_compile(struct bpf_prog *fp)
>  {
> -       unsigned int cleanup_addr, proglen, oldproglen = 0;
> -       u32 temp[8], *prog, *func, seen = 0, pass;
> -       const struct sock_filter *filter = fp->insns;
> -       int i, flen = fp->len, pc_ret0 = -1;
> +       unsigned int cleanup_addr, proglen, oldproglen;
> +       u32 temp[8], *prog, *func, seen, pass;
> +       const struct sock_filter *filter;
> +       int i, flen = fp->len, pc_ret0;
>         unsigned int *addrs;
>         void *image;
>
> @@ -385,6 +385,10 @@ void bpf_jit_compile(struct bpf_prog *fp)
>         }
>         cleanup_addr = proglen; /* epilogue address */
>         image = NULL;
> +       filter = fp->insns;
> +       oldproglen = 0;
> +       pc_ret0 = -1;
> +       seen = 0;
>         for (pass = 0; pass < 10; pass++) {
>                 u8 seen_or_pass0 = (pass == 0) ? (SEEN_XREG | SEEN_DATAREF | SEEN_MEM) : seen;

This is utterly pointless, why?

If you were moving the assignments on declaration onto separate lines
at the top of the file then ok, but why all the way down here?

Thanks,

-- 
Julian Calaby

Email: julian.calaby@...il.com
Profile: http://www.google.com/profiles/julian.calaby/