netdev - Re: [PATCH v2] arm: eBPF JIT compiler

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Date:   Mon, 12 Jun 2017 12:06:11 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Kees Cook <keescook@...omium.org>,
        Shubham Bansal <illusionist.neo@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>, Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH v2] arm: eBPF JIT compiler

On Mon, Jun 12, 2017 at 12:21:03PM +0200, Daniel Borkmann wrote:
> On 05/30/2017 09:19 PM, Kees Cook wrote:
> >On Thu, May 25, 2017 at 4:13 PM, Shubham Bansal
> ><illusionist.neo@...il.com> wrote:
> >>+static int validate_code(struct jit_ctx *ctx)
> >>+{
> >>+       int i;
> >>+
> >>+       for (i = 0; i < ctx->idx; i++) {
> >>+               u32 a32_insn = le32_to_cpu(ctx->target[i]);
> 
> Given __opcode_to_mem_arm(ARM_INST_UDF) is used to fill the image,
> perhaps use the __mem_to_opcode_arm() helper for the check?
> 
> >>+               if (a32_insn == ARM_INST_UDF)

The following is probably better:

		if (ctx->target[i] == __opcode_to_mem_arm(ARM_INST_UDF))

since then you can take advantage of the compiler optimising the
constant rather than having to do a byte swap on an unknown 32-bit
value.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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