linux-kernel - Re: [PATCH bpf-next 1/8] arm32, bpf: add support for 32-bit offset jmp instruction

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Message-ID: <ZPeZhhAciDRgGL+s@shell.armlinux.org.uk>
Date:   Tue, 5 Sep 2023 22:11:34 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Puranjay Mohan <puranjay12@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        Yonghong Song <yonghong.song@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Shubham Bansal <illusionist.neo@...il.com>,
        Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
        bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/8] arm32, bpf: add support for 32-bit offset
 jmp instruction

On Tue, Sep 05, 2023 at 09:06:14PM +0000, Puranjay Mohan wrote:
> The cpuv4 adds unconditional jump with 32-bit offset where the immediate
> field of the instruction is to be used to calculate the jump offset.
> 
> BPF_JA | BPF_K | BPF_JMP32 => gotol +imm => PC += imm.
> 
> Signed-off-by: Puranjay Mohan <puranjay12@...il.com>
> ---
>  arch/arm/net/bpf_jit_32.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
> index 6a1c9fca5260..b26579da770e 100644
> --- a/arch/arm/net/bpf_jit_32.c
> +++ b/arch/arm/net/bpf_jit_32.c
> @@ -1761,10 +1761,15 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
>  		break;
>  	/* JMP OFF */
>  	case BPF_JMP | BPF_JA:
> +	case BPF_JMP32 | BPF_JA:
>  	{
> -		if (off == 0)
> +		if (BPF_CLASS(code) == BPF_JMP32 && imm != 0)
> +			jmp_offset = bpf2a32_offset(i + imm, i, ctx);
> +		else if (BPF_CLASS(code) == BPF_JMP &&  off != 0)

Please tidy up the coding style - one space between "&&" and "off"

Thanks.

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