From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Puranjay Mohan <puranjay12@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>,
Shubham Bansal <illusionist.neo@gmail.com>,
Mykola Lysenko <mykolal@fb.com>, Shuah Khan <shuah@kernel.org>,
bpf@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf-next v2 4/8] arm32, bpf: add support for unconditional bswap instruction
Date: Thu, 7 Sep 2023 10:15:06 +0100 [thread overview]
Message-ID: <ZPmUmqzvq1sV7r/f@shell.armlinux.org.uk> (raw)
In-Reply-To: <mb61pzg1y1hb5.fsf@amazon.com>
On Thu, Sep 07, 2023 at 09:08:46AM +0000, Puranjay Mohan wrote:
> On Thu, Sep 07 2023, Russell King (Oracle) wrote:
>
> > On Wed, Sep 06, 2023 at 06:33:16PM +0000, Puranjay Mohan wrote:
> >> @@ -1633,8 +1633,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx)
> >> /* dst = htobe(dst) */
> >> case BPF_ALU | BPF_END | BPF_FROM_LE:
> >> case BPF_ALU | BPF_END | BPF_FROM_BE:
> >> + /* dst = bswap(dst) */
> >> + case BPF_ALU64 | BPF_END | BPF_TO_LE:
> >> rd = arm_bpf_get_reg64(dst, tmp, ctx);
> >> - if (BPF_SRC(code) == BPF_FROM_LE)
> >> + if (BPF_SRC(code) == BPF_FROM_LE && BPF_CLASS(code) != BPF_ALU64)
> >
> > With the addition of the BPF_ALU64 case, I'm wondering why this if() is
> > affected. If you were adding:
> >
> > case BPF_ALU64 | BPF_END | BPF_FROM_LE:
> >
> > then maybe there would be a reason, but the BPF_ALU64 | BPF_END |
> > BPF_TO_LE case will never match even the original if() statement.
>
> The reason is that these mean the same thing.
> from: include/uapi/linux/bpf.h
>
> #define BPF_TO_LE 0x00 /* convert to little-endian */
> #define BPF_TO_BE 0x08 /* convert to big-endian */
> #define BPF_FROM_LE BPF_TO_LE
> #define BPF_FROM_BE BPF_TO_BE
>
> So, to not cause confusion and follow the earlier cases I can add:
>
> case BPF_ALU64 | BPF_END | BPF_FROM_LE:
>
> in the next version.
It might be worth adding a comment after each stating one of:
/* also BPF_TO_LE */
/* also BPF_TO_BE */
as appropriate to make this more readable.
Thanks.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
next prev parent reply other threads:[~2023-09-07 16:24 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-06 18:33 [PATCH bpf-next v2 0/8] arm32, bpf: add support for cpuv4 insns Puranjay Mohan
2023-09-06 18:33 ` [PATCH bpf-next v2 1/8] arm32, bpf: add support for 32-bit offset jmp instruction Puranjay Mohan
2023-09-07 8:39 ` Russell King (Oracle)
2023-09-06 18:33 ` [PATCH bpf-next v2 2/8] arm32, bpf: add support for sign-extension load instruction Puranjay Mohan
2023-09-07 8:44 ` Russell King (Oracle)
2023-09-06 18:33 ` [PATCH bpf-next v2 3/8] arm32, bpf: add support for sign-extension mov instruction Puranjay Mohan
2023-09-07 8:45 ` Russell King (Oracle)
2023-09-06 18:33 ` [PATCH bpf-next v2 4/8] arm32, bpf: add support for unconditional bswap instruction Puranjay Mohan
2023-09-07 8:48 ` Russell King (Oracle)
2023-09-07 9:08 ` Puranjay Mohan
2023-09-07 9:15 ` Russell King (Oracle) [this message]
2023-09-06 18:33 ` [PATCH bpf-next v2 5/8] arm32, bpf: add support for 32-bit signed division Puranjay Mohan
2023-09-07 8:49 ` Russell King (Oracle)
2023-09-06 18:33 ` [PATCH bpf-next v2 6/8] arm32, bpf: add support for 64 bit division instruction Puranjay Mohan
2023-09-07 8:50 ` Russell King (Oracle)
2023-09-06 18:33 ` [PATCH bpf-next v2 7/8] selftest, bpf: enable cpu v4 tests for arm32 Puranjay Mohan
2023-09-06 18:33 ` [PATCH bpf-next v2 8/8] bpf/tests: add tests for cpuv4 instructions Puranjay Mohan
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