linux-kernel - Re: [PATCH v1 2/2] LoongArch: BPF: Fix unconditional bswap instructions

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Date:   Sat, 9 Dec 2023 20:01:44 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Hengqi Chen <hengqi.chen@...il.com>
Cc:     Tiezhu Yang <yangtiezhu@...ngson.cn>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] LoongArch: BPF: Fix unconditional bswap instructions

Applied, thanks.

Huacai

On Sat, Dec 9, 2023 at 2:06 PM Hengqi Chen <hengqi.chen@...il.com> wrote:
>
> On Thu, Dec 7, 2023 at 11:30 AM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
> >
> > We can see that "bswap32: Takes an unsigned 32-bit number in either
> > big- or little-endian format and returns the equivalent number with
> > the same bit width but opposite endianness" in BPF Instruction Set
> > Specification, so it should clear the upper 32 bits in the case 32
> > for BPF_ALU and BPF_ALU64.
> >
> > [root@...ux fedora]# echo 1 > /proc/sys/net/core/bpf_jit_enable
> > [root@...ux fedora]# modprobe test_bpf
> >
> > Before:
> > test_bpf: #313 BSWAP 32: 0x0123456789abcdef -> 0xefcdab89 jited:1 ret 1460850314 != -271733879 (0x5712ce8a != 0xefcdab89)FAIL (1 times)
> > test_bpf: #317 BSWAP 32: 0xfedcba9876543210 -> 0x10325476 jited:1 ret -1460850316 != 271733878 (0xa8ed3174 != 0x10325476)FAIL (1 times)
> >
> > After:
> > test_bpf: #313 BSWAP 32: 0x0123456789abcdef -> 0xefcdab89 jited:1 4 PASS
> > test_bpf: #317 BSWAP 32: 0xfedcba9876543210 -> 0x10325476 jited:1 4 PASS
> >
>
> Nice catch. I wasn't aware of test_bpf before. For the patch:
>
> Acked-by: Hengqi Chen <hengqi.chen@...il.com>
>
> > Fixes: 4ebf9216e7df ("LoongArch: BPF: Support unconditional bswap instructions")
> > Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> > ---
> >  arch/loongarch/net/bpf_jit.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
> > index 8c907c2c42f7..da48398e8794 100644
> > --- a/arch/loongarch/net/bpf_jit.c
> > +++ b/arch/loongarch/net/bpf_jit.c
> > @@ -774,8 +774,8 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext
> >                         break;
> >                 case 32:
> >                         emit_insn(ctx, revb2w, dst, dst);
> > -                       /* zero-extend 32 bits into 64 bits */
> > -                       emit_zext_32(ctx, dst, is32);
> > +                       /* clear the upper 32 bits */
> > +                       emit_zext_32(ctx, dst, true);
> >                         break;
> >                 case 64:
> >                         emit_insn(ctx, revbd, dst, dst);
> > --
> > 2.42.0
> >