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Message-ID: <a76d41c28918dbdf046e5bc73b9ed67a093e02a1.camel@russell.cc>
Date: Mon, 16 May 2022 13:03:35 +1000
From: Russell Currey <ruscur@...sell.cc>
To: Hari Bathini <hbathini@...ux.ibm.com>, bpf@...r.kernel.org,
linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Cc: Song Liu <songliubraving@...com>,
Daniel Borkmann <daniel@...earbox.net>,
John Fastabend <john.fastabend@...il.com>,
Alexei Starovoitov <ast@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>, netdev@...r.kernel.org,
Paul Mackerras <paulus@...ba.org>,
"Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
Yonghong Song <yhs@...com>, KP Singh <kpsingh@...nel.org>,
Jordan Niethe <jniethe5@...il.com>,
Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH 3/5] bpf ppc64: Add instructions for atomic_[cmp]xchg
On Thu, 2022-05-12 at 13:15 +0530, Hari Bathini wrote:
> This adds two atomic opcodes BPF_XCHG and BPF_CMPXCHG on ppc64, both
> of which include the BPF_FETCH flag. The kernel's atomic_cmpxchg
> operation fundamentally has 3 operands, but we only have two register
> fields. Therefore the operand we compare against (the kernel's API
> calls it 'old') is hard-coded to be BPF_REG_R0. Also, kernel's
> atomic_cmpxchg returns the previous value at dst_reg + off. JIT the
> same for BPF too with return value put in BPF_REG_0.
>
> BPF_REG_R0 = atomic_cmpxchg(dst_reg + off, BPF_REG_R0, src_reg);
>
> Signed-off-by: Hari Bathini <hbathini@...ux.ibm.com>
> ---
> arch/powerpc/net/bpf_jit_comp64.c | 28 ++++++++++++++++++++++++----
> 1 file changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c
> b/arch/powerpc/net/bpf_jit_comp64.c
> index 504fa459f9f3..df9e20b22ccb 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -783,6 +783,9 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32
> *image, struct codegen_context *
> */
> case BPF_STX | BPF_ATOMIC | BPF_W:
> case BPF_STX | BPF_ATOMIC | BPF_DW:
> + u32 save_reg = tmp2_reg;
> + u32 ret_reg = src_reg;
Hi Hari,
Some compilers[0][1] don't like these late declarations after case
labels:
arch/powerpc/net/bpf_jit_comp64.c: In function ‘bpf_jit_build_body’:
arch/powerpc/net/bpf_jit_comp64.c:781:4: error: a label can only be
part of a statement and a declaration is not a statement
u32 save_reg = tmp2_reg;
^~~
arch/powerpc/net/bpf_jit_comp64.c:782:4: error: expected expression
before ‘u32’
u32 ret_reg = src_reg;
^~~
arch/powerpc/net/bpf_jit_comp64.c:819:5: error: ‘ret_reg’ undeclared
(first use in this function); did you mean ‘dst_reg’?
ret_reg = bpf_to_ppc(BPF_REG_0);
Adding a semicolon fixes the first issue, i.e.
case BPF_STX | BPF_ATOMIC | BPF_DW: ;
but then it just complains about mixed declarations and code instead.
So you should declare save_reg and ret_reg at the beginning of the for
loop like the rest of the variables.
- Russell
[0]: gcc 5.5.0
https://github.com/ruscur/linux-ci/runs/6418546193?check_suite_focus=true#step:4:122
[1]: clang 12.0
https://github.com/ruscur/linux-ci/runs/6418545338?check_suite_focus=true#step:4:117
> +
> /* Get offset into TMP_REG_1 */
> EMIT(PPC_RAW_LI(tmp1_reg, off));
> tmp_idx = ctx->idx * 4;
> @@ -813,6 +816,24 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32
> *image, struct codegen_context *
> case BPF_XOR | BPF_FETCH:
> EMIT(PPC_RAW_XOR(tmp2_reg, tmp2_reg,
> src_reg));
> break;
> + case BPF_CMPXCHG:
> + /*
> + * Return old value in BPF_REG_0 for
> BPF_CMPXCHG &
> + * in src_reg for other cases.
> + */
> + ret_reg = bpf_to_ppc(BPF_REG_0);
> +
> + /* Compare with old value in BPF_R0
> */
> + if (size == BPF_DW)
> + EMIT(PPC_RAW_CMPD(bpf_to_ppc(
> BPF_REG_0), tmp2_reg));
> + else
> + EMIT(PPC_RAW_CMPW(bpf_to_ppc(
> BPF_REG_0), tmp2_reg));
> + /* Don't set if different from old
> value */
> + PPC_BCC_SHORT(COND_NE, (ctx->idx + 3)
> * 4);
> + fallthrough;
> + case BPF_XCHG:
> + save_reg = src_reg;
> + break;
> default:
> pr_err_ratelimited(
> "eBPF filter atomic op code
> %02x (@%d) unsupported\n",
> @@ -822,15 +843,14 @@ int bpf_jit_build_body(struct bpf_prog *fp, u32
> *image, struct codegen_context *
>
> /* store new value */
> if (size == BPF_DW)
> - EMIT(PPC_RAW_STDCX(tmp2_reg,
> tmp1_reg, dst_reg));
> + EMIT(PPC_RAW_STDCX(save_reg,
> tmp1_reg, dst_reg));
> else
> - EMIT(PPC_RAW_STWCX(tmp2_reg,
> tmp1_reg, dst_reg));
> + EMIT(PPC_RAW_STWCX(save_reg,
> tmp1_reg, dst_reg));
> /* we're done if this succeeded */
> PPC_BCC_SHORT(COND_NE, tmp_idx);
>
> - /* For the BPF_FETCH variant, get old value
> into src_reg */
> if (imm & BPF_FETCH)
> - EMIT(PPC_RAW_MR(src_reg, _R0));
> + EMIT(PPC_RAW_MR(ret_reg, _R0));
> break;
>
> /*
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