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([2620:10d:c090:500::4:432]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-32ed26a592dsm781758a91.10.2025.09.16.18.05.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Sep 2025 18:05:31 -0700 (PDT) Message-ID: Subject: Re: [PATCH bpf-next v3 1/3] bpf, x86: Add support for signed arena loads From: Eduard Zingerman To: Puranjay Mohan , bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , kkd@meta.com, kernel-team@meta.com, Kumar Kartikeya Dwivedi Date: Tue, 16 Sep 2025 18:05:29 -0700 In-Reply-To: <20250915162848.54282-2-puranjay@kernel.org> References: <20250915162848.54282-1-puranjay@kernel.org> <20250915162848.54282-2-puranjay@kernel.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-1.fc42) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2025-09-15 at 16:28 +0000, Puranjay Mohan wrote: [...] > diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.= c > index 008273a53e04..f2b85a10add2 100644 > --- a/arch/arm64/net/bpf_jit_comp.c > +++ b/arch/arm64/net/bpf_jit_comp.c > @@ -3064,6 +3064,11 @@ bool bpf_jit_supports_insn(struct bpf_insn *insn, = bool in_arena) > if (!bpf_atomic_is_load_store(insn) && > !cpus_have_cap(ARM64_HAS_LSE_ATOMICS)) > return false; > + break; > + case BPF_LDX | BPF_MEMSX | BPF_B: > + case BPF_LDX | BPF_MEMSX | BPF_H: > + case BPF_LDX | BPF_MEMSX | BPF_W: > + return false; > } > return true; > } Is the same hunk necessary in riscv/net/bpf_jit_comp64.c? [...] > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c > index 8d34a9400a5e..a6550da34268 100644 > --- a/arch/x86/net/bpf_jit_comp.c > +++ b/arch/x86/net/bpf_jit_comp.c > @@ -1152,11 +1152,38 @@ static void emit_ldx_index(u8 **pprog, u32 size, = u32 dst_reg, u32 src_reg, u32 i > *pprog =3D prog; > } > =20 > +static void emit_ldsx_index(u8 **pprog, u32 size, u32 dst_reg, u32 src_r= eg, u32 index_reg, int off) > +{ > + u8 *prog =3D *pprog; > + > + switch (size) { > + case BPF_B: > + /* movsx rax, byte ptr [rax + r12 + off] */ > + EMIT3(add_3mod(0x48, src_reg, dst_reg, index_reg), 0x0F, 0xBE); > + break; > + case BPF_H: > + /* movsx rax, word ptr [rax + r12 + off] */ > + EMIT3(add_3mod(0x48, src_reg, dst_reg, index_reg), 0x0F, 0xBF); > + break; > + case BPF_W: > + /* movsx rax, dword ptr [rax + r12 + off] */ > + EMIT2(add_3mod(0x48, src_reg, dst_reg, index_reg), 0x63); > + break; > + } > + emit_insn_suffix_SIB(&prog, src_reg, dst_reg, index_reg, off); > + *pprog =3D prog; > +} > + Encoding looks correct. [...] > @@ -2109,13 +2136,19 @@ st: if (is_imm8(insn->off)) > case BPF_LDX | BPF_PROBE_MEM32 | BPF_H: > case BPF_LDX | BPF_PROBE_MEM32 | BPF_W: > case BPF_LDX | BPF_PROBE_MEM32 | BPF_DW: > + case BPF_LDX | BPF_PROBE_MEM32SX | BPF_B: > + case BPF_LDX | BPF_PROBE_MEM32SX | BPF_H: > + case BPF_LDX | BPF_PROBE_MEM32SX | BPF_W: > case BPF_STX | BPF_PROBE_MEM32 | BPF_B: > case BPF_STX | BPF_PROBE_MEM32 | BPF_H: > case BPF_STX | BPF_PROBE_MEM32 | BPF_W: > case BPF_STX | BPF_PROBE_MEM32 | BPF_DW: > start_of_ldx =3D prog; > if (BPF_CLASS(insn->code) =3D=3D BPF_LDX) > - emit_ldx_r12(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->of= f); > + if (BPF_MODE(insn->code) =3D=3D BPF_PROBE_MEM32SX) > + emit_ldsx_r12(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->= off); > + else > + emit_ldx_r12(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->o= ff); > else > emit_stx_r12(&prog, BPF_SIZE(insn->code), dst_reg, src_reg, insn->of= f); Heh, apparently this is correct C code. Dangling else is associated with the closest 'if' statement. Didn't know that. [...]