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Mon, 14 Sep 2026 19:14:16 -0700 (PDT) From: Nicholas Dudar To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, udknight@gmail.com, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org Cc: martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, emil@etsalapatis.com, ihor.solodrai@linux.dev, hpa@zytor.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, visitorckw@gmail.com Subject: [PATCH bpf-next 4/5] bpf, x86: Add BPF_JMP32 | BPF_JA support to the i386 JIT Date: Mon, 14 Sep 2026 22:13:37 -0400 Message-ID: <20260915021338.1520964-5-main.kalliope@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260915021338.1520964-1-main.kalliope@gmail.com> References: <20260915021338.1520964-1-main.kalliope@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The i386 JIT rejects BPF_JMP32 | BPF_JA, which encodes its signed jump displacement in imm rather than the 16-bit off field. Select the displacement by instruction class and reuse the existing unconditional jump lowering, including its self-jump and no-op handling. The shared unconditional-jump path handles instruction zero separately: its start is the prologue boundary, which has no preceding entry in the instruction-end address map. Assisted-by: Codex:gpt-6 Signed-off-by: Nicholas Dudar --- arch/x86/net/bpf_jit_comp32.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c index bbe48b15850f..2d8a3a961e91 100644 --- a/arch/x86/net/bpf_jit_comp32.c +++ b/arch/x86/net/bpf_jit_comp32.c @@ -1821,6 +1821,7 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, const u8 *src = bpf2ia32[insn->src_reg]; const u8 *r0 = bpf2ia32[BPF_REG_0]; s64 jmp_offset; + s32 ja_off; u8 jmp_cond; int ilen; u8 *func; @@ -2522,7 +2523,9 @@ emit_cond_jmp_signed: /* Check the condition for low 32-bit comparison */ break; } case BPF_JMP | BPF_JA: - if (insn->off == -1) + case BPF_JMP32 | BPF_JA: + ja_off = BPF_CLASS(code) == BPF_JMP32 ? imm32 : insn->off; + if (ja_off == -1) /* -1 jmp instructions will always jump * backwards two bytes. Explicitly handling * this case avoids wasting too many passes @@ -2530,8 +2533,10 @@ emit_cond_jmp_signed: /* Check the condition for low 32-bit comparison */ * dead code. */ jmp_offset = -2; + else if (i + ja_off == -1) + jmp_offset = PROLOGUE_SIZE - addrs[i]; else - jmp_offset = addrs[i + insn->off] - addrs[i]; + jmp_offset = addrs[i + ja_off] - addrs[i]; if (!jmp_offset) /* Optimize out nop jumps */