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Tue, 03 Nov 2026 16:44:26 -0800 (PST) Received: from localhost ([153.61.198.240]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b094d572e7sm567255a91.1.2026.11.03.16.44.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Nov 2026 16:44:25 -0800 (PST) Content-Type: text/plain; charset=UTF-8 Date: Wed, 04 Nov 2026 00:44:25 +0000 Message-Id: Subject: Re: [PATCH bpf-next] selftests/bpf: Account for zero extensions in patch list expectations From: "Alexei Starovoitov" To: "Hungyu Lin" , Cc: , , , , , , , , In-Reply-To: <20261103215309.19950-1-dennylin0707@gmail.com> References: <20261103215309.19950-1-dennylin0707@gmail.com> Content-Transfer-Encoding: 8bit X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Tue, Nov 03, 2026 at 01:53 PM Hungyu Lin wrote: > patch_list_insert_in_front() checks the translated instructions around > the call of an inlined bpf_loop() and its callback. On s390, the verifier > adds zero extensions after the two 32-bit register writes in the loop. Thanks a bunch. Applied. But could you follow up to remove the two 32-bit writes from inline_bpf_loop(). 'w7 = 0' and 'r7 = 0' do the same thing. 'w0 = -E2BIG' is an old bug. bpf_loop() returns long. The helper returns 0xfffffffffffffff9. The inlined code returns 0xfffffff9. So 'long ret = bpf_loop(...); if (ret < 0)' misses the error. The "over max limit" check in prog_tests/bpf_loop.c doesn't see it. The prog keeps the result in an int. No other insn of this prog writes 32 bits. With 64-bit writes the xlated code is the same on all five archs. Then no need for the #if and the second copy of the expectations. Something like this (compile tested only): diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c index 6b719a2..321624a 100644 --- a/kernel/bpf/fixups.c +++ b/kernel/bpf/fixups.c @@ -2783,7 +2783,7 @@ static int inline_bpf_loop(struct bpf_verifier_env *env, int position, * expected number of iterations is too big. */ insn_buf[cnt++] = BPF_JMP_IMM(BPF_JLE, BPF_REG_1, BPF_MAX_LOOPS, 2); - insn_buf[cnt++] = BPF_MOV32_IMM(BPF_REG_0, -E2BIG); + insn_buf[cnt++] = BPF_MOV64_IMM(BPF_REG_0, -E2BIG); insn_buf[cnt++] = BPF_JMP_IMM(BPF_JA, 0, 0, 16); /* spill R6, R7, R8 to use these as loop vars */ insn_buf[cnt++] = BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_6, r6_offset); @@ -2791,7 +2791,7 @@ static int inline_bpf_loop(struct bpf_verifier_env *env, int position, insn_buf[cnt++] = BPF_STX_MEM(BPF_DW, BPF_REG_10, BPF_REG_8, r8_offset); /* initialize loop vars */ insn_buf[cnt++] = BPF_MOV64_REG(reg_loop_max, BPF_REG_1); - insn_buf[cnt++] = BPF_MOV32_IMM(reg_loop_cnt, 0); + insn_buf[cnt++] = BPF_MOV64_IMM(reg_loop_cnt, 0); insn_buf[cnt++] = BPF_MOV64_REG(reg_loop_ctx, BPF_REG_3); /* loop header, * if reg_loop_cnt >= reg_loop_max skip the loop body