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Sat, 31 Oct 2026 10:19:16 -0700 (PDT) Received: from localhost ([153.61.198.246]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cdb09706f01sm1745003a12.20.2026.10.31.10.19.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 31 Oct 2026 10:19:15 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Sat, 31 Oct 2026 17:19:15 +0000 Message-Id: Cc: , , , , , , , , , Subject: Re: [PATCH bpf-next v3 02/13] libbpf: Dump kflagged BTF tags as is From: "Alexei Starovoitov" To: "Ihor Solodrai" , , , , , , In-Reply-To: References: <20261030233355.1836749-3-ihor.solodrai@linux.dev> 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 Fri, Oct 30, 2026 at 05:36 PM Ihor Solodrai wrote: > The incompatibility affects: > - old kernel BTF + bpftool before patch "bpftool: Normalize legacy > arena type tags before C dumps" > - new kernel + old bpftool, in which case the users will have to > update their bpftool I don't think we can accept the second one. Every bpftool since v6.15 wraps the new string and prints void __attribute__((__attribute__((address_space(1))))) * for the arena kfuncs. After a kernel upgrade no prog that includes it compiles, unless it defines BPF_NO_KFUNC_PROTOTYPES. It's not only arena progs. The list misses module BTF. Patch 4 skips split BTF, so on old kernels the new bpftool prints "void address_space(1) *" there. People do such dumps. See commit d8d5c0151148 ("bpftool: Support merging multiple module BTFs in btf dump"). can we leave type tags alone and print only decl tags as is ? bpftool adds decl tags only. It adds them to a split BTF in memory and dumps them with its own libbpf. Nobody else sees them. Kernel BTF has no kflagged decl tags on records, I think. Then no need for the resolve_btfids change, patches 4 and 6, etc. pw-bot: cr