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Tue, 28 Nov 2023 12:54:53 -0500 (EST) From: Daniel Xu To: ndesaulniers@google.com, andrii@kernel.org, nathan@kernel.org, daniel@iogearbox.net, ast@kernel.org, steffen.klassert@secunet.com, antony.antony@secunet.com, alexei.starovoitov@gmail.com, yonghong.song@linux.dev, eddyz87@gmail.com Cc: martin.lau@linux.dev, song@kernel.org, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, trix@redhat.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, devel@linux-ipsec.org, netdev@vger.kernel.org Subject: [PATCH ipsec-next v2 3/6] libbpf: Add BPF_CORE_WRITE_BITFIELD() macro Date: Tue, 28 Nov 2023 10:54:23 -0700 Message-ID: X-Mailer: git-send-email 2.42.1 In-Reply-To: References: MIME-Version: 1.0 X-Spam-Status: No, score=-0.9 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lipwig.vger.email Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (lipwig.vger.email [0.0.0.0]); Tue, 28 Nov 2023 09:56:24 -0800 (PST) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1783831399014738219 X-GMAIL-MSGID: 1783831399014738219 Similar to reading from CO-RE bitfields, we need a CO-RE aware bitfield writing wrapper to make the verifier happy. Two alternatives to this approach are: 1. Use the upcoming `preserve_static_offset` [0] attribute to disable CO-RE on specific structs. 2. Use broader byte-sized writes to write to bitfields. (1) is a bit a bit hard to use. It requires specific and not-very-obvious annotations to bpftool generated vmlinux.h. It's also not generally available in released LLVM versions yet. (2) makes the code quite hard to read and write. And especially if BPF_CORE_READ_BITFIELD() is already being used, it makes more sense to to have an inverse helper for writing. [0]: https://reviews.llvm.org/D133361 From: Eduard Zingerman Signed-off-by: Daniel Xu --- tools/lib/bpf/bpf_core_read.h | 36 +++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h index 1ac57bb7ac55..7a764f65d299 100644 --- a/tools/lib/bpf/bpf_core_read.h +++ b/tools/lib/bpf/bpf_core_read.h @@ -111,6 +111,42 @@ enum bpf_enum_value_kind { val; \ }) +/* + * Write to a bitfield, identified by s->field. + * This is the inverse of BPF_CORE_WRITE_BITFIELD(). + */ +#define BPF_CORE_WRITE_BITFIELD(s, field, new_val) ({ \ + void *p = (void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \ + unsigned int byte_size = __CORE_RELO(s, field, BYTE_SIZE); \ + unsigned int lshift = __CORE_RELO(s, field, LSHIFT_U64); \ + unsigned int rshift = __CORE_RELO(s, field, RSHIFT_U64); \ + unsigned int bit_size = (rshift - lshift); \ + unsigned long long nval, val, hi, lo; \ + \ + asm volatile("" : "+r"(p)); \ + \ + switch (byte_size) { \ + case 1: val = *(unsigned char *)p; break; \ + case 2: val = *(unsigned short *)p; break; \ + case 4: val = *(unsigned int *)p; break; \ + case 8: val = *(unsigned long long *)p; break; \ + } \ + hi = val >> (bit_size + rshift); \ + hi <<= bit_size + rshift; \ + lo = val << (bit_size + lshift); \ + lo >>= bit_size + lshift; \ + nval = new_val; \ + nval <<= lshift; \ + nval >>= rshift; \ + val = hi | nval | lo; \ + switch (byte_size) { \ + case 1: *(unsigned char *)p = val; break; \ + case 2: *(unsigned short *)p = val; break; \ + case 4: *(unsigned int *)p = val; break; \ + case 8: *(unsigned long long *)p = val; break; \ + } \ +}) + #define ___bpf_field_ref1(field) (field) #define ___bpf_field_ref2(type, field) (((typeof(type) *)0)->field) #define ___bpf_field_ref(args...) \