From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.28 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793403291; b=RjIMkzlzn7gorK0drpK7w+iyH/5E6297dgvQus9d4V0Q3zx7XDJrqEVBDuYj98cmeZIX zmy4jilRaJO3RQPRpUeIz/R2+Lo7fX/AzOkG4VXE8pqGMR0VIDAU4uM7fTQFh55kv4eUJ Vli+bB5T1hAe3k61pRG9fY03LSOMrixEwu1+DyaD47E7lLVFBQ2l66kz/duOqyP3y5D8V QY9Bk7pz2cGsad6zHXWP4koP5KGq9SojeQIm/7uSAz4ma7DszlTawnASIw4vdy7ubf4U+ H2AySeOKkoBzwWdCjwPI82D2l/pDLfKTxffEVbqA0lCh/UCALrNQhhj5UDC2FdIR25Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793403291; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version: Content-Transfer-Encoding; bh=UP4Mh8dUAUMHFxLvakJazUBpQ0KyNmEbtA2CeEn1vkM=; b=3ipKzRwaoKuKmuvAxhSwD7ALRgWb/s5xCWQtIXlN1FRvu0OJxzbq6YaHXr+BekvkStX7 BDsQM/pURfdEx8cSH6hk/7zImDnR/riDVJlISYxN/AWjQ1GTuxNZ/fmsze8VtIHxci7YH obFitwEY2RmYx6X9Cn8BNGRDTdfb3fXYSJSOhFr5dwco3gKGZnoV/kyZ+qu8eZwRRjYmu FqQyMkS6160e53ydl2C5jfE/u06+RLsqzLgA81X4C9fYyx0pl0V7dbz8br8uN9w0tPAfJ 6FamImqKxAn81gkCU8Q8whsyRWQWds7doq99/0ze2HgCjK0XAJ1RDtW7koad/pF3/bQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=IRCZYrFc; arc=none smtp.remote-ip=91.218.175.28 Received: from mta0.migadu.com (out-28.mta0.migadu.com [91.218.175.28]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7072F606A325 for ; Fri, 30 Oct 2026 23:34:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 7072F606A325 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=IRCZYrFc X-Envelope-To: bpf@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=28z+0mBn5pCcbPz/HtFwvcTQyMELRP0X9g3gV/iyBak=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793403288; v=1; x=1794008088; b=IRCZYrFchhy6iVtfZe/58l4I+ImEcvmd4GBc2wJXWfdesodmuLZalgN5UPylmfX+MqLsahQi 4+GWlZlE3r5WhijEV2v5qySHJPv1AY2D5zjScrh9RjW8L0UciLGY6/VNL1DckV3ZNCr3+jyckzX zrWpXTiyvknt3Uz5zEJ4thRU= X-Envelope-To: bpf@vger.kernel.org Received: by mta12.migadu.com with ESMTPS id fa8c08e570eeab58; Fri, 30 Oct 2026 23:34:48 +0000 X-Mizu-Trace-ID: fa8c08e570eeab58 X-Migadu-Flow: FLOW_OUT From: Ihor Solodrai To: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Eduard Zingerman , Kumar Kartikeya Dwivedi , Quentin Monnet Cc: bpf@vger.kernel.org, Alan Maguire , Cupertino Miranda , David Faust , Ian Rogers , "Jose E . Marchesi" , Vineet Gupta , Yonghong Song Subject: [PATCH bpf-next v3 10/13] bpftool: Emit __bpf_static_offset on verifier-rewritten context types Date: Fri, 30 Oct 2026 16:33:52 -0700 Message-ID: <20261030233355.1836749-11-ihor.solodrai@linux.dev> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261030233355.1836749-1-ihor.solodrai@linux.dev> References: <20261030233355.1836749-1-ihor.solodrai@linux.dev> 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 Content-Transfer-Encoding: 8bit The verifier translates accesses to some UAPI context and socket types into accesses to kernel structures. These accesses require an unmodified base and an immediate field offset. Leaving preserve_access_index (PAI) off does not stop the compiler from merging loads at different field offsets into one load through an adjusted pointer. The verifier rejects the resulting program. preserve_static_offset (PSO), available since Clang 18, preserves static field offsets in load and store instruction immediates. Apply it to the 13 types that need static offsets in vmlinux.h through __bpf_static_offset. Eduard introduced PSO in Clang and proposed annotating BPF context types in 2023 [1]. His v3 RFC [2] left pt_regs annotations in architecture headers unresolved. However, since commit de6c7d99f898 ("bpf: Relax fixed offset check for PTR_TO_CTX"), program types without convert_ctx_access() accept fixed offsets from modified context pointers. pt_regs can now keep PAI, while PSO on bpf_perf_event_data covers its regs member. PSO creates no CO-RE relocations, so BPF_NO_PRESERVE_ACCESS_INDEX does not disable it. Clang 18 through 23 crash on __builtin_preserve_field_info over a PSO record, including bpf_core_field_*() and the CO-RE bitfield helpers. -D__bpf_static_offset= can disable PSO for affected programs. The crash has already been forward fixed in LLVM [3]. [1]: https://lore.kernel.org/bpf/20231208000531.19179-1-eddyz87@gmail.com/ [2]: https://lore.kernel.org/bpf/20231220133411.22978-1-eddyz87@gmail.com/ [3]: https://github.com/llvm/llvm-project/pull/234280 Signed-off-by: Ihor Solodrai --- tools/bpf/bpftool/btf.c | 16 ++++++++++++++-- .../bpf/bpftool_btf_dump_sorted.expected | 8 ++++++++ .../bpf/bpftool_btf_dump_unsorted.expected | 8 ++++++++ 3 files changed, 30 insertions(+), 2 deletions(-) diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c index 86ab844898db..03da4f6821f1 100644 --- a/tools/bpf/bpftool/btf.c +++ b/tools/bpf/bpftool/btf.c @@ -1204,12 +1204,17 @@ static int btf_c_annotate_records(struct btf *btf) for (i = 1; i < cnt; i++) { const struct btf_type *t = btf__type_by_id(btf, i); + const char *attr; if (!btf_is_composite(t)) continue; - if (non_relocatable[i]) + if (!non_relocatable[i]) + attr = "__bpf_relocatable"; + else if (btf_c_needs_static_offset(btf, t)) + attr = "__bpf_static_offset"; + else continue; - err = btf__add_decl_attr(btf, "__bpf_relocatable", i, -1); + err = btf__add_decl_attr(btf, attr, i, -1); if (err < 0) goto out; } @@ -1262,6 +1267,13 @@ static int dump_btf_c(struct btf *btf, printf("#define __bpf_relocatable\n"); printf("#endif\n"); printf("#endif\n\n"); + printf("#ifndef __bpf_static_offset\n"); + printf("#if __has_attribute(preserve_static_offset)\n"); + printf("#define __bpf_static_offset __attribute__((preserve_static_offset))\n"); + printf("#else\n"); + printf("#define __bpf_static_offset\n"); + printf("#endif\n"); + printf("#endif\n\n"); printf("#ifndef __ksym\n"); printf("#define __ksym __attribute__((section(\".ksyms\")))\n"); printf("#endif\n\n"); diff --git a/tools/testing/selftests/bpf/bpftool_btf_dump_sorted.expected b/tools/testing/selftests/bpf/bpftool_btf_dump_sorted.expected index f2389e3dceed..b56b676b96a5 100644 --- a/tools/testing/selftests/bpf/bpftool_btf_dump_sorted.expected +++ b/tools/testing/selftests/bpf/bpftool_btf_dump_sorted.expected @@ -9,6 +9,14 @@ #endif #endif +#ifndef __bpf_static_offset +#if __has_attribute(preserve_static_offset) +#define __bpf_static_offset __attribute__((preserve_static_offset)) +#else +#define __bpf_static_offset +#endif +#endif + #ifndef __ksym #define __ksym __attribute__((section(".ksyms"))) #endif diff --git a/tools/testing/selftests/bpf/bpftool_btf_dump_unsorted.expected b/tools/testing/selftests/bpf/bpftool_btf_dump_unsorted.expected index 549045677a45..543db89078af 100644 --- a/tools/testing/selftests/bpf/bpftool_btf_dump_unsorted.expected +++ b/tools/testing/selftests/bpf/bpftool_btf_dump_unsorted.expected @@ -9,6 +9,14 @@ #endif #endif +#ifndef __bpf_static_offset +#if __has_attribute(preserve_static_offset) +#define __bpf_static_offset __attribute__((preserve_static_offset)) +#else +#define __bpf_static_offset +#endif +#endif + #ifndef __ksym #define __ksym __attribute__((section(".ksyms"))) #endif -- 2.56.0