From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=91.218.175.33 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793901671; b=gcaeRU7oBI4MXTbmAfwWDQuliARPv9p7mrCpLCx4+9ZJlZpbZzfYEOUxHV+OdgYYzVJn 2r7jiinIimQjc2bH2LqKwiwovrhtShAv/cp7dCcAs5u48lSp1dZEgMB2c7vMOzcERJvUp CM1QRojA7mSofa5oRQXi9hZy8Z+4QKnvLAlB/UxGb2XYZtFLOCJymVDWE3WVeqhVwJe2P 4ZuUBy8y6SrGpTq7tV9G1Rl91Ix49E4pf2i4YPGZTo83+5PGPXtfRqzaB5nFPgzG+HHdS KhmR3kXW1/iu1cGtCO5qXU+dWQva01d386X4VsY3evBlUeS/xbNnzfQ3O++5kpFFJpg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793901671; 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=mqIgipGNH3uaJPun3gY2EdWJe5EjgNO1lxAnDZz0bLo=; b=A1L5gO6d2XIatDfhKRhct+Jpktr+clnJlwAPph5odNvgwJOIufrNfVxFM9dMPuKJAHI3 RDsylOEMsSpbDoWPqRLFjxIrYNVmuW5FWEgca5JUNwXwJyxxu57Ae5/oqCEOgCMsc/kX6 xJUED+CwCexiK8rc8bE44kkxcoRZnbPDuD2AaJYg4ZRZ2nAdgYy+doTUngFjofdzcAKyC Bm/EIXgDOedKR03jSczYbC+ZT7ikkD1GeWO0oRme4s0FJ/MxJv1IEp+aA5L1oNRJP4oqn hOWQlVkyBhPI6BKuEZcu9yNQ2fZcG9QPe3ec9LyyQb/nqUfKuUEXHjeQb7I8lRbhOkA== 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=sx+6tTot; arc=none smtp.remote-ip=91.218.175.33 Received: from mta0.migadu.com (out-33.mta0.migadu.com [91.218.175.33]) (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 49700606A31B for ; Thu, 5 Nov 2026 18:01:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 49700606A31B 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=sx+6tTot X-Envelope-To: bpf@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=BGAG7nspM85fYkrguaFEyaMIhs8lFjlVYZzb9T0jeG8=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1793901668; v=1; x=1794506468; b=sx+6tTotw++m0p8vqHKsVo9Sj5cdXGOiLPfmmpxNtCeJw+KgiTIjfk101A5tA920yNgGBcK6 4k0boHuXZmmX/hAvlFSTrE+kHJMwe7Xo4QksWpcOnezgp+3l8c/gTz5o0n8Rk1LCY+MCJD1qCrn g771EPrJNzRcXRUTslKpiRPI= X-Envelope-To: bpf@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id eae9d1363d87049d; Thu, 05 Nov 2026 18:01:08 +0000 X-Mizu-Trace-ID: eae9d1363d87049d 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 v4 12/17] bpftool: Emit __bpf_static_offset on verifier-rewritten context types Date: Thu, 5 Nov 2026 10:58:40 -0700 Message-ID: <20261105175845.30357-13-ihor.solodrai@linux.dev> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261105175845.30357-1-ihor.solodrai@linux.dev> References: <20261105175845.30357-1-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 these 13 types in vmlinux.h through a __bpf_static_offset macro. 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. LLVM main has the fix [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 d913723a691a..1329745c5854 100644 --- a/tools/bpf/bpftool/btf.c +++ b/tools/bpf/bpftool/btf.c @@ -1206,12 +1206,17 @@ 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; } @@ -1264,6 +1269,13 @@ 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