From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 66-220-155-178.mail-mxout.facebook.com (66-220-155-178.mail-mxout.facebook.com [66.220.155.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CD3C2372EF3 for ; Thu, 8 Oct 2026 07:50:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=66.220.155.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791445823; cv=none; b=A7168zh7Ybn6qTK0N2X1x6wZbRBEvR8fbkqTzlcLZotoQ0fB5ki1XLL7RXKl9/V22Dn8unsjs6nmq/uwoW6h0LZe/SonAL+ZE3t3QVkESQGThWPRk6X/ihXFquMczZ/ll+d3owbVW4MU1ZeNlLGIv6Idigs1Fsi6t91sxELbDCY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791445823; c=relaxed/simple; bh=gbjkncN7SLGd+gQsE8W6q7Ky6A4jYqERu8bqU3x0SuY=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=g3O7uO9yQ0cBIPHvwjR5KVe34KTca43MfvVv5DRXqIq4gO7zX8/Vi2K68c572E+RrLfjQ03LRs69S52eLzSlqgeoo40eOcJHK/3S6Q8bnUzMcMN8eDiCpnGZA2eJaDTSfWh83O5I3QGL6gYNffJxpdR3ivKjjFy6I+CkqynfmXQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=fail smtp.mailfrom=linux.dev; arc=none smtp.client-ip=66.220.155.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=linux.dev Received: by devvm16039.vll0.facebook.com (Postfix, from userid 128203) id 0980B2FDA0BD20; Thu, 8 Oct 2026 00:50:15 -0700 (PDT) From: Yonghong Song To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Eduard Zingerman , kernel-team@fb.com Subject: [PATCH bpf-next v9 03/23] bpf: Add the bpf_unwind() and bpf_unwind_resume() kfuncs Date: Thu, 8 Oct 2026 00:50:15 -0700 Message-ID: <20261008075015.2996034-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261008074959.2993751-1-yonghong.song@linux.dev> References: <20261008074959.2993751-1-yonghong.song@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable An exception cleanup needs two terminators: - bpf_unwind() begins an unwind: the frames it leaves run their landing pads on the way out to the program's exit. It is separate from bpf_throw(), which discards the frames in between. - bpf_unwind_resume() ends a landing pad, carrying the unwind on. The compiler calls it _Unwind_Resume, which a later libbpf patch resolves to this name, and passes it the exception object, which the kfunc takes as ptr__ign. Neither is registered yet: that waits for the patch that dispatches pads at run time. Signed-off-by: Yonghong Song --- kernel/bpf/helpers.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c index a284f20c97d5..4eccd6742eba 100644 --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -3424,6 +3424,10 @@ static bool bpf_stack_walker(void *cookie, u64 ip,= u64 sp, u64 bp) return false; } =20 +__bpf_kfunc void bpf_unwind(void) +{ +} + __bpf_kfunc void bpf_throw(u64 cookie) { struct bpf_throw_ctx ctx =3D {}; @@ -3445,6 +3449,16 @@ __bpf_kfunc void bpf_throw(u64 cookie) WARN(1, "A call to BPF exception callback should never return\n"); } =20 +__bpf_kfunc void bpf_unwind_resume(void *ptr__ign) +{ + /* + * Never reached: the verifier accepts this kfunc only as a frame + * terminator and bpf_do_misc_fixups() lowers every one of them to + * 'r0 =3D 0; exit', so no call to this body survives to run. + */ + WARN_ONCE(1, "exception cleanup resume was not lowered to a return\n"); +} + __bpf_kfunc int bpf_wq_init(struct bpf_wq *wq, void *p__const_map, unsig= ned int flags) { struct bpf_async_kern *async =3D (struct bpf_async_kern *)wq; --=20 2.53.0-Meta