From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 66-220-144-179.mail-mxout.facebook.com (66-220-144-179.mail-mxout.facebook.com [66.220.144.179]) (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 6F62A38BF8D for ; Thu, 1 Oct 2026 13:30:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=66.220.144.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790861425; cv=none; b=YpSGKsQQLAoeEqx8+Slv6DOqtrr6lDHT2itoPfKRUfmSEocuWz/YExR7ZVlazhARla9d8Mj1lNdGScOMaTDIQ/Loj/u0nj0+2w6vTgCZfa5rYBIuRjNwag8ZxewiRwrmxhgrB85C3Glm0qVR+T6dx7/mK22EBrnOkBRhwNdDmgY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790861425; c=relaxed/simple; bh=PLSD6+NmYu+26TPKD2YfIBv6U+FkjHvllNuK8HLAH5s=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=pxKBmBqXW1iDDE5BJ8LiBDbN1kQo1RNOcH4DDKC/a95thoWbaKh1d3BQjzrL/9eEZcgUU1y0xjBmSDw+EkhMCZPx0oEZwUg5DGHKkDaWO1qHafBSVUH7bt5TqR9FyqY9/tOUlicPL/DIVXYwqmZRBk8Zf+LFr2/O7WYkdx7um60= 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=66.220.144.179 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 160502E6E0B87E; Thu, 1 Oct 2026 06:30:22 -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 v8 03/22] bpf: Add the bpf_unwind() and bpf_unwind_resume() kfuncs Date: Thu, 1 Oct 2026 06:30:22 -0700 Message-ID: <20261001133022.1337350-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261001133006.1335369-1-yonghong.song@linux.dev> References: <20261001133006.1335369-1-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, and the kernel provides both = as kfuncs so that a BPF program can name them. 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 keeps its own meaning -- leaving for the exception boundary with th= e frames in between discarded. bpf_unwind_resume() ends a landing pad, carrying the unwind on once that frame's cleanups have run. The compiler names it _Unwind_Resume, the base unwind ABI's entry point for the same thing; a later libbpf patch resolve= s that name to this one. Every unwind ABI hands _Unwind_Resume the exceptio= n object, and LLVM emits that argument on BPF too. Nothing in the kernel needs it now, but the kfunc takes it as ptr__ign so the prototype matches the call the compiler makes. Both are defined here and neither is registered with any program type yet= . bpf_unwind() may appear wherever a program can unwind from, and bpf_unwind_resume() only inside a landing pad, and neither does anything until a pad can be dispatched at run time, so registration waits for the patch that adds that. 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