From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta0.migadu.com (out-188.mta0.migadu.com [91.218.175.188]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A51E023B63E for ; Wed, 10 Jun 2026 03:45:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781063128; cv=none; b=OPvtGm9u3dY4WAFPMlkKpeywOtiO2Vmin9xXuLlhlqz9EUzQOJpQlI1x7wPgcqyPtjujV0UGK5U5xThq3gOvG+GvI48xvEKQt8tC3n9QezF2lYRd9dF0vREFIXIQPhUa32P5LWq4SFolCSDaSHC5Risav9JQ8IzBIqXaEfxW5lA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781063128; c=relaxed/simple; bh=gwJWGz77qe/1ByjH2crEmxFB0VTpP5Uh8us4EGeuVZs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=EDNOYKycblTBorNcBJhSJZYrlvomP1SAmyqh9BmqvxUUHLPyGFHWmpbjWJBktQSJJr5ptdtlxDB6E3rLI5fdiH3Oo6s0UnlEsbRC3aX6th2xtaNceuEJhVgQNdlDStS7Thxu9nCmFpdDJ6/+m19LaelJM+h0YdlaJti97i0HdQA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=M8qYx/uU; arc=none smtp.client-ip=91.218.175.188 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) header.d=linux.dev header.i=@linux.dev header.b="M8qYx/uU" Message-ID: <811b9cd4-829e-4a02-8265-ea0f64d7991f@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1781063122; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=5ukLTOUrZY9TshkkY0HnPkd3VQYy5ImvpCPeKTGUyn8=; b=M8qYx/uUxrM/7AaNOj8lkJJRx4Gw+6O0m3ls2e9R2ZXe1tMmfoOpzzdbv1KRoaJOKojXTS WU+a6/yOln06iVRWj6iPGSrL+dLVyZf9Xuwi7xnW2pY/R1fCQvsvy99OtcLa+uq4N0yF1O ZRIYyksfovSbR2kC/TkimCQDxDhLrkU= Date: Tue, 9 Jun 2026 20:45:13 -0700 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v2 1/2] selftests/bpf: Keep int return type for tailcall subprogs Content-Language: en-GB To: bot+bpf-ci@kernel.org, bpf@vger.kernel.org Cc: ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, kernel-team@fb.com, martin.lau@kernel.org, eddyz87@gmail.com, clm@meta.com, ihor.solodrai@linux.dev References: <20260609233407.2711577-1-yonghong.song@linux.dev> <5ece679164a4c99cbba93f55c2f9609be6e315d4813737a15b083c9f7dffa17f@mail.kernel.org> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: <5ece679164a4c99cbba93f55c2f9609be6e315d4813737a15b083c9f7dffa17f@mail.kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 6/9/26 5:07 PM, bot+bpf-ci@kernel.org wrote: >> diff --git a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf2.c b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf2.c >> index ce97d141daee..c4fadee5aadc 100644 >> --- a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf2.c >> +++ b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf2.c > [ ... ] > >> diff --git a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy2.c b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy2.c >> index ae94c9c70ab7..6fde0ab92148 100644 >> --- a/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy2.c >> +++ b/tools/testing/selftests/bpf/progs/tailcall_bpf2bpf_hierarchy2.c >> @@ -25,8 +25,11 @@ int count1 = 0; >> static __noinline >> int subprog_tail0(struct __sk_buff *skb) >> { >> + int ret = 0; >> + >> bpf_tail_call_static(skb, &jmp_table, 0); >> - return 0; >> + barrier_var(ret); >> + return ret; >> } >> >> __auxiliary >> SEC("tc") >> int classifier_0(struct __sk_buff *skb) >> { >> count0++; >> subprog_tail0(skb); >> return 0; >> } > The patch adds barrier_var() to subprog_tail0() to prevent the compiler > from optimizing its return type from int to void. However, is the > approach sufficient for classifier_0()? > > Looking at how the patch handles other callers like classifier_1(): > >> @@ -41,16 +44,22 @@ int classifier_0(struct __sk_buff *skb) >> static __noinline >> int subprog_tail1(struct __sk_buff *skb) >> { >> + int ret = 0; >> + >> bpf_tail_call_static(skb, &jmp_table, 1); >> - return 0; >> + barrier_var(ret); >> + return ret; >> } >> >> __auxiliary >> SEC("tc") >> int classifier_1(struct __sk_buff *skb) >> { >> + int ret; >> + >> count1++; >> - subprog_tail1(skb); >> + ret = subprog_tail1(skb); >> + __sink(ret); >> return 0; >> } > In classifier_1(), the return value is captured and passed to __sink(). > This creates a use at the callsite that forces the compiler to preserve > the int return type. > > Without capturing and sinking the return value in classifier_0(), could > LLVM still create a void-returning clone of subprog_tail0() for this > specific callsite? While subprog_tail0() is also called from > tailcall_bpf2bpf_hierarchy_2() where its return value is properly sunk, > the compiler might still specialize the function differently for the two > callsites. We should be fine. In the same file, we have  SEC("tc") __success __retval(33) SEC("tc") int tailcall_bpf2bpf_hierarchy_2(struct __sk_buff *skb) { int ret = 0, ret1, ret2; clobber_regs_stack(); ret1 = subprog_tail0(skb); ret2 = subprog_tail1(skb); __sink(ret1); __sink(ret2); __sink(ret); return (count1 << 16) | count0; } This will guarantee subprog_tail0() will have a return value. > > [ ... ] > > > --- > AI reviewed your patch. Please fix the bug or email reply why it's not a bug. > See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md > > CI run summary: https://github.com/kernel-patches/bpf/actions/runs/27243286945