From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from cloud.peff.net (cloud.peff.net [104.130.231.41]) (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 22BA6372AB0 for ; Thu, 20 Nov 2025 08:16:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=104.130.231.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763626576; cv=none; b=mIMCM9ulBHZYCA77IwVsrSOjGZhpbp4lI+Tms2kOjZdykEYEvzXGLXWv5P4nm9NCivSfTK/rvc+0TjAeHKU3NVKDgNSc1tLdQPvRFk+vtvukhnBloktca98TFcirKzmme0JvDijY7oZWtKSgS05q5poJfUcgUBIEHU+GJb8vjTQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763626576; c=relaxed/simple; bh=bSJHhKW7OuHmLuLe/qsky51+p/yjMmii1hJYLa2vqS4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=qdcX5nCn+cW1dBNhvkxDIe9SfY5wco1dAfsRoG5CUjuFA62uFU9NGpM6Ka0mXqelob2H3qP2sqhYjIocg0YoGe/j/YvhAtH70jZmSNCyT0WxHJz6YH70sRABwxYHdRC9OaHHGQ9X5K4fSb6+yKJaeglZ6uNhUzh1tZz6ggpdxKQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=peff.net; spf=pass smtp.mailfrom=peff.net; dkim=pass (2048-bit key) header.d=peff.net header.i=@peff.net header.b=LOSj4Tqq; arc=none smtp.client-ip=104.130.231.41 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=peff.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=peff.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=peff.net header.i=@peff.net header.b="LOSj4Tqq" Received: (qmail 41713 invoked by uid 109); 20 Nov 2025 08:16:14 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed; d=peff.net; h=date:from:to:cc:subject:message-id:references:mime-version:content-type:content-transfer-encoding:in-reply-to; s=20240930; bh=bSJHhKW7OuHmLuLe/qsky51+p/yjMmii1hJYLa2vqS4=; b=LOSj4TqqEf05fMdjfld8NZ6zj/FM0YY+SvGrgOBgwkKdsGiLhKcijdBljyHPEwRosDbXDg+QbZ4Ddy+SOPh8hHARUy9dTj2mPRHk/9d5zLfKBTjYYXj7zf+IXNWGac2GsgjoI3IsTkVD1ZApOEVrMXcZnHVSNA3PfppB4KGqBrbvJVoz3E5Nap+ps4QXYuFlWDEujrnPM+oQGTXoTxtk5nntd2D4vhYmv0Zmsux/wS6LpdVbPX6MKKJFmpbpd7h8w/SSR9zO3Appl2NsudHWxMvrOeSrHDKN/ETeXUfY5MUsQzgStNjMwJeMKh92Ot5YgrAIdfGu1nRoa73qFDrdnQ== Received: from Unknown (HELO peff.net) (10.0.1.2) by cloud.peff.net (qpsmtpd/0.94) with ESMTP; Thu, 20 Nov 2025 08:16:13 +0000 Authentication-Results: cloud.peff.net; auth=none Received: (qmail 62462 invoked by uid 111); 20 Nov 2025 08:16:16 -0000 Received: from coredump.intra.peff.net (HELO coredump.intra.peff.net) (10.0.0.2) by peff.net (qpsmtpd/0.94) with (TLS_AES_256_GCM_SHA384 encrypted) ESMTPS; Thu, 20 Nov 2025 03:16:16 -0500 Authentication-Results: peff.net; auth=none Date: Thu, 20 Nov 2025 03:16:11 -0500 From: Jeff King To: Anders Kaseorg Cc: rsbecker@nexbridge.com, Kristoffer Haugsbakk , Toon Claes , git@vger.kernel.org Subject: Re: t8020-last-modified.sh failure on s390x (Re: [PATCH v4] last-modified: implement faster algorithm) Message-ID: <20251120081611.GC1283645@coredump.intra.peff.net> References: <20251023-b4-toon-last-modified-faster-v3-1-40a4ddbbadec@iotcl.com> <20251103154726.26592-1-toon@iotcl.com> <4dc4c8cd-c0cc-4784-8fcf-defa3a051087@mit.edu> <3b24b6a3-61cc-4b9a-a823-f1e58fd9919b@app.fastmail.com> Precedence: bulk X-Mailing-List: git@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Nov 19, 2025 at 12:06:35PM -0800, Anders Kaseorg wrote: > On 11/19/25 05:49, Kristoffer Haugsbakk wrote: > > On Wed, Nov 19, 2025, at 12:34, Anders Kaseorg wrote: >> > > t8020-last-modified.sh is broken on the s390x platform in v2.52.0. > >> Bisection implicates commit >> 2a04e8c293766a4976ceceb4c663dd2963e0339e > “last-modified: implement >> faster algorithm” [1]. > > Does > `./t8020-last-modified.sh --verbose` give any interesting > output? > I quoted that output in my previous message. The failures in subtests 16 and > 19 come with these diffs: > > --- expect    2025-11-19 11:28:57.966106204 +0000 > +++ actual    2025-11-19 11:28:58.110112543 +0000 > @@ -1,2 +1,2 @@ > +ac29b6e974b49803f1c6ec5a705d1bf7dbfa7d2f m1.t >  m2 m2.t > -m1 m1.t > > […] > > --- expect    2025-11-19 11:29:03.492349022 +0000 > +++ actual    2025-11-19 11:29:03.648355864 +0000 > @@ -1,2 +1,2 @@ > -b5 file2 > -b2 file > +da1857e0652b6f264c0038d684ddecddc273e506 file2 > +da1857e0652b6f264c0038d684ddecddc273e506 file Interestingly, the commits it returns are merges. E.g., here is the state after test 16: $ git log --oneline --graph * ac29b6e (HEAD) Merge tag 'm1' into HEAD |\ | * 53e7187 (tag: m1) m1 * | 9b81a41 (tag: m2) m2 |/ * 08525b6 (master) remove a * 664d121 (tag: 3) 3 * a732b0c (tag: 2) 2 * 1edf6f6 (tag: 1) 1 Though it is also the first commit we start traversing from. The same is true after test 19 (da1857e is the tip of HEAD there). So I am not sure if the bug is "we are not passing down blame from the merge", or just "we are not passing down blame at all". I can't help but notice that this same failure is seen on s390x and HP NonStop[1], both of which are (I think) big-endian. And not on any of our usual little-endian platforms. I don't see anything that looks questionable in terms of casting or integer handling in the patch that introduced the problem, though. Probably a long shot, but if you are able to build with "make SANITIZE=address,undefined" and re-run t8020, that would let us check for endian-specific memory access issues. -Peff [1] https://lore.kernel.org/git/003901dc596c$40bfbd80$c23f3880$@nexbridge.com/