From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.gentoo.org (woodpecker.gentoo.org [140.211.166.183]) (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 0E972BE6C; Sat, 7 Sep 2024 10:14:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=140.211.166.183 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725704086; cv=none; b=QA52Q4ovP80SOL7FERYRm1AXLQH0NlK8j//TTHeF9Kw8KS+vRBO0nB48JzP+fYoiNVXMCosl3iL1+emSyIV3k6najOatEesgxyiW3OAYv+1MMr9aczXKhSdMwoNHRJ6RDbefPocfGlek+jsf7oVsiYLmlSgeZ4uiIRoMOpX9OuU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725704086; c=relaxed/simple; bh=JT92TKwiGMMqxUOypsYQl8r9Varrf0PHpmosFXha8Tw=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=HLMFm6c9M2AW8CNO3pFHmmkLUeVVvoB3h56Y/MIMv8F6WGo9Oc2+CLb/dSotSxKjv5Mdie0x+s5PxDQf65tn+M32tU6UOg0DCTXhz8PT3Qw2J3cLy4aAe75PvIXca80OsUP9YCgXKam/BnR04HfcNHZs1A2SAWkL5FfVmmE1hb4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gentoo.org; spf=pass smtp.mailfrom=gentoo.org; arc=none smtp.client-ip=140.211.166.183 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gentoo.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gentoo.org From: Sam James To: Masahiro Yamada Cc: Nathan Chancellor , Nicolas Schier , linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] fixdep: handle short reads in read_file In-Reply-To: (Masahiro Yamada's message of "Sat, 7 Sep 2024 11:02:44 +0900") Organization: Gentoo References: <3132727fea08e81e834104761b5a5630d337340a.1725636560.git.sam@gentoo.org> Date: Sat, 07 Sep 2024 11:14:40 +0100 Message-ID: <87y143ixdb.fsf@gentoo.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Masahiro Yamada writes: > On Sat, Sep 7, 2024 at 12:29=E2=80=AFAM Sam James wrote: Hi Masahiro, >> >> 50% or so of kernel builds within our package manager fail for me with >> 'fixdep: read: success' because read(), for some reason - possibly ptrac= e, >> only read a short amount, not the full size. >> >> Unfortunately, this didn't trigger a -Wunused-result warning because >> we _are_ checking the return value, but with a bad comparison (it's comp= letely >> fine for read() to not read the whole file in one gulp). >> >> Fixes: 01b5cbe7012fb1eeffc5c143865569835bcd405e > > > Fixes: 01b5cbe7012f ("fixdep: use malloc() and read() to load dep_file > to buffer") > Ah, thanks. I'll fix that and send v2 depending on how we decide to move forward wrt below. > > I guess, another approach would be to use fread() instead of read(). > > Does the attached diff fix the issue too? > > Unfortunately no. It failed for me in the same way as before :( The man page mentions: > On success, fread() and fwrite() return the number of items read or > written. This number equals the number of bytes transferred only when siz= e is 1.=20=20 so I guess it suffers from the same pitfall. I checked POSIX & ISO C as well which says: > If a partial element is read, its value is unspecified. and > The fread() function shall return the number of elements successfully > read, which shall be less than nitems only if an error or end-of-file > is encountered, or size is zero. The error reference is kind of mysterious there though. It kind of looks like fread *should* work. I'll send this mail and then think about it a bit later and ask around to see if I'm missing something obvious? > [...] thanks, sam