Date: Fri, 19 Feb 2016 16:50:40 -0800 From: Conrad Meyer <cem@FreeBSD.org> To: Benjamin Kaduk <bjkfbsd@gmail.com> Cc: Gleb Smirnoff <glebius@freebsd.org>, Alan Somers <asomers@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, Sergey Kandaurov <pluknet@gmail.com>, "src-committers@freebsd.org" <src-committers@freebsd.org> Subject: Re: svn commit: r295768 - head/usr.sbin/iostat Message-ID: <CAG6CVpUDWjSF6ht1hHKXp0PPh-H6zg51tace8=m0DEqdOrWGSA@mail.gmail.com> In-Reply-To: <CAJ5_RoCbWLUkwdRv4FeFVGpzCENooJbokH0SNXtiCeoRSeW%2BfQ@mail.gmail.com> References: <201602182008.u1IK81vg092127@repo.freebsd.org> <CAE-mSO%2B7p=Equq81PPQjfZv1piPydBr4Mnk363CEs3w9EXRi9w@mail.gmail.com> <CAOtMX2hyZ=GFgp8F6t0dMDYF5FSPdoP9KdMU7V5rmscpaPUnsw@mail.gmail.com> <20160219230612.GR1945@FreeBSD.org> <CAJ5_RoCbWLUkwdRv4FeFVGpzCENooJbokH0SNXtiCeoRSeW%2BfQ@mail.gmail.com>
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On Fri, Feb 19, 2016 at 3:14 PM, Benjamin Kaduk <bjkfbsd@gmail.com> wrote: > On Fri, Feb 19, 2016 at 5:06 PM, Gleb Smirnoff <glebius@freebsd.org> wrote: >> Isn't zero filling part of the standard? I don't see why lack of >> explicit zeroing is a warning? Looks a false warning to me. > > > It is not quite as simple as this would make it sound. The elements or > members of an aggregate (e.g.) structure type are initialized as if it were > an object of static storage duration (i.e., to zero) if the initializer list > does not contain enough initializers for all members of the aggregate type, > per item 21 of section 6.7.8 of n1256.pdf. However, such initialization > does not necessarily need to zero any padding bytes that are present, which > may take unspecified values. Personally, I think this particular clang > warning can be too aggressive, especially for complex structs, but on the > other hand given the indeterminateness of padding, bzero/memset are often a > better choice anyway. By definition, padding byte contents are unused. There is no reason their values matter one way or another, so why do we care about the distinction between bzero and member zero initialization? Best, Conrad
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