Date: Wed, 18 May 2016 17:58:10 -0600 From: Ian Lepore <ian@freebsd.org> To: Bruce Evans <brde@optusnet.com.au> Cc: Gleb Smirnoff <glebius@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r300167 - in head: contrib/bsnmp/snmpd usr.sbin/bsnmpd/bsnmpd Message-ID: <1463615890.1180.306.camel@freebsd.org> In-Reply-To: <20160519092734.U1798@besplex.bde.org> References: <201605182202.u4IM2JF7047307@repo.freebsd.org> <1463609665.1180.301.camel@freebsd.org> <20160519092734.U1798@besplex.bde.org>
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On Thu, 2016-05-19 at 09:43 +1000, Bruce Evans wrote: > On Wed, 18 May 2016, Ian Lepore wrote: > > > On Wed, 2016-05-18 at 22:02 +0000, Gleb Smirnoff wrote: > >> Log: > >> Revert r299830, it has couple of fatal errors. > >> > >> The CMSG_ family of macros take care of alignment, so we don't > need > >> r299830 > >> at all, even if it was correct. Put NO_WCAST_ALIGN into > Makefile. > > The breaks detection of cast-align bugs elsewhere in the program. > > > So all of this was about a "cast increases required alignment" kind > of > > warning for a macro that takes care of alignment? Wouldn't the > proper > > fix then be to change CMSG_DATA() so that its internal cast is > void* > > instead of unsigned char* (he asked, knowing Bruce would come along > > soon and point out why that's a dumb question)? > > I don't know much about CMSG*, so I wouldn't have if you didn't ask : > -). > > Changing its type might expose bugs. Kernel code mostly casts it so > would get the same cast-align error if that were enabled in the > kernel. > netinet6 passes it to a function without an explicit cast. The > function > does an implicit conversion to a struct pointer and there should be a > different warning for that. char * and u_char * are required to be > binary compatible with void *, but it is bad style to depend on that. > > So void * works better in all cases in the kernel. > > LINUX_CMSG_DATA() already returns void *. > > Bruce > For some reason I had assumed a (void*) cast would wish away the warning about increasing alignment (without losing that warning at other places in that code). Now I can't say for sure why I thought that would be so, but it does seem to me I've fixed warnings like that by casting through void* as an intermediate type. But maybe that was a different situation/different warning. -- Ian
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