Date: Thu, 9 Aug 2018 15:46:14 -0600 From: Warner Losh <imp@bsdimp.com> To: Benjamin Kaduk <bjkfbsd@gmail.com> Cc: "cem@FreeBSD.org" <cem@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r337535 - head/sbin/init Message-ID: <CANCZdfqFg08GHUuzXWA0P6z6K9BPC07BW=Ki9OSbi4Cqk%2B6xyA@mail.gmail.com> In-Reply-To: <CAJ5_RoC5s-oVrkPx%2BCcF5oRhzqYniGcaF6hEZN7oFLonrV7Vfw@mail.gmail.com> References: <201808091217.w79CH3gO096411@repo.freebsd.org> <CAJ5_RoBVWZgMgoNGkTkCMB9kU5Ci1GcN-p_Ad-FMMwhO%2BQX5VA@mail.gmail.com> <CAG6CVpU8jwQJiNsf6B5Gq75QHEoGaT4K-dCK6Drc59ETPH4VRw@mail.gmail.com> <CAJ5_RoC5s-oVrkPx%2BCcF5oRhzqYniGcaF6hEZN7oFLonrV7Vfw@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Thu, Aug 9, 2018 at 3:41 PM, Benjamin Kaduk <bjkfbsd@gmail.com> wrote: > On Thu, Aug 9, 2018 at 11:03 AM, Conrad Meyer <cem@freebsd.org> wrote: > >> On Thu, Aug 9, 2018 at 5:52 AM, Benjamin Kaduk <bjkfbsd@gmail.com> wrote= : >> > On Thu, Aug 9, 2018 at 7:17 AM, Edward Tomasz Napierala < >> trasz@freebsd.org> >> > wrote: >> >> Use NULLs instead of casted zeroes, for consistency. >> > >> > It's probably helpful to note explicitly that these are not in >> arguments to >> > varargs functions, >> >> I don't think it's helpful. >> >> > in which case the explicit cast is needed in order to produce a progra= m >> that >> > will have >> > correct behavior on all compliant compilers/systems. >> >> Here "compliant" means "minimally compliant to the C standard." Use >> of NULL in varargs is functionally correct on all FreeBSD systems. >> >> > (We do define NULL to >> > be a zero-with-cast, >> > but programs >> >> (Ones that care about portability to weird systems.) I don't think >> BSD's 500 line init =E2=80=94 hyper local to FreeBSD =E2=80=94 is a stro= ng candidate >> for portability. >> >> > should not assume that NULL will be of pointer type -- "An >> > integer constant >> > expression with the value 0, or such an expression cast to type void *= , >> is >> > called a null pointer constant".) >> >> Right. The problem only arises when both conditions are met: >> >> 1. The system's varargs representation is smaller than the pointer >> representation, and >> 2. The runtime headers do not defined NULL as a pointer-typed value. >> (3. The function being invoked is actually varargs?) >> >> Neither is true on FreeBSD and v7-style init is not a useful place to >> call for portability. >> > > I don't really feel a need to continue the discussion that was already > started in response > to r336835 (in addition to the current thread), so I'll limit myself to > asking whether we > want to be writing standard C or a FreeBSD-specific dialect of C. My > understanding was > that we had some experience with the latter (e.g., heavy patching of the > compiler) and > it ended up with us in a bad place, which would tend to support writing > standard C or > as close to it as we can. (Yes, I know that we have non-standard printf > specifiers and the like.) > The conventional wisdom is code as close to the standard(s) as we can, but not to the point of insanity. If there's a good reason to deviate, that's OK so long as it's intentional and the deviation makes sense. For example, we calloc a bunch of stuff, but that's not a strictly standards conforming way to initialize pointers to be NULL. While c->ptr =3D 0 is always standar= ds conforming, memset(&c->ptr, 0, sizeof(c->ptr)); isn't. Yet we do this everywhere because we know we'll never run on an architecture where the bitwise representation of a NULL pointer isn't all 0's. There's dozens of other similar examples. Warner
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CANCZdfqFg08GHUuzXWA0P6z6K9BPC07BW=Ki9OSbi4Cqk%2B6xyA>