Date: Mon, 20 Feb 2017 19:35:20 -0500 From: Pedro Giffuni <pfg@FreeBSD.org> To: cem@freebsd.org Cc: src-committers <src-committers@freebsd.org>, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r313982 - in head/sys/dev: agp al_eth an arcmsr bce beri/virtio bhnd/cores/usb buslogic ce cm cp ctau cx de ed fatm fe firewire hptiop hptmv iicbus isp le md ncr netmap ofw patm pccard ... Message-ID: <1d213a3f-ea84-256c-e08b-e5e100ef83ba@FreeBSD.org> In-Reply-To: <CAG6CVpUSxaQkq%2B7siKQPOW4FuaVpoY5uMcSb6jMvrROqSiqzGA@mail.gmail.com> References: <201702200343.v1K3hCk3060716@repo.freebsd.org> <CAG6CVpUSxaQkq%2B7siKQPOW4FuaVpoY5uMcSb6jMvrROqSiqzGA@mail.gmail.com>
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Hello; Just been discussing the same issue in private as well ... On 2/20/2017 6:40 PM, Conrad Meyer wrote: > On Sun, Feb 19, 2017 at 7:43 PM, Pedro F. Giffuni <pfg@freebsd.org> wrote: >> Author: pfg >> Date: Mon Feb 20 03:43:12 2017 >> New Revision: 313982 >> URL: https://svnweb.freebsd.org/changeset/base/313982 >> >> Log: >> sys/dev: Replace zero with NULL for pointers. >> >> Makes things easier to read, plus architectures may set NULL to something >> different than zero. > Hi Pedro, > > I like the change for style reasons. > > The comment about architectures with non-zero NULL is a little > misleading, though. This change has no impact on non-zero bit pattern > NULL architectures. The zero pointer value in C is NULL and NULL is > the zero pointer value in C. It may have a bit pattern other than > zero (i.e., printf("%p", NULL) may be non-zero and memset(&p, 0, > sizeof(p)) is bogus in portable code) but assigning the logical zero > value is always legitimate. Grrr ... yes the comment is/was misleading: I would undo it if I didn't have to revert the commit with it. Other project have SVN configured to permit changing the log message BTW. > After all, NULL is just a casted zero value: > > #define NULL ((void *)0) The compiler is pretty good at detecting when the value is a pointer though. The change has few (if any) effect on real life but coming from the days where most computer languages were somewhat stronger typed I really like to be able to distinguish between a zero valued pointer and a zero valued int. > Maybe this is moot. I don't believe any architecture FreeBSD actually > supports has non-zero bitpattern NULL, but something weird like CHERI > might. Such "weird" platforms are starting to appear: https://reviews.llvm.org/D26196 Regards, Pedro.
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