Date: Sat, 22 Feb 2020 09:25:18 -0700 From: Ian Lepore <ian@freebsd.org> To: Kyle Evans <kevans@FreeBSD.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r358248 - head/sys/vm Message-ID: <a3b2125de10d214d6e422d183f1fdc7e0e38e014.camel@freebsd.org> In-Reply-To: <202002221620.01MGK46E072303@repo.freebsd.org> References: <202002221620.01MGK46E072303@repo.freebsd.org>
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On Sat, 2020-02-22 at 16:20 +0000, Kyle Evans wrote: > Author: kevans > Date: Sat Feb 22 16:20:04 2020 > New Revision: 358248 > URL: https://svnweb.freebsd.org/changeset/base/358248 > > Log: > vm_radix: prefer __builtin_unreachable() to an unreachable panic() > > This provides the needed hint to GCC and offers an annotation for readers to > observe that it's in-fact impossible to hit this point. We'll get hit with a > a -Wswitch error if the enum applicable to the switch above were to get > expanded without the new value(s) being handled. > > Modified: > head/sys/vm/vm_radix.c > > Modified: head/sys/vm/vm_radix.c > ============================================================================== > --- head/sys/vm/vm_radix.c Sat Feb 22 13:23:27 2020 (r358247) > +++ head/sys/vm/vm_radix.c Sat Feb 22 16:20:04 2020 (r358248) > @@ -208,8 +208,7 @@ vm_radix_node_load(smrnode_t *p, enum vm_radix_access > case SMR: > return (smr_entered_load(p, vm_radix_smr)); > } > - /* This is unreachable, silence gcc. */ > - panic("vm_radix_node_get: Unknown access type"); > + __unreachable(); > } > > static __inline void What does __unreachable() do if the code ever becomes reachable? Like if a new enum value is added and this switch doesn't get updated? -- Ian
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