Date: Mon, 28 May 2018 13:07:35 -0700 From: Ravi Pokala <rpokala@freebsd.org> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: <arch@freebsd.org> Subject: Re: To assert() or not to assert(), that is not really a question... Message-ID: <40636EBA-9D41-4F3E-8D10-3654E92FC6AA@panasas.com> In-Reply-To: <22469.1527531846@critter.freebsd.dk> References: <4514.1527319154@critter.freebsd.dk> <4427091E-3B0E-4C34-B4C6-3557DD7B55E4@panasas.com> <22469.1527531846@critter.freebsd.dk>
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Interesting stuff. Thanks, phk! -Ravi (rpokala@) =EF=BB=BF-----Original Message----- From: Poul-Henning Kamp <phk@phk.freebsd.dk> Date: 2018-05-28, Monday at 11:24 To: Ravi Pokala <rpokala@freebsd.org> Cc: <arch@freebsd.org> Subject: Re: To assert() or not to assert(), that is not really a question.= .. -------- In message <4427091E-3B0E-4C34-B4C6-3557DD7B55E4@panasas.com>, Ravi Pokala = writ es: >> 1. "Regular asserts" - things which are just plain wrong, which >> probably means we have a genuine bug somewhere. Examples could >> be null pointers where previous checks should have ensured this >> not be so. Also error situations for which there is no saner >> handling that killing the projcess. >>=20 >> ... >>=20 >> 3. "wrong asserts" - Internal state is messed up, program flow >> has taken a "impossible" branch. A good example is the >> default branch of a switch on a finite input set. > >Hi Poul-Henning, > >I am in strong overall agreement with your argument. I am however >confused as to how (1) and (3) are different; they're both irrevocably >bad internal state. The regular assert is assert() as we know and love it, and if it triggers it reports the C-source of the failing condition. The WRONG macro always triggers, and reports its string argument. Here is a random snippet of varnish code showing both: /* Per specification */ assert(sizeof vpx1_sig =3D=3D 5); assert(sizeof vpx2_sig =3D=3D 12); [...] p =3D req->htc->rxbuf_b; if (p[0] =3D=3D vpx1_sig[0]) i =3D vpx_proto1(wrk, req); else if (p[0] =3D=3D vpx2_sig[0]) i =3D vpx_proto2(wrk, req); else WRONG("proxy sig mismatch"); Poul-Henning PS: You can explore the Varnish source code here: https://github.com/varnishcache/varnish-cache Asserts defined in: .../include/vas.h Custom backtrace/state dump in: .../bin/varnishd/cache/cache_panic.c Code coverage results: http://varnish-cache.org/gcov/ You may also find the void-pointer paranoia interesting: .../include/miniobj.h --=20 Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe =20 Never attribute to malice what can adequately be explained by incompetence.
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