Date: Mon, 28 May 2018 18:24:06 +0000 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Ravi Pokala <rpokala@freebsd.org> Cc: arch@freebsd.org Subject: Re: To assert() or not to assert(), that is not really a question... Message-ID: <22469.1527531846@critter.freebsd.dk> In-Reply-To: <4427091E-3B0E-4C34-B4C6-3557DD7B55E4@panasas.com> References: <4514.1527319154@critter.freebsd.dk> <4427091E-3B0E-4C34-B4C6-3557DD7B55E4@panasas.com>
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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.
>> =
>> ...
>> =
>> 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
-- =
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe =
Never attribute to malice what can adequately be explained by incompetence=
.
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