[Pam-developers] [Fwd: Re: GCC 6 -Wnonnull is too aggressive]
Apparently our usage of __nonnull__ attribute is not completely aligned
with what gcc developers mean with it. Use of the attribute declares
that the parameter can never be NULL which means that the checks in the
IF_NO_PAMH for example can be removed by the compiler during the
optimization. We would need to remove the __nonnull__ attribute or at
least add -fno-delete-null-pointer-checks to the default CFLAGS.
I'd prefer removing the __nonnull__.
What do you think?
Tomas
-------- Forwarded Message --------
From: Jonathan Wakely <jwakely(a)fedoraproject.org>
Reply-to: Development discussions related to Fedora
<devel(a)lists.fedoraproject.org>
To: Development discussions related to Fedora <devel(a)lists.fedoraprojec
t.org>
Subject: Re: GCC 6 -Wnonnull is too aggressive
Date: Fri, 19 Feb 2016 12:30:58 +0000
On 19/02/16 10:49 +0100, Petr Spacek wrote:
The thing is that some developers (e.g. me and ISC :-)) do not think
that
assert() should be used only in debug builds.
E.g. BIND itself is written in "Design by contract" spirit and
asserts are
used all over the place to make sure that code which does not behave
as
intended is killed as soon as possible (and thus prevented from doing
collateral damage). Call it defensive programming if you wish.
That's fine. Don't use attribute((nonnull)) then.
It's illogical to promise the compiler that something will never,
ever, ever be null, but also check whether it's null. If you're not
100% certain it can't be null, then you lied to the compiler. If you
are 100% certain it can't be null then the assert is redundant and can
be removed.
If you're only 99.999% certain, and so the assert serves a useful
purpose, then don't make promises that you can't keep.
If you just want to advise the compiler that something *probably*
won't be null, and tell it to optimize based on that assumption, then
you can use __builtin_expect() to provide that hint (although I
wouldn't actually recommend doing so).
Don't make a promise when you mean to give a hint.
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Tomas Mraz
No matter how far down the wrong road you've gone, turn back.
Turkish proverb
(You'll never know whether the road is wrong though.)