Build portability: enable or disable warnings

[Kelly O'Hair]

On May 16, 2011, at 7:23 AM, Dr Andrew John Hughes wrote:

> I think the issue is actually having -Werror enabled for all builds, not
> just debug builds.  Without that, these additional warnings would just be
> noise.  Having -Werror on also causes problems just upgrading the version
> of gcc, regardless of distro-specific patching, as new warnings are
> introduced or old ones reclassified.
> 
>> Andrew.


The code being compiled is different with debug vs. product builds due to assert logic, so I consider it
important that all builds use -Werror if they use it at all.

The -Werror option is a blessing and a curse. I find it highly commendable that teams (like 
hotspot) have taken a 'no warnings allowed' approach to their code base, more teams should do this.
Given the critical nature of a VM in the JDK, it only makes sense to take all precautions in verifying the code is correct.

But it only makes 100% sense when using the same compiler, same compiler version, and on the same system.
For hotspot, you should be able to get rid of -Werror  by setting WARNINGS_ARE_ERRORS to empty.

I've wondered if we need to put a little more smarts in determining what situations (compiler&os) warrant
adding the -Werror, but at the same time if it is a valid warning, maybe the behavior we have is right.
So my attitude up to this time has been that new ports should use WARNINGS_ARE_ERRORS=
to start, but eventually they should fix these warnings before a port is finished.
(And I use the term 'port' very loosely here, a new version of gcc is a port to me).

I've been involved in running some of the commercial static analysis tools and seeing what
they complain about, and there is an overlap between some of the compiler warnings and what
these tools are spitting out as 'critical issues'.
I find it amusing that a 20+ year old C/C++ compiler might have been issuing warnings about some
questionable code for a long time, but it takes an expensive purchased static analysis tool to say the
same thing and all of a sudden it's a "critical must fix issue".
In any case, I've always taken compiler warnings seriously, but the different behaviors between all
the different compiler implementations can be very frustrating when using options like -Werror.

-kto

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