linux-kernel - Re: [PATCH] objtool: Don't use -Werror

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Date:   Fri, 5 Apr 2019 11:15:41 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Luis Ressel <aranea@...ah.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        open list <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH] objtool: Don't use -Werror

On Fri, Apr 05, 2019 at 06:05:50PM +0200, Luis Ressel wrote:
> On Fri, Apr 05, 2019 at 09:39:26AM -0500, Josh Poimboeuf wrote:
> 
> > Hm, I would actually argue the reverse.  Warnings are generally bad and
> > -Werror is useful for ensuring that we don't have any.  For warnings
> > that don't provide value, we just disable those individual warnings.
> 
> Sure, during development it's an excellent idea to investigate compiler
> warnings, and -Werror can be useful for that. But the Linux kernel is
> built by countless users in wildly varying environments, and it's almost
> a given that someone will use a compiler that'll complain about a valid
> part of your code whose style it considers bad.

Maybe so, but objtool only supports two compilers: GCC and clang.  And
only one version of libelf ;-)

> As an example, the warning that's breaking the build for me is -Wundef
> complaining about several "#if UNDEFINED_IDENTIFIER" constructs in the
> libelf headers. (I agree with gcc in considering this bad style, but
> it's perfectly valid C, and there probably wasn't a warning about it
> back when this header was written.)

I consider that a good thing, because I *want* the build to be broken
when somebody uses a bad version of libelf.  A patch to produce a more
useful error message (e.g., "bad version of libelf") would be welcome of
course.

If/when we get to the point where there's a valid use case for warnings
in the objtool build, I would consider this patch.  But we don't seem to
be there yet.

-- 
Josh