Re: [PATCH 0/5] Remove a few hurdles of compiling with clang

[Andrew Pinski <pinskia@gmail.com>]

On Mon, Jun 12, 2017 at 8:54 AM, Simon Marchi <simon.marchi@polymtl.ca> wrote:
> On 2017-06-12 16:35, Eli Zaretskii wrote:
>>
>> That's not the issue: AFAIU, GDB already builds with clang.
>>
>> The issue is how much effort would we want to invest for that, and
>> what are we willing to give up when using GCC to be able to use other
>> compilers.  For example, the proposed patch adds an explicit "-x c++"
>> switch to _all_ compilations, and also tweaks the warning switches.
>> I'm not sure we want GCC builds to be affected so that clang builds
>> could be cleaner.  But maybe we have a policy about this which deems
>> these issues acceptable?
>
>
> Hi Eli,
>
> I included in this patchset the changes that I think improve the situation
> with Clang, but are neutral to GCC, so I don't think these should pose any
> problem.  Here is what I have to say about each patch:
>
>  - gdb: Pass -x c++ to the compiler: GCC (and even the Intel compiler)
> supports this option too, at worst it's a neutral change for compiling with
> GCC.

Why is this needed?  Why can't you use clang++ or similar to force
compiling as C++?

>
>  - gdb: Use -Werror when checking for (un)supported warning flags: it just
> forces the behavior to what's already the default with GCC.  Again, it's
> neutral at worst, at best it protects us if GCC ever decides to change its
> default behavior.


Yes I think this is ok because gcc also does not warn about
unsupported warning flags unless there is an error.

>
>  - gdb: Add -Wno-mismatched-tags: We already have a system that tests which
> warning flags are supported by the current compiler, so this flag will not
> be included in the builds with GCC.  So it's neutral for GCC, and improves
> the situation for Clang with almost no effort.

This warning is a bug in clang and really should not be warned about
in either -Wall or -Wextra.  I have been complaining about this since
clang added this option.

>
>  - linux-low: Remove usage of "register" keyword: That's a good legacy code
> cleanup in any case, IMHO.

Yes and no.  I don't think register was deprecated in C++11.

>
>  - Add ATTRIBUTE_PRINTF to trace_start_error: It's actually a legit warning,
> I'm surprised GCC itself doesn't warn about that.

This warning does not make sense.  Can you give some more context?

Thanks,
Andrew

>
> But I think it's a good thing to discuss how far we're willing to go to make
> GDB build cleanly with Clang, because some other issues are not so easily
> resolved.  Some warnings are a bit silly and don't provide much value (e.g.
> [1] or -Wmismatched-tags), so it may not make sense to go too far out of our
> way to make it happy.
>
> I think it's also good to have this discussion because of how relevant Clang
> is nowadays.  A big number of software developers are on OS X/macOS, on
> which Clang is the default compiler (shipped with Xcode).  Making the source
> more Clang-friendly removes a barrier to them contributing to GDB.
>
> Simon
>
> [1] https://bugs.llvm.org//show_bug.cgi?id=22712#c1