Re: Use of variadic macros

[Guy Harris <guy () alum mit edu>]

> On Oct 4, 2015, at 7:41 AM, Peter Wu <peter () lekensteyn nl> wrote:
>
> On Thu, Oct 01, 2015 at 10:15:12AM -0700, Guy Harris wrote:
> > On Oct 1, 2015, at 9:53 AM, Alexis La Goutte <alexis.lagoutte () gmail com> wrote:
> >
> > > Yes, there is a "warning" with GCC from some month...
> > >
> > > ../../epan/proto.h:2740:54: warning: anonymous variadic macros were introduced in C99 [-Wvariadic-macros]
> >
> > Perhaps we need to turn on the "use C99" flag for some compilers,
> > including, but not limited to, GCC-compatible compilers, to suppress
> > warnings or even errors.
>
> The feature seems supported even in c90 mode on gcc 5.2.0 and clang
> 3.7.0. After reading the gcc manual page, I've decided to settle with
> -Wno-variadic-macros.

And, from 2012:

        https://www.wireshark.org/lists/wireshark-dev/201209/msg00144.html

where "they" refers to variadic macros:

> They're supported with Microsoft's compilers at least as far back as Visual Studio 2005:
>
>       http://msdn.microsoft.com/en-us/library/ms177415(v=vs.80).aspx
>
> There's no earlier version of the documentation offered by the "Other Versions" dropdown, but I don't know whether 
> that means "earlier compilers, such as MSVC 6, didn't support them" or "we don't have the MSVC 6 documentation 
> online".  This page:
>
>       http://bytes.com/topic/c/answers/220087-macros-variable-parameter-list-ms-vc-compiler-6-0-a
>
> has a claim that MSVC 6 didn't support variadic macros.  If that's the case, I don't personally have a problem with 
> kicking MSVC 6 to the curb; we may already have done so in the documentation, as
>
>       http://www.wireshark.org/docs/wsdg_html_chunked/ChToolsMSChain.html
>
> only mentions it when it says "The official Wireshark 1.8.x releases are compiled using Microsoft Visual C++ 2010 
> SP1. The official 1.2, 1.4, and 1.6 releases are and were compiled using Microsoft Visual C++ 2008 SP1. Other past 
> releases, including the 1.0 branch, were compiled using Microsoft Visual C++ 6.0.", and doesn't at all discuss using 
> MSVC++ 6.
>
> I don't know what other compilers, such as Sun C^WOracle Solaris Studio, HP's ANSI C compiler, or IBM's XL C support. 
>  My *guess* is that older versions of those compilers may not have supported them but that they've all up-to-date 
> with C99 features.
>
> Sun C fully supported C99 as of Sun Studio 12 (not to be confused with Sun Studio, Memphis :-)):
>
>       http://docs.oracle.com/cd/E19205-01/820-4155/c.html#about
>
> *if* you specify -xc99; I don't know whether it or later versions support variadic macros without -xc99 or whether 
> earlier versions supported them.
>
> IBM C for AIX fully supported C99 as of V6.0 in 2002:
>
>       
> http://www-01.ibm.com/common/ssi/cgi-bin/ssialias?infotype=an&subtype=ca&supplier=897&appname=IBMLinkRedirect&letternum=ENUS202-161
>
> and XL C for AIX
>
>       http://www-01.ibm.com/software/awdtools/xlcpp/aix/features/
>
> supports C99 now (with no indication in the document of when it started, but the Wikipedia page for C99, whence I got 
> these references, says it started with V11.1).  I don't know whether either of them have separate C89 and C99 modes 
> (which they might, for the benefit of those developing code that needs to build on C89 compilers) or whether, in C89 
> mode, they support extensions such as variadic macros.  Given that one of IBM's compilers is the reason why we ban // 
> comments - it disallows them by default - I suspect that, when not running in C99 (or C11?) mode, they do not support 
> them.
>
> The HP ANSI C compiler supports C99 at least as of A.06.25
>
>       http://h21007.www2.hp.com/portal/download/files/unprot/aCxx/Online_Help/getstarted.htm
>
> I don't know whether it has separate C89 and C99 modes (which they might, for the benefit of those developing code 
> that needs to build on C89 compilers) or whether, in C89 mode, it supports extensions such as variadic macros.
>
> > P.S. Are there any other C99 features that we forbid that are actually
> > supported by supposedly C89-only compilers like MSVC?
>
> // comments are, I think, supported by MSVC; I don't know whether any UN*X C compilers support them without being 
> told to run in C99 or C11 (or "GCC compatible"?) mode.
>
> Turning on "full C99" mode for compilers does run the risk of people using C99 features *not* supported by MSVC++ and 
> not having them discovered until the build breaks.

At this point, given Microsoft's apparently-renewed interest in C99, I'd say we should, for all compilers, turn on 
whatever flags are needed to support variadic macros and // comments, and if that means not catching some C99 features 
not supported by MSVC++ prior to the latest version, so be it.

So, yeah, let's go for -Wno-variadic-macros.  I may try running the 2.0-rc1 source tarball through the compilers on The 
Written Word's machines and, if anything breaks, see if there are compiler flags that need to be turned on.

> Patch is at https://code.wireshark.org/review/10781

I've reviewed it +2 and submitted it, so it should be in 2.0-rc1 (or rc0 or whatever Gerald calls it).

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