Wireshark · Wireshark-dev: Re: [Wireshark-dev] Use of variadic macros

[Guy Harris <guy@xxxxxxxxxxxx>]

> On Oct 4, 2015, at 7:41 AM, Peter Wu <peter@xxxxxxxxxxxxx> 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@xxxxxxxxx> 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).