Re: [PATCH] Fix C++ compilation on MinGW

[Orgad Shaneh <orgads at gmail dot com>]

On Tue, Nov 8, 2016 at 1:36 PM, Pedro Alves <palves@redhat.com> wrote:
>
> Hi,
>
> On 11/02/2016 09:53 AM, orgads@gmail.com wrote:
> > From: Orgad Shaneh <orgads@gmail.com>
> >
> > When compiling with MinGW, pyconfig.h renames hypot to _hypot.
>
> Yeah, that's not a good idea in C++.  We have a similar
> issue with gnulib's '#define foo rpl_foo' preventing use of
> "foo" as class methods etc.  Particularly annoying for "open",
> "close", etc.  (I plan to address that.)
>
> >
> > If math.h is included later, hypot is not declared correctly.
> >
> > When g++ is used, it has 'using ::hypot', which doesn't exist.
>
> So due to the define, that actually expanded to:
>
>  using ::_hypot;
>
> Right?
>
> Anyway, with your fix, IIUC, if someone adds a call to
> std::hypot somewhere (or uses the "hypot" symbol for
> something unrelated), we'll still have a problem.
>
> I'm thinking that the patch below might be a better fix.
> However, my cross mingw setup does not include Python, so I
> can't verify it works.
>
> WDYT?
>
> From 49f5b6892c959e9f1a3ea50240e8d83da63c6268 Mon Sep 17 00:00:00 2001
> From: Pedro Alves <palves@redhat.com>
> Date: Tue, 8 Nov 2016 10:48:32 +0000
> Subject: [PATCH] Fix Python hypot mingw
>
> ---
>  gdb/python/python-internal.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
> index 8545c7b..9d1a046 100644
> --- a/gdb/python/python-internal.h
> +++ b/gdb/python/python-internal.h
> @@ -88,6 +88,18 @@
>  /* Request clean size types from Python.  */
>  #define PY_SSIZE_T_CLEAN
>
> +/* When compiling with MinGW, pyconfig.h (included by other Python
> +   headers) renames hypot to _hypot.  That conflicts with C++'s
> +   std::hypot.  See <https://bugs.python.org/issue11566>.
> +
> +   In C++, it's not a good idea to define standard C functions as
> +   macros.  Fortunately, pyconfig.h has double-inclusion guards, so
> +   include it ourselves, and #undef any conflicting symbol it may have
> +   defined.  Note libstdc++'s <c...> headers also #undef C-inherited
> +   function-like macros, including "hypot".  */
> +#include <pyconfig.h>
> +#undef hypot
> +
>  /* Include the Python header files using angle brackets rather than
>     double quotes.  On case-insensitive filesystems, this prevents us
>     from including our python/python.h header file.  */
> --
> 2.5.5
>

Yes, this looks fine. Thanks!

- Orgad