Re: autoconf + automake support for MSVC

[Bruno Haible]

Peter Rosin wrote:
> From time to time, I'm wondering if reusing *-*-mingw* for cl is the
> right decision.

I think so, yes. mingw and msvc share the same kernel, the same object file
format, and large parts of the C library.

But it definitely ought to be documented, because it is very non-obvious
(if you know that mingw came after winnt, and Emacs has a winnt port).

> The main benefits that I see are that you don't have to
> cross compile if you are in MSYS

You have the wrong notion of "cross compile", if you think cross-compiling
means that $host != $build. When I am building for i386-pc-linux-gnu from
a x86_64-pc-linux-gnu machine, I am *not* cross-compiling. When you are
building for i586-pc-mingw32 from i586-pc-cygwin, you are *not* cross-
compiling. Cross-compiling means that the generated executable can not be
run on the build machine.

It can be necessary to use cygpath also when not cross-compiling. Gladly,
the Automake emitted build uses it, and the 'compile' script from the
Automake 'msvc' branch uses it as well.

> > I use Cygwin as a build environment.
> 
> But then you are in the 'fake' cross territory (according to the terminology
> of the libtool manual), which is also not always desirable. E.g., if you use
> absolute path names (I'm sure you try to avoid them) and Libtool, you need
> to tell Libtool that you are faking the cross compile with an extra configure
> argument:
> 
>       lt_cv_to_tool_file_cmd=func_convert_file_cygwin_to_w32
>
> See http://www.gnu.org/s/libtool/manual/libtool.html#Cygwin-to-MinGW-Cross

I am not faking a cross-compile; I am not cross-compiling at all.
Libtool needs to be fixed to use cygpath when needed, without requiring an extra
configure argument. That configure argument is implicit from $host and $build.

> MSYS is doing all the faking for you

It does it in a buggy way. I pass the argument "/dev/null" to a program, and
the MSYS execve call silently converts it to "nul" (or vice versa, I don't
remember). That's not reliable, because not all program arguments are meant
to be file names. To do it correctly, file name conversions need to be explicit.
That's what cygpath is for.

Bruno
-- 
In memoriam Sergei Tretyakov <http://en.wikipedia.org/wiki/Sergei_Tretyakov>