[cfe-dev] Compiling a simple Win32 program

[Michael Spencer]

On Wed, Jun 13, 2012 at 5:09 AM, Nikola Smiljanic <popizdeh at gmail.com> wrote:
> I think there is more than one issue here.
>
> These things are still unclear to me:
> 1. If both VS and MinGW are installed, which toolchain should Clang use and
> how to decide?

I would like to follow the principle of least surprise here. What do
users expect? MSVC has a well established way of picking the toolchain
to use based on bat files but I'm not sure how MinGW users are used to
dealing with multiple versions of the toolchain. There's also no
precedent for a tool that can work with either.

> 2. How to obtain the target triple once we've selected the toolchain? Right
> now Clang selects the toolchain based on the default target triple (comming
> from config.h when Clang is compiled).

This is similar to the issues above. What does the user expect? Again
MSVC uses bat files, and I have no idea how MinGW handles this.

I feel that basing this choice on how clang was compiled is the wrong
way to do it, as we currently end up often making the obviously wrong
choice.

> 3. How to decide what the target platform is when using either mingw-w64 or
> multiple mingw installations? For VS, toolchains for different targets are
> in different directories and this is easy to detect, but I don't know how
> this exactly works for MinGW/MinGW-W64. I think they have an executable for
> every target?

Isn't this exactly the same as choosing the target triple? Also I
assume by platform you only mean x86 vs x86-64.

> Things I do know, at least partially:
> - If multiple versions of VS are installed, Clang will select the first one
> in the PATH.

It's actually currently a lot more complicated than this. First it
adds %INCLUDE%, then it tries %VCINSTALLDIR%, then it tries the
registry to pick the highest version, then it uses
%VS{80|90|100}COMNTOOLS% depending on the version it was compiled
with, then any of them. And that's just for the VS paths. It then goes
and looks for the Windows SDK in the registry, which is already added
to %INCLUDE% by vcvars.bat. So we actually end up with multiple
versions of MSVC on the path. However the link.exe it picks is always
the first one on the path, which always uses %LIB% to look for
libraries.

This clearly needs to be cleaned up :P.

> - Same logic should apply for multiple MinGW/MSYS versions. "which gcc"
> should give back the active toolchain. The question about the target still
> remains.

I agree in part. I do however wonder how we would handle a distro of
MinGW that completely removes gcc in favor of clang.

> - In the case of VS the target is decided based on the toolchain's directory
> (the one in VC\bin targets x86, etc.)

The target is decided by the binary yes, but the headers and libs are
decided by %INCLUDE% and %LIB%.

> A bit unrelated issue is the one about MinGW toolchain support inside Clang
> codebase, or the lack thereof. This is why the hardcoded paths are still
> needed in InitHeaderSearch. This is something that needs to be done, I had a
> look into it but never found enough time to do something useful. I think
> this is the first thing to work on If you're interested in better MinGW
> support. For more info look
> here http://lists.cs.uiuc.edu/pipermail/cfe-dev/2012-March/020235.html (see
> reply from Chandler).

Agreed that this all goes in the driver. But selecting the exact
version to use is a bit more complicated than with gcc on Linux. At
least from what I've seen.

> As for the external text files, I don't think a feature like that could be
> implemented without discussing it first with larger community. Just
> something to take into account if you had any plans to work on something
> like this. This is just my personal impression after following the list for
> some time :)

There is a strong aversion to text config files for toolchains unless
absolutely necessary.

- Michael Spencer

> On Wed, Jun 13, 2012 at 10:15 AM, Mikael Lyngvig <mikael at lyngvig.org> wrote:
>>
>> I suggest that you don't hardwire the info into the tool but rather make
>> an external text file with a list of places to search or something.  Once I
>> get around to it, I was planning to look into eliminating the hardwired
>> paths from Clang because they are only marginally useful on Windows and are
>> very likely to cause all sorts of unexpected behavior - if, for instance,
>> the user has multiple version of Mingw installed (I have both Mingw32 and
>> Mingw64 installed).  Luckily, I decided to name my Mingw32 installation
>> that: C:\Mingw32.  Otherwise, Clang would have made use of Mingw32 features
>> even though it was built as a 64-bit compiler that should only make use of
>> Mingw64.  Perhaps a new option, "-basedir" or something, should be added so
>> the user can explicitly specify what directory to use as the base directory
>> for include file and library searches.
>>
>>
>> 2012/6/13 Nikola Smiljanic <popizdeh at gmail.com>
>>>
>>> MinGW users should be in the clear since GnuWin32 only collides with
>>> link.exe from VS, or so I think. The question is how to decide whether to
>>> search for msvc or mingw, but this is where the default triple comes into
>>> play?
>>>
>>>
>>> On Wed, Jun 13, 2012 at 9:59 AM, Mikael Lyngvig <mikael at lyngvig.org>
>>> wrote:
>>>>
>>>> Hehe, what if the user prepends the GnuWin32 tools or MSYS to the path
>>>> AFTER having run vcvarsall.bat?  Anyway, I figure that most LLVM users are
>>>> bright enough that they'll figure it out quickly.
>>>>
>>>>
>>>> 2012/6/13 Michael Spencer <bigcheesegs at gmail.com>
>>>>>
>>>>> On Tue, Jun 12, 2012 at 8:09 PM, Mikael Lyngvig <mikael at lyngvig.org>
>>>>> wrote:
>>>>> > Just be aware that GnuWin32 includes a link.exe command, which
>>>>> > creates
>>>>> > symbolic or hard links (not sure which).  It is part of GNU
>>>>> > coreutils.  So
>>>>> > if the user sets up an environment to use GnuWin32 and Mingw32, so as
>>>>> > to be
>>>>> > able to run the llvm test suite, you'll bug into this one.
>>>>>
>>>>> vcvars prepends it's paths to PATH, so it will not find gnuwin32 or
>>>>> mingw/msys link.
>>>>>
>>>>> - Michael Spencer
>>>>>
>>>>> > 2012/6/12 Nikola Smiljanic <popizdeh at gmail.com>
>>>>> >>
>>>>> >> It will search the path to find the first link.exe. The one from
>>>>> >> Visual
>>>>> >> Studio should be first if Command prompt or vcvars.bat are used.
>>>>> >>
>>>>> >>
>>>>> >> On Tue, Jun 12, 2012 at 2:23 PM, Kim Gräsman <kim.grasman at gmail.com>
>>>>> >> wrote:
>>>>> >>>
>>>>> >>>
>>>>> >>> That sounds like it would match my expectations for behavior, good
>>>>> >>> idea!
>>>>> >>>
>>>>> >>> Can you have it fall back on %PATH% if no VS environment variables
>>>>> >>> are
>>>>> >>> found?
>>>>> >>>
>>>>> >>> Thanks,
>>>>> >>> - Kim
>>>
>>>
>>
>>
>>
>> --
>> -- Love Thy Frog!
>
>