Re: [boost] Compiling with Clang 3.7.0 from windows

Subject: Re: [boost] Compiling with Clang 3.7.0 from windows
From: Edward Diener (eldiener_at_[hidden])
Date: 2015-09-04 15:56:53

On 9/4/2015 2:38 AM, Vladimir Prus wrote:
> On 04-Sep-15 1:32 AM, Edward Diener wrote:
>
>>> It would be nice if we could discover some easy steps to run the
>>> official clang 3.7 binary on an official "mingw-build" or "mingw-w64"
>>> build and configure user-config.jam correctly.
>>
>> It needs far more Boost build/bjam expertise for the clang-linux.jam
>> than I am able to provide. I know what would need
>> to be done but I have no idea how to do it within Boost build.
>
> Could you start by documenting, say on Trac or GitHub Wiki, what needs
> to be done? As it stands, I'm not even clear which of zillion mingw
> flavours to install.

I can not document on Github Wiki, trac, and on this mailing list what 
needs to be done. I will gladly discuss what I know here.

>
>> Essentially for any given clang release the Boost build toolset for
>> clang on Windows ( remember that clang-linux.jam
>> supports both clang on Linux and clang on Windows targeting gcc )
>> needs both the directory where the clang version
>> resides and the directory where the target mingw(-64)/gcc version
>> resides. These directories needed to be prepended to
>> the Windows PATH for all Boost build actions such as compile/link/run
>> etc.
>
> - Why do you need clang in PATH? Is the compiler not able to find other
> component relative to itself?

It is possible that clang does not need to be on the PATH, but I always 
add it to the beginning of the PATH anyway. I do know absolutely that 
when you attempt to use mingw(-64)/gcc directly that it's 'bin' 
directory must be on the PATH for gcc to even compile/link correctly. If 
clang can work without it's 'bin' directory being on the PATH that is 
great, but I take the conservative, safe way.

>
> - If clang needs mingw, it seems reasonable to document that mingw must
> be in PATH, and that the user must add such
>    settings on Windows?

Is that a question or an assertion ?

As I mentioned in a previous post the --sysroot option may be a way for 
using a particular mingw(-64) distribution, without needing that 
distribution to be on the PATH, but I have never tried it. It was 
mentioned to me by someone on the clang developer's mailing list. As 
usual, in regard to clang, it is barely documented.

>
> - If one has mingw with both 32 and 64 bit support, can one use it with
> clang, with -m32 and -m64 options both working?
>    (If not, that seems like a huge bug in clang)

Mingw only has 32-bit support so I assume you mean mingw-64. The 
mingw-64 distributions offer separate distributions for 32-bit and 
64-bit builds. So for any gcc release you are installing 32-bit and 
64-bit distributions in separate directory trees.

Clang can work with either 32-bit or 64-bit code using -m32 and -m64 
respectively, but it needs to "use" a 32-bit or 64-bit mingw-64/gcc 
release accordingly.

The upshot of all this is that it may be possible to compile/link with 
clang and a target mingw(-64)/gcc without any PATH manipulation at all ( 
using --sysroot ). But unless one is creating a module with complete 
static linking there will be dependencies on mingw(-64)/gcc DLLs when 
running, So my own preferrred solution very conservatively puts the 
clang clang 'bin' first in the PATH followed by the mingw(-64)/gcc 'bin' 
next in the PATH, before invoking any Boost build functionality.