Subject: Re: [Boost-build] Where in build are the OS names set
From: Edward Diener (eldiener_at_[hidden])
Date: 2014-07-08 02:39:04
On 7/8/2014 12:40 AM, Vladimir Prus wrote:
> On 07/08/2014 04:00 AM, Edward Diener wrote:
>> Where in Boost Build are the various OS names set that I see mentioned
>> in builtin.jam in the default-host-os local rule ( and a few other
>> places ) ?
>> I see such OS names as NT, MACOSX, LINUX etc. I am particularly
>> interested in how the OS is determined in Boost Build. One of the OS
>> is MINGW and I am interested to know how Boost Build determines that
>> the environment in which it is being used is MINGW under Windows.
> these macros do not determine runtime environment, they determine
> compilation environment. See
>> In trying to work out a solution for determining whether or not an
>> invocation of clang under Windows is using clang as built using MingW or
>> clang as built using VC++ the OS name of MINGW might be used to
>> distinguish between them if I can understand how it is determined. The
>> alternative I can think of is that the end-user must specify a command
>> which invokes clang-cl for VC++, otherwise it is clang as built using
>> MingW, but I would like to avoid this added burden on the end-user if
>> necessary when using clang under Windows.
> The problem is there are 3 variables:
> - The compiler that b2 was built with
> - The compiler that clang was built with
> - The execution environment - which is basically the shell where b2
> is invoked (either cmd.exe or mingw's sh.exe)
So the OS that is set is the compilation environment. That does not help
me since the end-user on Windows could create Boost Build with, let's
say, VC++ and still run the MingW version of clang when using clang as
the toolset using a library.
> For all I know, there's no strong correlation between those, so a way to
> explicitly specify how clang is build, or,
> otherwise, a way for clang to report how it was build, will be necessary.
> What does it even matter how clang was built?
The end-user on Windows will execute 'b2 toolset=clang' to invoke clang
as the toolset. This could mean clang as built with VC++ or it could
mean clang as built with MingW. They are two totally different build
environments, with their own subset .jam files invoked within the
general clang.jam. Clang as built with VC++ needs to use the
clang-win.jam file which I will add to Boost Build, while clang built
with MingW will use a very slightly modified clang-linux.jam file which
I can update in Boost Build. Even though both are clang under Windows
they are largely different environments as far as Boost Build is
concerned. The problem is how the end-user can distinguish between them
from within Boost Build so that the correct sub-clang jam file is used.
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