Re: [boost] [build] Problems with VC14 and MSPDB140.DLL (was: [testing][teeks] MSVC-14 errors about MSPDB140.DLL)

Subject: Re: [boost] [build] Problems with VC14 and MSPDB140.DLL (was: [testing][teeks] MSVC-14 errors about MSPDB140.DLL)
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2015-08-10 19:42:45

Mere moments ago, quoth I:
> On 11/08/2015 06:35, Andrey Semashev wrote:
>> I have tried to add this echo and indeed it outputs the broken Path
>> already. Also, I tried to print %PATH% from the console (VS2015 x86
>> x64 Cross Tools Command Prompt) and it also has the %DevEnvDir% path
>> first there.
>>
>> I inspected the vcvarsx86_amd64.bat script which sets up the
>> environment and I can see that in line 62 it indeed inserts
>> %DevEnvDir% before the paths to the compilers, so we have our culprit.
>> The question is what do we do about it?
>
> One question is why Boost is trying to load the cross tools rather than
> the native x64 compiler.
>
> While it's not unheard of to want to build 64-bit code from a 32-bit
> build machine, the vast majority of cases will be the reverse, so the
> native compilers should be preferred unless explicitly requested otherwise.
>
> (Recent stats say that 92% of new Windows machines are 64-bit; older
> machines have a higher percentage of 32-bit but it's very likely that
> developers, at least, will have 64-bit machines by now.)

Ok, examining msvc.jam I think I've found the issue.  It defaults to 
"x86_amd64" (cross compiler), and then swaps this to "amd64" (native 
compiler) if the environment variable PROCESSOR_ARCHITECTURE is set to 
AMD64.

However this will only be the case if the process executing the jam file 
is also 64-bit.  A 32-bit process running under WOW64 will see "x86" for 
that environment variable, just like it would on 32-bit Windows.

So, either Boost.Build itself needs to be a 64-bit process, or it needs 
to be more clever at detecting a 64-bit architecture even as a 32-bit 
process.  The simplest way of doing the latter is to read 
PROCESSOR_ARCHITEW6432, which will be unset for native 32 or 64-bit and 
set to AMD64 on 32-bit WOW64.  (ie. the jamfile should assume native 
64-bit if either of PROCESSOR_ARCHITECTURE or PROCESSOR_ARCHITEW6432 are 
set to AMD64.)