[Numpy-discussion] 64bit infrastructure

Ondřej Čertík ondrej.certik@gmail....
Wed Aug 22 11:46:03 CDT 2012


On Wed, Aug 22, 2012 at 8:50 AM, David Cournapeau <cournape@gmail.com> wrote:
> On Wed, Aug 22, 2012 at 4:12 PM, Ondřej Čertík <ondrej.certik@gmail.com> wrote:
>> On Wed, Aug 22, 2012 at 7:35 AM, Travis Oliphant <travis@continuum.io> wrote:
>>> On Aug 22, 2012, at 9:28 AM, David Cournapeau wrote:
>>>
>>>> On Wed, Aug 22, 2012 at 3:25 PM, Travis Oliphant <travis@continuum.io> wrote:
>>>>>
>>>>> On Aug 22, 2012, at 3:59 AM, Ralf Gommers wrote:
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Aug 21, 2012 at 12:51 AM, Travis Oliphant <travis@continuum.io>
>>>>> wrote:
>>>>>>
>>>>>> I'm actually not sure, why.   I think the issue is making sure that the
>>>>>> release manager can actually "build" NumPy without having to buy a
>>>>>> particular compiler.
>>>>>
>>>>>
>>>>> That would help, yes. MS Express doesn't work under Wine last time I checked
>>>>> by the way.
>>>>>
>>>>> However, the issue is more than just one license. There's a large number of
>>>>> packages that depend on numpy and provide binaries. If they can't make those
>>>>> compatible with numpy ones, that's a problem. Users will first install numpy
>>>>> 64-bit, and then later find out that part of the scientific Python stack
>>>>> isn't available to them anymore.
>>>>>
>>>>>
>>>>>
>>>>> As far as I understand, you don't *have* to build all downstream
>>>>> dependencies with the same compiler that NumPy was built with unless your
>>>>> extension relies on the way C-functions pass structures on the stack (not
>>>>> pointers to them, but structures as a whole) or if it relies on the
>>>>> representation of FILE*.      At one time all structures were passed as
>>>>> pointers specifically for this reason.   The FILE* situation is a problem,
>>>>> but most extensions don't use NumPy C-API calls that have a FILE* argument.
>>>>
>>>> It is much more pervasive than that, unfortunately. And for fortran,
>>>> it is much worse, because if we build scipy or numpy with Intel
>>>> Fortran, I think we pretty much force everyone to use intel fortran
>>>> for *any* binary on top of them.
>>>
>>> Can you be more specific?   Does the calling convention for C-routines created with Intel Fortran differ so much?
>>
>>
>> I have the same question as Travis. If you are interested about ABI
>> for Fortran, I have created this FAQ:
>>
>> http://fortran90.org/src/faq.html#are-fortran-compilers-abi-compatible
>>
>> Since NumPy only calls the Fortran routines, but does not expose them,
>> then the only issue is how to build NumPy with (let's say) Intel
>> Fortran. That's a separate issue.
>> Once NumPy is built, then nobody cares, because they only need to
>> interface the C routines, if anything at all.
>>
>> As far as Fortran runtime library goes (which of course is different
>> for Intel and gfortran), I am currently not sure whether it is
>> possible to mix them, but I think you probably can, if numpy .so is
>> using Intel, and my own .so is using gfortran.
>>
>>
>> Finally, if NumPy is build using MSVC, does this force everybody to
>> use the same C compiler? I thought that C compilers are ABI
>> compatible, at least Intel C and gfortran C are ABI compatible.  Is
>> MSVC different?
>>
>> Btw, to correctly call Fortran from C, one should always be using the
>> iso_c_binding module, as explained here:
>>
>> http://fortran90.org/src/best-practices.html#interfacing-with-c
>>
>> Then the Fortran code becomes just like any other C library.
>
> It is unfortunately more complicated than that.
>
>  1 regarding fortran runtimes: I have never been able to link a
> gfortran object file with Visual Studio linker (link.exe).

You cannot mix the Fortran object .o files between compilers.
That will never work, because Fortran compilers are not ABI
compatible, see the FAQ.

The only way this could work is if you can mix gcc .o file with MSVC
linker (I don't
know if this is possible or not). If that works,
then you should be able to use iso_c_binding in Fortran to produce
gcc's compatible .o
file and then link it.

Which errors were you getting when linking it? Was it a problem with
libgfortran runtime
(that you of course need to link as well)? This runtime can be a problem.

>  2 mixing runtimes is never a good idea, because it becomes difficult
> to avoid passing a pointer from one runtime to the other. Intel
> fortran compiler obviously knows how to deal with the C runtime of
> Visual Studio, but gfortran doesn't.

By Fortran runtime I mean this library in my Ubuntu:

	libgfortran.so.3 => /usr/lib/x86_64-linux-gnu/libgfortran.so.3
(0x00007ffaa9ce9000)

Here
are all the libraries in my typical gfortran program:

	linux-vdso.so.1 =>  (0x00007ffffe9ff000)
	libgfortran.so.3 => /usr/lib/x86_64-linux-gnu/libgfortran.so.3
(0x00007ffaa9ce9000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007ffaa99ef000)
	libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007ffaa97d8000)
	libquadmath.so.0 => /usr/lib/x86_64-linux-gnu/libquadmath.so.0
(0x00007ffaa95a2000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007ffaa91e5000)
	/lib64/ld-linux-x86-64.so.2 (0x00007ffaaa022000)

What exactly is the C runtime? libc?

The only way to make Fortran talk to C, in a robust and supported way,
is to use the iso_c_binding, which makes gcc talk to gfortran
and Intel Fortran to Intel C/C++.

So if gcc can talk to MSVC, so should gfortran.
Can you be more specific what does not work (if you know)?
That would be a good thing to put in my FAQ.

>  3 gcc and visual studio are ABI compatible in a (very) restricted
> sense: they share the same calling convention at least in C, but
> that's pretty much it. Because having multiple copies of a runtime is
> so common on windows, you cannot easily pass objects between dlls.
> Travis mentioned FILE*, but that's also true for pointers returned by
> malloc, file descriptors, etc... See this for example:
> http://stackoverflow.com/questions/1052491/c-runtime-objects-dll-boundaries

That seems to be a C issue. So if that can be resolved, I *think* that Fortran
should work too.

>
> Because of 1, if we have a binary with intel + visual studio, we are
> effectively forcing everyone on windows to use intel fortran
> compilers. I would rather have the official binaries using open source
> toolchains.

I don't want to force other people either to use Intel Fortran.

But I still don't understand why I could not use gfortran and gcc for
my program,
that links against numpy (that uses let's say Intel Fortran internally).

I don't have access to Intel Fortran on windows, but I am available to
help with this issue.

Ondrej


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