[issue28542] document cross compilation

[Xavier de Gaye]

Change by Xavier de Gaye :


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nosy:  -xdegaye

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[issue28542] document cross compilation

[Xavier de Gaye]

Xavier de Gaye added the comment:

Yes, I was not aware of DESTDIR. The 2.7 README contains also useful 
information on the build process, for example about some use cases of the 
'*shared*' entries in the Setup files (for when setup.py cannot detect/build an 
extension module) or about the '*static' entries (to be able to profile 
extension modules). It also explains Setup.local whereas the only information 
on Setup.local in the Python3 documentation, is restricted to 
https://docs.python.org/3/extending/extending.html#compilation-and-linkage :(

There is also a lot of noise in the 2.7 README, this possibly explains the 
trimming. Maybe the cross-build section in the 3.6 README could be a link to a 
new build section in the documentation ?

> --prefix etc are already mentioned in “./configure --help”

The documentation on sys.prefix and sys.exec_prefix gives details about where 
go which files which is useful when trying to figure out where to copy the 
files on the target after a cross-build.

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[issue28542] document cross compilation

[Martin Panter]

Martin Panter added the comment:

Actually I think it is good to document DESTDIR (you weren’t seem aware of it 
before?). I was just pointing out that it is useful to more than just Android. 
Perhaps Guido shouldn’t have trimmed it from the 2.7 readme (original text: 
https://hg.python.org/cpython/diff/988b3e807043/README). On the other hand, 
--prefix etc are already mentioned in “./configure --help”, and more people 
already seem to know about it.

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[issue28542] document cross compilation

[Xavier de Gaye]

Xavier de Gaye added the comment:

About 2.7, this is a list of the issues I am aware of, that may have to be 
fixed also in 2.7 (and 3.5 for some of them): issues #26884 #27434 #28444 and 
#22724. Issue #28589 was entered today and is a duplicate of the previous one.

> FWIW, DESTDIR, --prefix, etc are not specific to cross compilation or Android.

I must be seeing everything through my little Android hammer these days :)
This new patch removes the last paragraph.

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Added file: http://bugs.python.org/file45319/readme_5.patch

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[issue28542] document cross compilation

[Martin Panter]

Martin Panter added the comment:

Regarding 2.7, I guess it depends on your definition of “support”. People have 
been cross-compiling Python 2.7 longer than I have been working on Python. In 
the past I have tried to apply cross compilation fixes to 2.7. But if you are 
only confident about 3.6, let’s just stick with that for the moment.

FWIW, DESTDIR, --prefix, etc are not specific to cross compilation or Android. 
DESTDIR is also useful when building a package/tarball or whatever, rather than 
installing directly. And --prefix would be useful if you don’t have root access 
and want to install to $HOME or somewhere. These settings are mentioned in the 
2.7 README, but it looks like Guido trimmed them out for Python 3.0 (revision 
07d67a9725a7).

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[issue28542] document cross compilation

[Xavier de Gaye]

Xavier de Gaye added the comment:

New patch, less verbose and taking into account the previous posts.

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Added file: http://bugs.python.org/file45294/readme_4.patch

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[issue28542] document cross compilation

[Xavier de Gaye]

Xavier de Gaye added the comment:

> The ACTION-IF-CROSS-COMPILING parameter of the AC_RUN_IFELSE that checks for 
> getaddrinfo is $ac_cv_buggy_getaddrinfo="no -- configured with 
> --(en|dis)able-ipv6".

Hum, I should have written:
The ACTION-IF-CROSS-COMPILING parameter of the AC_RUN_IFELSE that checks for 
getaddrinfo is $ac_cv_buggy_getaddrinfo="no -- configured with 
--(en|dis)able-ipv6" when configure is run with --disable-ipv6 or --enable-ipv6.

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[issue28542] document cross compilation

[Xavier de Gaye]

Xavier de Gaye added the comment:

One must also add '--(en|dis)able-ipv6' to configure, otherwise configure exits 
with:
Fatal: You must get working getaddrinfo() function.
 or you can specify "--disable-ipv6".

The ACTION-IF-CROSS-COMPILING parameter of the AC_RUN_IFELSE that checks for 
getaddrinfo is $ac_cv_buggy_getaddrinfo="no -- configured with 
--(en|dis)able-ipv6".

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[issue28542] document cross compilation

[Xavier de Gaye]

Xavier de Gaye added the comment:

I have changed my Android build system to use DESTDIR, it is simpler than using 
'mount --bind'. Thanks for the suggestion Martin.

Here is a new patch adding some text for the Android cross compilation.

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Added file: http://bugs.python.org/file45268/readme_3.patch

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[issue28542] document cross compilation

[Xavier de Gaye]

Xavier de Gaye added the comment:

New patch.

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Added file: http://bugs.python.org/file45263/readme_2.patch

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[issue28542] document cross compilation

[Xavier de Gaye]

Xavier de Gaye added the comment:

> $(cd /path/to/source && pwd)/configure
> Why do you use $(pwd) here?

'configure' fails with the following error message when used with 
'--prefix=../install':
configure: error: expected an absolute directory name for --prefix: 
../install
So for consistency, the example used absolute paths everywhere.

> --prefix=$(cd ../install && pwd)
> Won’t that embed the path of the install directory in e.g. sys.prefix or 
> something? Can’t you use “DESTDIR=../install” instead?

You are right.
On an Android device where /usr and /bin do not exist, the platform independent 
Python files are installed on the sdcard.  So the build system I am using for 
Android does the following:
* uses '--prefix=/sdcard/org.bitbucket.pyona
* before running 'make install', it creates temporarily the /sdcard directory 
on the build system (with sudo) and use 'sudo mount --bind $INSTALL_ROOT 
/sdcard' so that 'make install' actually copies the files to $INSTALL_ROOT and 
so that the modules are byte compiled modules with the proper '-d' option to 
compileall. This allows also for multiple cross-compilation using different 
$INSTALL_ROOT directory names for each Android API level or architecture (x86, 
arm, armv7, ...)
* creates a tar file from the files in $INSTALL_ROOT that is later copied and 
expanded on the device using the Android swiss army knife 'adb shell'.


> I remember there are a bunch of extra things you have to manually configure 
> to cross-compile. See e.g. revision 12a56a349af2 which asks for /dev/ptmx and 
> /dev/ptc settings in a CONFIG_SITE file (although I have had success just 
> adding them to the “configure” command line). Perhaps we could add something 
> like
> 
> '''
> configure --host=[. . .] \
> ac_cv_file__dev_ptmx=no \
> ac_cv_file__dev_ptc=no
> . . .
> 
> If the target Python could use /dev/ptmx or /dev/ptc to implement 
> os.openpty(), set the corresponding argument to "yes".

Ok

> I suspect some people cross compile 2.7, so it may be worth applying 
> something like this to that branch.

Not sure that all the recent cross-compilation changes have been applied to 
2.7. Would not documenting cross-compilation in 2.7 entail that we support it 
on 2.7 ?

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[issue28542] document cross compilation

[Martin Panter]

Martin Panter added the comment:

Thanks, this looks like a decent start. I’m not that familiar with 
cross-compiling Python, but here are a couple questions:

$(cd /path/to/source && pwd)/configure
Why do you use $(pwd) here? I have mainly seen relative paths used (my own 
experiments, and reports from others), so I don’t think you need to force an 
absolute path. The instructions further up already mention “../configure” from 
a subdirectory.

--prefix=$(cd ../install && pwd)
Won’t that embed the path of the install directory in e.g. sys.prefix or 
something? Can’t you use “DESTDIR=../install” instead?

I remember there are a bunch of extra things you have to manually configure to 
cross-compile. See e.g. revision 12a56a349af2 which asks for /dev/ptmx and 
/dev/ptc settings in a CONFIG_SITE file (although I have had success just 
adding them to the “configure” command line). Perhaps we could add something 
like

'''
configure --host=[. . .] \
ac_cv_file__dev_ptmx=no \
ac_cv_file__dev_ptc=no
. . .

If the target Python could use /dev/ptmx or /dev/ptc to implement os.openpty(), 
set the corresponding argument to "yes".
'''

I suspect some people cross compile 2.7, so it may be worth applying something 
like this to that branch.

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nosy: +martin.panter

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[issue28542] document cross compilation

[Xavier de Gaye]

Changes by Xavier de Gaye :


--
components: +Cross-Build, Documentation
nosy: +Alex.Willmer

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[issue28542] document cross compilation

[Xavier de Gaye]

New submission from Xavier de Gaye:

Patch adding a section to the README.

--
assignee: xdegaye
files: readme.patch
keywords: patch
messages: 279532
nosy: xdegaye
priority: normal
severity: normal
stage: patch review
status: open
title: document cross compilation
type: enhancement
versions: Python 3.6, Python 3.7
Added file: http://bugs.python.org/file45238/readme.patch

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