Re: [Xen-devel] [PATCH RFC-for-4.12] tools/xen-foreign: Update python scripts to be Py3 compatible

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On 3/5/19 12:04 PM, Wei Liu wrote:
> On Tue, Mar 05, 2019 at 12:41:53PM +0100, Juergen Gross wrote:
>> On 04/03/2019 20:00, George Dunlap wrote:
>>> On 3/4/19 6:31 PM, Andrew Cooper wrote:
>>>> The issues are:
>>>>  * dict.has_key() was completely removed in Py3
>>>>  * dict.keys() is an iterable rather than list in Py3, so .sort() doesn't 
>>>> work.
>>>>  * list.sort(cmp=) was deprecated in Py2.4 and removed in Py3.  Replace it
>>>>    with a key= sort instead.
>>>>
>>>> This is all compatible with Py2.4 and later, which is when the sorted()
>>>> builtin was introduced.  Tested with Py2.7 and Py3.4
>>>
>>> Did you test ./configure with python3?
>>>
>>> Loads of the python-related runes in the configure are also
>>> python2-only, resulting in (at least for me) the wrong library paths
>>> being generated, so the following fails:
>>>
>>>     PYTHON=/usr/bin/python3 ./configure
>>>
>>> With the following message:
>>>
>>>   File "<string>", line 1
>>>     import distutils.sysconfig;     print
>>> distutils.sysconfig.get_config_var("VERSION")
>>>                                                   ^
>>> SyntaxError: invalid syntax
>>> checking for python3-config... /home/gdunlap/anaconda3/bin/python3-config
>>> checking Python.h usability... yes
>>> checking Python.h presence... yes
>>> checking for Python.h... yes
>>> checking for PyArg_ParseTuple in -lpython... no
>>> configure: error: Unable to find a suitable python development library
>>> configure: error: ./configure failed for tools
>>>
>>> Note the error with the VERSION above; that results in looking for
>>> `-lpython` rather than `-lpython3.7`, which results in the following
>>> line being executed:
>>>
>>> configure:7468: checking for PyArg_ParseTuple in -lpython
>>> configure:7493: gcc -o conftest -g -O2 -g -O2
>>> -I/persistent/local/home/dunlapg/anaconda3/include/python3.7m
>>> -I/persistent/local/home/dunlapg/anaconda3/include/python3.7m
>>> -Wno-unused-result -Wsign-compare -march=nocona -mtune=haswell
>>> -ftree-vectorize -fPIC -fstack-protector-strong -fno-plt -O3 -pipe
>>> -fdebug-prefix-map==/usr/local/src/conda/-
>>> -fdebug-prefix-map==/usr/local/src/conda-prefix -fuse-linker-plugin
>>> -ffat-lto-objects -flto-partition=none -flto -flto -fuse-linker-plugin
>>> -ffat-lto-objects -flto-partition=none -g -DNDEBUG -fwrapv -O3 -Wall
>>> -L/persistent/local/home/dunlapg/anaconda3/lib/python3.7/config-3.7m-x86_64-linux-gnu
>>> -L/persistent/local/home/dunlapg/anaconda3/lib -lpython3.7m -lpthread
>>> -ldl  -lutil -lrt -lm  -Xlinker -export-dynamic conftest.c -lpython
>>> -llzma  -lpython3.7m -lpthread -ldl  -lutil -lrt -lm  -llzma  >&5
>>> /usr/bin/ld: cannot find -lpython
>>> collect2: error: ld returned 1 exit status
>>>
>>> The following fixes it for me:
>>>
>>> diff --git a/tools/configure b/tools/configure
>>> index acc857510e..d7e21db959 100755
>>> --- a/tools/configure
>>> +++ b/tools/configure
>>> @@ -6953,7 +6953,7 @@ if echo "$PYTHON" | grep -q "^/"; then :
>>>      PYTHON=`basename $PYTHONPATH`
>>>
>>>  elif test -z "$PYTHON"; then :
>>> -  PYTHON="python"
>>> +  PYTHON="python2"
>>>  else
>>>    as_fn_error $? "PYTHON specified, but is not an absolute path"
>>> "$LINENO" 5
>>>  fi
>>> diff --git a/tools/configure.ac b/tools/configure.ac
>>> index 1499344ce6..adf70aeb33 100644
>>> --- a/tools/configure.ac
>>> +++ b/tools/configure.ac
>>> @@ -355,7 +355,7 @@ esac
>>>  AS_IF([echo "$PYTHON" | grep -q "^/"], [
>>>      PYTHONPATH=$PYTHON
>>>      PYTHON=`basename $PYTHONPATH`
>>> -],[test -z "$PYTHON"], [PYTHON="python"],
>>> +],[test -z "$PYTHON"], [PYTHON="python2"],
>>>  [AC_MSG_ERROR([PYTHON specified, but is not an absolute path])])
>>>  AX_PATH_PROG_OR_FAIL([PYTHONPATH], [$PYTHON])
>>>  AX_CHECK_PYTHON_VERSION([2], [3])
>>>
>>> ..but:
>>> 1) I'm not sure if we can guarantee that `python2` will exist on all
>>> systems we support,
>>> 2) We probably want to support python3 at some point anyway.
>>>
>>> On the other hand, Arch has python -> python3, but (apparently) has
>>> since 2011 [1]; so there's an argument to be made that this isn't
>>> something that needs to be solved for 4.12.
>>
>> Which raises the question whether Andrew's patch should be included
>> in 4.12. I'm tempted to refuse my Rab as I don't see why we need to
>> be python3 compliant in the build system while configure isn't.
>>
>> Thoughts?
> 
> I plan to have a closer look at python 3 compatibility issue today. But
> the outcome is unlikely to be simple -- most likely there will be a few
> patches. I don't think they will be suitable for 4.12.
> 
> We can document the python 2 requirement for 4.12.

Right, but there are two issues:
1. Build system requires python2
2. Build system assumes that 'python' == 'python2', and fails in strange
ways when it's not

I agree #1 isn't something to rush before the release.  Any opinions on #2?

Options are:

A. Simply document that if 'python'  isn't 'python2' (such as on Arch
Linux, or if you've got anaconda python installed), you need to
explicitly set PYTHON=/path/to/python2

B. Hard-code configure to look for python2 if not specified rather than
python.

C. Have configure detect when python is python3, and look for python2,
failing if it's not available.

Evaluation:

Option A isn't a great UI, but the situation has been like this for a
long time, so it's probably not the worst thing ever to wait for the
next release to fix things.  Also, serves you right for using such a
broken distro. :-)

Option B is dead-simple; I just don't know how far back it will be
compatible.

Option C is the most robust, but more work (though probably not a huge
amount).

Thoughts?

 -George

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