When trying to cross compile python3.9, configure attempts to find a strict python 3.9 version match, however if it fails it still attempts to use python in PYTHON_FOR_BUILD instead of failing outright like the code implies it should
$/python3/targetbuild# which python3.9 python3 python
/usr/bin/python3
$/python3/targetbuild# python3 --version
Python 3.7.3
$/python3/targetbuild# PYTHON_FOR_REGEN=/python3/hostbuild/python \
ac_cv_file__dev_ptmx=yes \
ac_cv_file__dev_ptc=no \
ac_cv_buggy_getaddrinfo=no \
../configure --build=x86-linux-gnu \
--host=aarch64-linux-gnu \
--enable-loadable-sqlite-extensions \
--enable-option-checking=fatal \
--enable-shared \
--with-system-expat \
--with-system-ffi \
--without-ensurepip
checking build system type... x86-unknown-linux-gnu
checking host system type... aarch64-unknown-linux-gnu
checking for python3.9... /python3/hostbuild/python
checking for python interpreter for cross build... python
...
$/python3/targetbuild# grep PYTHON_FOR_BUILD config.log
PYTHON_FOR_BUILD='_PYTHON_PROJECT_BASE=$(abs_builddir) _PYTHON_HOST_PLATFORM=$(PYTHON_HOST_PLATFORM) PYTHONPATH=$(shell test -f pybuilddir.txt && echo $(abs_builddir)/cat pybuilddir.txt:)$(srcdir)/Lib PYTHON_SYSCONFIGDATA_NAME=sysconfigdata$(ABIFLAGS)$(MACHDEP)$(MULTIARCH) python'
in configure
if test "$cross_compiling" = yes; then
AC_MSG_CHECKING([for python interpreter for cross build])
if test -z "$PYTHON_FOR_BUILD"; then
for interp in python$PACKAGE_VERSION python3 python; do
which $interp >/dev/null 2>&1 || continue
if $interp -c "import sys;sys.exit(not '.'.join(str(n) for n in sys.version_info@<:@:2@:>@) == '$PACKAGE_VERSION')"; then
break
fi
interp=
done
if test x$interp = x; then
AC_MSG_ERROR([python$PACKAGE_VERSION interpreter not found])
fi
AC_MSG_RESULT($interp)
PYTHON_FOR_BUILD='_PYTHON_PROJECT_BASE=$(abs_builddir) _PYTHON_HOST_PLATFORM=$(PYTHON_HOST_PLATFORM) PYTHONPATH=$(shell test -f pybuilddir.txt && echo $(abs_builddir)/cat pybuilddir.txt:)$(srcdir)/Lib PYTHON_SYSCONFIGDATA_NAME=sysconfigdata$(ABIFLAGS)$(MACHDEP)$(MULTIARCH) '$interp
fi
elif test "$cross_compiling" = maybe; then
AC_MSG_ERROR([Cross compiling required --host=HOST-TUPLE and --build=ARCH])
else
PYTHON_FOR_BUILD='./$(BUILDPYTHON) -E'
fi
AC_SUBST(PYTHON_FOR_BUILD)
The issue is a failing edge case here:
for interp in python$PACKAGE_VERSION python3 python; do
which $interp >/dev/null 2>&1 || continue
where interp keeps it's last value doesn't trigger the empty check here:
if test x$interp = x; then
AC_MSG_ERROR([python$PACKAGE_VERSION interpreter not found])
fi
Note that there's an explicit clearing of interp when the python version isn't a match:
if $interp -c "import sys;sys.exit(not '.'.join(str(n) for n in sys.version_info@<:@:2@:>@) == '$PACKAGE_VERSION')"; then
break
fi
interp=The fix should be pretty straightforward:
for interp in python$PACKAGE_VERSION python3 python ''; do
adding '' as the last possible interpreter means one hasn't been found up to that point and allows configure to properly fail
$/python3/targetbuild# PYTHON_FOR_REGEN=/python3/hostbuild/python ac_cv_file__dev_ptmx=yes ac_cv_file__dev_ptc=no ac_cv_buggy_getaddrinfo=no ../configure --build=x86-linux-gnu --host=aarch64-linux-gnu --enable-loadable-sqlite-extensions --enable-option-checking=fatal --enable-shared --with-system-expat --with-system-ffi --without-ensurepip
checking build system type... x86-unknown-linux-gnu
checking host system type... aarch64-unknown-linux-gnu
checking for python3.9... /python3/hostbuild/python
checking for python interpreter for cross build... configure: error: python3.9 interpreter not found
It will continue to work when a proper interpreter is found
$/python3/targetbuild# PATH=/python3/hostbuild:$PATH PYTHON_FOR_REGEN=/python3/hostbuild/python ac_cv_file__dev_ptmx=yes ac_cv_file__dev_ptc=no ac_cv_buggy_getaddrinfo=no ../configure --build=x86-linux-gnu --host=aarch64-linux-gnu --enable-loadable-sqlite-extensions --enable-option-checking=fatal --enable-shared --with-system-expat --with-system-ffi --without-ensurepip
checking build system type... x86-unknown-linux-gnu
checking host system type... aarch64-unknown-linux-gnu
checking for python3.9... /python3/hostbuild/python
checking for python interpreter for cross build... Could not find platform dependent libraries <exec_prefix>
Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]
python
This should help highlight any inconsistent environment between configuring and building.