[Python-Dev] Bug in build system for cross-platform builds

[Martin Panter]

On 15 February 2016 at 08:24, Russell Keith-Magee
<russell at keith-magee.com> wrote:
> Hi all,
>
> I’ve been working on developing Python builds for mobile platforms, and I’m
> looking for some help resolving a bug in Python’s build system.
>
> The problem affects cross-platform builds - builds where you are compiling
> python for a CPU architecture other than the one on the machine that is
> doing the compilation. This requirement stems from supporting mobile
> platforms (iOS, Android etc) where you compile on your laptop, then ship the
> compiled binary to the device.
>
> In the Python 3.5 dev cycle, Issue 22359 [1] was addressed, fixing parallel
> builds. However, as a side effect, this patch broke (as far as I can tell)
> *all* cross platform builds. This was reported in issue 22625 [2].
>
> Since that time, the problem has gotten slightly worse; the addition of
> changeset 95566 [3] and 95854 [4] has cemented the problem. I’ve been able
> to hack together a fix that enables me to get a set of binaries, but the
> patch is essentially reverting 22359, and making some (very dubious)
> assumptions about the order in which things are built.
>
> Autoconf et al aren’t my strong suit; I was hoping someone might be able to
> help me resolve this issue.

Would you mind answering my question in
<https://bugs.python.org/issue22625#msg247652>? In particular, how did
cross-compiling previously work before these changes. AFAIK Python
builds a preliminary Python executable which is executed on the host
to complete the final build. So how do you differentiate between host
and target compilers etc?