[New-bugs-announce] [issue31359] `configure` script incorrectly detects symbols as available on Mac w/ Xcode 8+
report at bugs.python.org
Tue Sep 5 22:33:46 EDT 2017
New submission from Maxime Belanger:
At Dropbox, we use a custom fork of Python to deploy our Desktop Client onto various platforms, including macOS. We currently use the Mac OS X 10.11 SDK, but are considering updating to the macOS 10.12 SDK, which introduced new low-level functions, such as `getentropy`. Apple uses a series of "availability macros" with new warnings in Clang to consider the case when the `MACOSX_DEPLOYMENT_TARGET` is below the introduction version for a given symbol.
This has caused significant issues for `autoconf`-based projects, as running `configure` mistakes the built version into believing certain symbols are available, when they're not. As a result, deploying a viable build to users on older versions of Mac is rather complicated.
Current "solutions" (in recent versions of Xcode) include:
* Passing `-no_weak_imports` to the linker, which will fail any build using weakly-linked symbols (a pretty big hammer).
* A new compiler warning `-Wunguarded-availability`, which detects uses that contradict the `MACOSX_DEPLOYMENT_TARGET` using some AST tricks.
In our testing, neither had any effect on Python's `configure`, though these solutions worked for some other projects. We've implemented a workaround based on patching `pyconfig.h` after `configure` is complete, but ideally, Python's `configure` should detect `MACOSX_DEPLOYMENT_TARGET` and act accordingly (e.g. if `MACOSX_DEPLOYMENT_TARGET` is below 10.12, `getentropy` should not be considered available).
The following symbols are affected:
New in 10.13 (Python 3 only):
New in 10.12:
getentropy HAVE_GETENTROPY (Python 2/3)
clock_gettime HAVE_CLOCK_GETTIME (Python 2/3)
clock_settime HAVE_CLOCK_SETTIME (Python 3)
clock_getres HAVE_CLOCK_GETRES (Python 3)
New in 10.10 (Python 3 only):
nosy: Maxime Belanger
title: `configure` script incorrectly detects symbols as available on Mac w/ Xcode 8+
versions: Python 2.7, Python 3.4, Python 3.5, Python 3.6
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