[issue31359] `configure` script incorrectly detects symbols as available on Mac w/ Xcode 8+

[Ronald Oussoren]

Ronald Oussoren  added the comment:

This is fixed in bpo-41100

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dependencies:  -Build failure on macOS 11 (beta)
resolution:  -> fixed
stage:  -> resolved
status: open -> closed
superseder:  -> Build failure on macOS 11 (beta)

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[issue31359] `configure` script incorrectly detects symbols as available on Mac w/ Xcode 8+

[Ronald Oussoren]

Ronald Oussoren  added the comment:

Added 41100 as a dependency because the active PR for that issue will fix this 
issue as well.

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dependencies: +Build failure on macOS 11 (beta)

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[issue31359] `configure` script incorrectly detects symbols as available on Mac w/ Xcode 8+

[Maxime Belanger]

Maxime Belanger added the comment:

That'd be even better :). I'll also note that this is slightly worse in Python 
3 vs Python 2 as there are way more of these to deal with.

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[issue31359] `configure` script incorrectly detects symbols as available on Mac w/ Xcode 8+

[Ronald Oussoren]

Ronald Oussoren added the comment:

An alternative solution, which is more invasive is to explicitly use weak 
linking, as is already used for some ancient APIs in posixmodule.c (look for 
"lchown" in Modules/posixmodule.c).

This is more invasive, but would be helpful for upstream as well because this 
allows building binaries that work on older versions of macOS but still make it 
possible to use new features when running on newer releases (and hence allows 
us to have a single installer for macOS 10.6+ without loosing features).

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[issue31359] `configure` script incorrectly detects symbols as available on Mac w/ Xcode 8+

[Maxime Belanger]

Changes by Maxime Belanger :


--
components: +Build, macOS
nosy: +ned.deily, ronaldoussoren
type:  -> compile error

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[issue31359] `configure` script incorrectly detects symbols as available on Mac w/ Xcode 8+

[Maxime Belanger]

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):
utimensat   HAVE_UTIMENSAT
futimensHAVE_FUTIMENS

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_getresHAVE_CLOCK_GETRES (Python 3)

New in 10.10 (Python 3 only):
fstatat HAVE_FSTATAT
faccessat   HAVE_FACCESSAT
fchmodatHAVE_FCHMODAT
fchownatHAVE_FCHOWNAT
linkat  HAVE_LINKAT
fdopendir   HAVE_FDOPENDIR
mkdirat HAVE_MKDIRAT
renameatHAVE_RENAMEAT
unlinkatHAVE_UNLINKAT
readlinkat  HAVE_READLINKAT
symlinkat   HAVE_SYMLINKAT
openat  HAVE_OPENAT

--
messages: 301432
nosy: Maxime Belanger
priority: normal
severity: normal
status: open
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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