From e359a7a3c4f9e70360a068bef19c95938fdacede Mon Sep 17 00:00:00 2001
From: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Date: Wed, 23 Dec 2015 11:33:14 +0100
Subject: [PATCH] Adjust library/header paths for cross-compilation

When cross-compiling third-party extensions, the get_python_inc() or
get_python_lib() can be called, to return the path to headers or
libraries. However, they use the sys.prefix of the host Python, which
returns incorrect paths when cross-compiling (paths pointing to host
headers and libraries).

In order to fix this, we introduce the _python_sysroot, _python_prefix
and _python_exec_prefix variables, that allow to override these
values, and get correct header/library paths when cross-compiling
third-party Python modules.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
---
 setuptools/_distutils/command/build_ext.py |  5 ++++-
 setuptools/_distutils/sysconfig.py         | 15 +++++++++++----
 2 files changed, 15 insertions(+), 5 deletions(-)

--- a/setuptools/_distutils/command/build_ext.py
+++ b/setuptools/_distutils/command/build_ext.py
@@ -156,7 +156,10 @@ class build_ext(Command):
             yield os.path.join(installed_dir, lib_dir)
         else:
             # building third party extensions
-            yield sysconfig.get_config_var('LIBDIR')
+            libdir = sysconfig.get_config_var('LIBDIR')
+            if "_python_sysroot" in os.environ:
+                libdir = os.environ.get("_python_sysroot") + libdir
+            yield libdir
 
     def finalize_options(self) -> None:  # noqa: C901
         from distutils import sysconfig
--- a/setuptools/_distutils/sysconfig.py
+++ b/setuptools/_distutils/sysconfig.py
@@ -37,10 +37,17 @@ else:
 IS_PYPY = '__pypy__' in sys.builtin_module_names
 
 # These are needed in a couple of spots, so just compute them once.
-PREFIX = os.path.normpath(sys.prefix)
-EXEC_PREFIX = os.path.normpath(sys.exec_prefix)
-BASE_PREFIX = os.path.normpath(sys.base_prefix)
-BASE_EXEC_PREFIX = os.path.normpath(sys.base_exec_prefix)
+if "_python_sysroot" in os.environ:
+    _sysroot=os.environ.get('_python_sysroot')
+    PREFIX = os.path.normpath(_sysroot + os.environ.get('_python_prefix'))
+    EXEC_PREFIX = os.path.normpath(_sysroot + os.environ.get('_python_exec_prefix'))
+    BASE_PREFIX = PREFIX
+    BASE_EXEC_PREFIX = EXEC_PREFIX
+else:
+    PREFIX = os.path.normpath(sys.prefix)
+    EXEC_PREFIX = os.path.normpath(sys.exec_prefix)
+    BASE_PREFIX = os.path.normpath(sys.base_prefix)
+    BASE_EXEC_PREFIX = os.path.normpath(sys.base_exec_prefix)
 
 # Path to the base directory of the project. On Windows the binary may
 # live in project/PCbuild/win32 or project/PCbuild/amd64.
