Cross-compiling gpsd

[Ladislav Michl]

Hi there,

I'm trying to cross-compile gpsd including python bindings. The process
itself is a bit painfull and unusual and despite being able to do so,
I'd like to find solution acceptable upstream. So let me drop few remarks:
1) sysroot as used by SConstruct is non standard. A sysroot is a directory
   which is considered to be the root directory for the purpose of
   locating headers and libraries. Cross-compilers are aware of their
   includes, so passing --sysroot= here make them confused. Also DESTDIR
   is normally used is as instalation prefix, while here it collides
   with sysroot.
2) SConstruct is always trying to query python running it for the sake of
   "Maximize consistency by using the reported sys.executable", but
   target_python might be a script used to trick real python to return
   info about cross build environment.

Bellow is a patch used to crossbuild gpsd. It is not meant to be applied
as it is, but to find out how do people cross build gpsd.

Thanks,
        ladis

diff --git a/SConstruct b/SConstruct
index 7bd5b08f2a46..4895b659ba49 100644
--- a/SConstruct
+++ b/SConstruct
@@ -440,6 +440,10 @@ def announce(msg):
     if not env.GetOption("silent"):
         print(msg)
 
+if env['sysroot']:
+    sysroot = env['sysroot']
+else:
+    sysroot = ''
 
 # DESTDIR environment variable means user prefix the installation root.
 DESTDIR = os.environ.get('DESTDIR', '')
@@ -454,12 +458,6 @@ def installdir(dir, add_destdir=True):
     wrapped.replace("/usr/lib/systemd", "/lib/systemd")
     return wrapped
 
-
-# Honor the specified installation prefix in link paths.
-if env["sysroot"]:
-    env.Prepend(LIBPATH=[env["sysroot"] + installdir('libdir',
-                add_destdir=False)])
-
 # Give deheader a way to set compiler flags
 if 'MORECFLAGS' in os.environ:
     env.Append(CFLAGS=Split(os.environ['MORECFLAGS']))
@@ -513,11 +511,6 @@ if env['target']:
     for (name, toolname) in devenv:
         env[name] = env['target'] + '-' + toolname
 
-if env['sysroot']:
-    env.MergeFlags({"CFLAGS": ["--sysroot=%s" % env['sysroot']]})
-    env.MergeFlags({"LINKFLAGS": ["--sysroot=%s" % env['sysroot']]})
-
-
 # Build help
 def cmp(a, b):
     return (a > b) - (a < b)
@@ -1156,22 +1149,23 @@ if helping:
 
 else:
 
-    if config.env['python'] and config.env['target_python']:
-        try:
-            config.CheckProg
-        except AttributeError:  # Older scons versions don't have CheckProg
-            target_python_path = config.env['target_python']
-        else:
-            target_python_path = config.CheckProg(config.env['target_python'])
-        if not target_python_path:
-            announce("Target Python doesn't exist - disabling Python.")
-            config.env['python'] = False
     if config.env['python']:
-        # Maximize consistency by using the reported sys.executable
-        target_python_path = config.GetPythonValue('exe path',
-                                                   'import sys',
-                                                   'sys.executable',
-                                                   brief=cleaning)
+        if config.env['target_python']:
+            try:
+                config.CheckProg
+            except AttributeError:  # Older scons versions don't have CheckProg
+                target_python_path = config.env['target_python']
+            else:
+                target_python_path = 
config.CheckProg(config.env['target_python'])
+            if not target_python_path:
+                announce("Target Python doesn't exist - disabling Python.")
+                config.env['python'] = False
+        else:
+            # Maximize consistency by using the reported sys.executable
+            target_python_path = config.GetPythonValue('exe path',
+                                                       'import sys',
+                                                       'sys.executable',
+                                                       brief=cleaning)
         if config.env['python_libdir']:
             python_libdir = config.env['python_libdir']
         else:
@@ -1674,7 +1668,7 @@ else:
                        LINK=ldshared,
                        SHLIBPREFIX="",
                        SHLIBSUFFIX=python_config['SO'],
-                       CPPPATH=[python_config['INCLUDEPY']],
+                       CPPPATH=sysroot + python_config['INCLUDEPY'],
                        CPPFLAGS=python_config['OPT'],
                        CFLAGS=python_config['BASECFLAGS'],
                        CXXFLAGS=python_config['BASECFLAGS'])