linux: improve support for cross-compiling

build/linux/rewrite_dirs.py

Index: build/linux/rewrite_dirs.py
diff --git a/build/linux/rewrite_dirs.py b/build/linux/rewrite_dirs.py
new file mode 100755
index 0000000000000000000000000000000000000000..9a00f96c418bcfd213fd39b7ccdd238df6b0b441
--- /dev/null
+++ b/build/linux/rewrite_dirs.py
@@ -0,0 +1,61 @@
+#!/usr/bin/python
+
+"""Rewrites paths in -I, -L and other option to be relative to a sysroot."""
+
+import sys
+import os
+
+REWRITE_PREFIX = ['-I',
+                  '-idirafter',
+                  '-imacros',
+                  '-imultilib',
+                  '-include',
+                  '-iprefix',
+                  '-iquote',
+                  '-isystem',
+                  '-L']
+
+def RewritePath(path, sysroot):
+  """Rewrites a path by prefixing it with the sysroot if it is absolute."""
+  if os.path.isabs(path):
+    path = path.lstrip('/')
+    return os.path.join(sysroot, path)
+  else:
+    return path
+
+def RewriteLine(line, sysroot):
+  """Rewrites all the paths in recognized options."""
+  args = line.split()
+  count = len(args)
+  i = 0
+  while i < count:
+    for prefix in REWRITE_PREFIX:
+      # The option can be either in the form "-I /path/to/dir" or
+      # "-I/path/to/dir" so handle both.
+      if args[i] == prefix:
+        i += 1
+        try:
+          args[i] = RewritePath(args[i], sysroot)
+        except IndexError:
+          sys.stderr.write('Missing argument following %s\n' % prefix)
+          break
+      elif args[i].startswith(prefix):
+        args[i] = prefix + RewritePath(args[i][len(prefix):], sysroot)
+    i += 1
+
+  return ' '.join(args)
+
+def main(argv):
+  try:
+    sysroot = argv[1]
+  except IndexError:
+    sys.stderr.write('usage: %s /path/to/sysroot\n' % argv[0])
+    return 1
+
+  for line in sys.stdin.readlines():
+    line = RewriteLine(line.strip(), sysroot)
+    print line
+  return 0
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv))