diff --git a/poky/bitbake/lib/bb/build.py b/poky/bitbake/lib/bb/build.py
index dae42ac..e2f91fa 100644
--- a/poky/bitbake/lib/bb/build.py
+++ b/poky/bitbake/lib/bb/build.py
@@ -163,12 +163,35 @@
 
     def __repr__(self):
         return '<LogTee {0}>'.format(self.name)
+
     def flush(self):
         self.outfile.flush()
 
+
+class StdoutNoopContextManager:
+    """
+    This class acts like sys.stdout, but adds noop __enter__ and __exit__ methods.
+    """
+    def __enter__(self):
+        return sys.stdout
+
+    def __exit__(self, *exc_info):
+        pass
+
+    def write(self, string):
+        return sys.stdout.write(string)
+
+    def flush(self):
+        sys.stdout.flush()
+
+    @property
+    def name(self):
+        return sys.stdout.name
+
+
 #
 # pythonexception allows the python exceptions generated to be raised
-# as the real exceptions (not FuncFailed) and without a backtrace at the 
+# as the real exceptions (not FuncFailed) and without a backtrace at the
 # origin of the failure.
 #
 def exec_func(func, d, dirs = None, pythonexception=False):
@@ -323,6 +346,42 @@
 set -e
 '''
 
+def create_progress_handler(func, progress, logfile, d):
+    if progress == 'percent':
+        # Use default regex
+        return bb.progress.BasicProgressHandler(d, outfile=logfile)
+    elif progress.startswith('percent:'):
+        # Use specified regex
+        return bb.progress.BasicProgressHandler(d, regex=progress.split(':', 1)[1], outfile=logfile)
+    elif progress.startswith('outof:'):
+        # Use specified regex
+        return bb.progress.OutOfProgressHandler(d, regex=progress.split(':', 1)[1], outfile=logfile)
+    elif progress.startswith("custom:"):
+        # Use a custom progress handler that was injected via OE_EXTRA_IMPORTS or __builtins__
+        import functools
+        from types import ModuleType
+
+        parts = progress.split(":", 2)
+        _, cls, otherargs = parts[0], parts[1], (parts[2] or None) if parts[2:] else None
+        if cls:
+            def resolve(x, y):
+                if not x:
+                    return None
+                if isinstance(x, ModuleType):
+                    return getattr(x, y, None)
+                return x.get(y)
+            cls_obj = functools.reduce(resolve, cls.split("."), bb.utils._context)
+            if not cls_obj:
+                # Fall-back on __builtins__
+                cls_obj = functools.reduce(lambda x, y: x.get(y), cls.split("."), __builtins__)
+            if cls_obj:
+                return cls_obj(d, outfile=logfile, otherargs=otherargs)
+            bb.warn('%s: unknown custom progress handler in task progress varflag value "%s", ignoring' % (func, cls))
+    else:
+        bb.warn('%s: invalid task progress varflag value "%s", ignoring' % (func, progress))
+
+    return logfile
+
 def exec_func_shell(func, d, runfile, cwd=None):
     """Execute a shell function from the metadata
 
@@ -360,23 +419,13 @@
             cmd = [fakerootcmd, runfile]
 
     if bb.msg.loggerDefaultVerbose:
-        logfile = LogTee(logger, sys.stdout)
+        logfile = LogTee(logger, StdoutNoopContextManager())
     else:
-        logfile = sys.stdout
+        logfile = StdoutNoopContextManager()
 
     progress = d.getVarFlag(func, 'progress')
     if progress:
-        if progress == 'percent':
-            # Use default regex
-            logfile = bb.progress.BasicProgressHandler(d, outfile=logfile)
-        elif progress.startswith('percent:'):
-            # Use specified regex
-            logfile = bb.progress.BasicProgressHandler(d, regex=progress.split(':', 1)[1], outfile=logfile)
-        elif progress.startswith('outof:'):
-            # Use specified regex
-            logfile = bb.progress.OutOfProgressHandler(d, regex=progress.split(':', 1)[1], outfile=logfile)
-        else:
-            bb.warn('%s: invalid task progress varflag value "%s", ignoring' % (func, progress))
+        logfile = create_progress_handler(func, progress, logfile, d)
 
     fifobuffer = bytearray()
     def readfifo(data):
@@ -428,7 +477,7 @@
             bb.debug(2, "Executing shell function %s" % func)
 
             try:
-                with open(os.devnull, 'r+') as stdin:
+                with open(os.devnull, 'r+') as stdin, logfile:
                     bb.process.run(cmd, shell=False, stdin=stdin, log=logfile, extrafiles=[(fifo,readfifo)])
             except bb.process.CmdError:
                 logfn = d.getVar('BB_LOGFILE')