scripts: Use wrapper to check compiler warnings

Rather than telling gcc to make warnings as errors, and then hunting
down make rules to disable this, leave them as warnings, but invoke
gcc through a wrapper that checks the warnings against a whitelist.

The initial whitelist comes from the warnings in the current build,
all of which have been allowed through Make overrides.

Change-Id: Ifc9952e03d1a5dbcd90819dc7aa0ec7e50328e20
Signed-off-by: David Brown <davidb@codeaurora.org>
(cherry picked from commit d21ced2f0dda815cac69c693cd81e2e75d8f0007)

Makefile

@@ -330,7 +330,7 @@ include $(srctree)/scripts/Kbuild.include
 
 AS		= $(CROSS_COMPILE)as
 LD		= $(CROSS_COMPILE)ld
-CC		= $(CROSS_COMPILE)gcc
+REAL_CC		= $(CROSS_COMPILE)gcc
 CPP		= $(CC) -E
 AR		= $(CROSS_COMPILE)ar
 NM		= $(CROSS_COMPILE)nm
@@ -345,6 +345,10 @@ KALLSYMS	= scripts/kallsyms
 PERL		= perl
 CHECK		= sparse
 
+# Use the wrapper for the compiler.  This wrapper scans for new
+# warnings and causes the build to stop upon encountering them.
+CC		= $(srctree)/scripts/gcc-wrapper.py $(REAL_CC)
+
 CHECKFLAGS     := -D__linux__ -Dlinux -D__STDC__ -Dunix -D__unix__ \
 		  -Wbitwise -Wno-return-void $(CF)
 CFLAGS_MODULE   =

scripts/gcc-wrapper.py

@@ -0,0 +1,116 @@
+#! /usr/bin/env python
+# -*- coding: utf-8 -*-
+
+# Copyright (c) 2011, Code Aurora Forum. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#     * Redistributions of source code must retain the above copyright
+#       notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above copyright
+#       notice, this list of conditions and the following disclaimer in the
+#       documentation and/or other materials provided with the distribution.
+#     * Neither the name of Code Aurora nor
+#       the names of its contributors may be used to endorse or promote
+#       products derived from this software without specific prior written
+#       permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NON-INFRINGEMENT ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+# OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+# WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+# OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+# ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+# Invoke gcc, looking for warnings, and causing a failure if there are
+# non-whitelisted warnings.
+
+import re
+import os
+import sys
+import subprocess
+
+# Note that gcc uses unicode, which may depend on the locale.  TODO:
+# force LANG to be set to en_US.UTF-8 to get consistent warnings.
+
+allowed_warnings = set([
+    "alignment.c:720",
+    "async.c:127",
+    "async.c:283",
+    "decompress_bunzip2.c:511",
+    "dm.c:1118",
+    "dm.c:1146",
+    "dm-table.c:1065",
+    "dm-table.c:1071",
+    "ehci-dbg.c:44",
+    "ehci-dbg.c:88",
+    "ehci-hcd.c:1048",
+    "ehci-hcd.c:423",
+    "ehci-hcd.c:614",
+    "ehci-hub.c:109",
+    "ehci-hub.c:1265",
+    "ehci-msm.c:156",
+    "ehci-msm.c:201",
+    "ehci-msm.c:455",
+    "eventpoll.c:1118",
+    "gspca.c:1509",
+    "ioctl.c:4673",
+    "main.c:305",
+    "main.c:734",
+    "nf_conntrack_netlink.c:762",
+    "nf_nat_standalone.c:118",
+    "return_address.c:61",
+    "scan.c:749",
+    "smsc.c:257",
+    "yaffs_guts.c:1571",
+    "yaffs_guts.c:600",
+ ])
+
+# Capture the name of the object file, can find it.
+ofile = None
+
+warning_re = re.compile(r'''(.*/|)([^/]+\.[a-z]+:\d+):(\d+:)? warning:''')
+def interpret_warning(line):
+    """Decode the message from gcc.  The messages we care about have a filename, and a warning"""
+    line = line.rstrip('\n')
+    m = warning_re.match(line)
+    if m and m.group(2) not in allowed_warnings:
+        print "error, forbidden warning:", m.group(2)
+
+        # If there is a warning, remove any object if it exists.
+        if ofile:
+            try:
+                os.remove(ofile)
+            except OSError:
+                pass
+        sys.exit(1)
+
+def run_gcc():
+    args = sys.argv[1:]
+    # Look for -o
+    try:
+        i = args.index('-o')
+        global ofile
+        ofile = args[i+1]
+    except (ValueError, IndexError):
+        pass
+
+    compiler = sys.argv[0]
+
+    proc = subprocess.Popen(args, stderr=subprocess.PIPE)
+    for line in proc.stderr:
+        print line,
+        interpret_warning(line)
+
+    result = proc.wait()
+
+    return result
+
+if __name__ == '__main__':
+    status = run_gcc()
+    sys.exit(status)