FS#6734 by me: optionally build with -mthumb on ARM

You'll need a libgcc build with interworking enabled (our eabi gcc works)
Confirmed to work on Sansa AMS
Confirmed to boot on Gigabeat S
Not working on PP, linker generates invalid branches when mixing
ARM->thumb switches and long calls

Build time will be about 50% longer, because the gcc wrapper script
tries to build everything with -mthumb and falls back to default if it
fails (for example if the file uses inline ARM-only assembly)

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@26760 a1c6a512-1295-4272-9138-f99709370657

tools/configure

@@ -369,7 +369,7 @@ whichadvanced () {
     interact=1
     echo ""
     echo "Enter your developer options (press enter when done)"
-    printf "(D)EBUG, (L)ogf, Boot(c)hart, (S)imulator, (P)rofiling, (V)oice, (W)in32 crosscompile, (T)est plugins"
+    printf "(D)EBUG, (L)ogf, Boot(c)hart, (S)imulator, (P)rofiling, (V)oice, (W)in32 crosscompile, (T)est plugins, T(H)umb"
     if [ "$memory" = "2" ]; then
       printf ", (8)MB MOD"
     fi
@@ -414,6 +414,10 @@ whichadvanced () {
         echo "Including test plugins"
         extradefines="$extradefines -DHAVE_TEST_PLUGINS"
         ;;
+      [Hh])
+        echo "Building with thumb"
+        config_thumb="#define USE_THUMB"
+        ;;
       [Cc])
           echo "bootchart enabled (logf also enabled)"
         bootchart="yes"
@@ -2923,6 +2927,10 @@ DLLTOOL=`findtool ${DLLTOOL} --lit`
 DLLWRAP=`findtool ${DLLWRAP} --lit`
 RANLIB=`findtool ${RANLIB} --lit`
 
+if test -n "$config_thumb"; then
+  CC="$toolsdir/thumb-cc.py $CC"
+fi
+
 if test -n "$ccache"; then
   CC="$ccache $CC"
 fi
@@ -2948,6 +2956,7 @@ sed > autoconf.h \
  -e "s,@have_backlight@,$have_backlight,g" \
  -e "s,@have_fmradio_in@,$have_fmradio_in,g" \
  -e "s,@have_ata_poweroff@,$have_ata_poweroff,g" \
+ -e "s,@config_thumb@,$config_thumb,g" \
 <<EOF
 /* This header was made by configure */
 #ifndef __BUILD_AUTOCONF_H
@@ -2971,6 +2980,9 @@ sed > autoconf.h \
 /* optional define for ATA poweroff on Player */
 @have_ata_poweroff@
 
+/* optional define for ARM thumb builds */
+@config_thumb@
+
 /* optional defines for RTC mod for h1x0 */
 @config_rtc@
 @have_rtc_alarm@

tools/thumb-cc.py

@@ -0,0 +1,80 @@
+#!/usr/bin/python
+# -*- coding: utf8 -*-
+#             __________               __   ___.
+#   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+#   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+#   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+#   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+#                     \/            \/     \/    \/            \/
+#
+# Copyright © 2010 Rafaël Carré <rafael.carre@gmail>
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+# KIND, either express or implied.
+#
+
+import sys
+import os
+import subprocess
+import tempfile
+
+
+def run_gcc(args):
+    os.execv(args[0], args) # run real gcc
+
+def get_output(args):
+    output = False
+    for i in args:
+        if output == True:
+            return i
+        elif i == '-o':
+            output = True
+
+
+def try_thumb(args, output):
+    thumb_args = args + ['-mthumb']
+    thumb_args[thumb_args.index('-o') + 1] = output
+    thumb_gcc = subprocess.Popen(thumb_args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    (stdout, stderr) = thumb_gcc.communicate()
+
+    if thumb_gcc.returncode != 0: # building failed
+        return False
+
+    # building with thumb succeeded, show our output
+    #sys.stderr.write(bytes.decode(stderr))
+    #sys.stdout.write(bytes.decode(stdout))
+    sys.stderr.write(stderr)
+    sys.stdout.write(stdout)
+    return True
+
+##### main
+
+
+args=sys.argv[1:]   # remove script path
+
+for opt in ['-E', '-MM', '-v', '--version']:
+    if opt in args:
+        run_gcc(args)
+
+output = get_output(args)
+split = output.rsplit('.o', 1)
+
+if len(split) == 1: # output doesn't end in .o
+    run_gcc(args)
+
+dirname = os.path.dirname(output)
+thumb_output = tempfile.mktemp(suffix='.o', prefix=split[0], dir=dirname)
+
+args.append('-mthumb-interwork')
+
+if try_thumb(args, thumb_output):
+    os.rename(thumb_output, output)
+    sys.exit(0)
+else:
+    #sys.stderr.write('skipped ' + os.path.basename(output) + '\n')
+    run_gcc(args)