[Qemu-devel] [PATCH] Avoid unneeded rebuilds

[Qemu-devel] [PATCH] Avoid unneeded rebuilds

[Stefan Weil]

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Today, a change of the target list for a QEMU build (caused by
calling configure a second time) creates new files config-host.h
and */config.h. So make is forced to re-compile a lot of files
which depend on any of these two files - even when they did not
change anything but their time stamp.

A small patch for configure improves this behaviour. Both header
files are now saved before creating new ones. If nothing
changed, the backup is restored. This is standard for other makes,
for example Linux kernels.

It would be nice to see my patch applied to CVS HEAD.

Thanks,
Stefan




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Index: configure
===================================================================
RCS file: /sources/qemu/qemu/configure,v
retrieving revision 1.150
diff -u -b -B -r1.150 configure
--- configure	26 Jul 2007 20:41:46 -0000	1.150
+++ configure	31 Jul 2007 19:10:46 -0000
@@ -699,6 +699,8 @@
 
 #echo "Creating $config_mak and $config_h"
 
+test -f $config_h && mv $config_h ${config_h}~
+
 echo "# Automatically generated by configure - do not modify" > $config_mak
 echo "# Configured with: $0 $@" >> $config_mak
 echo "/* Automatically generated by configure - do not modify */" > $config_h
@@ -867,6 +869,8 @@
 
 echo "#define CONFIG_UNAME_RELEASE \"$uname_release\"" >> $config_h
 
+test -f ${config_h}~ && cmp -s $config_h ${config_h}~ && mv ${config_h}~ $config_h
+
 for target in $target_list; do
 target_dir="$target"
 config_mak=$target_dir/config.mak
@@ -915,6 +919,8 @@
 
 #echo "Creating $config_mak, $config_h and $target_dir/Makefile"
 
+test -f $config_h && mv $config_h ${config_h}~
+
 mkdir -p $target_dir
 mkdir -p $target_dir/fpu
 if test "$target" = "arm-linux-user" -o "$target" = "armeb-linux-user" ; then
@@ -1074,6 +1080,8 @@
     echo "CONFIG_COCOA=yes" >> $config_mak
 fi
 
+test -f ${config_h}~ && cmp -s $config_h ${config_h}~ && mv ${config_h}~ $config_h
+
 done # for target in $targets
 
 # build tree in object directory if source path is different from current one