scripts: add action to extract config from a build.log file

That got removed quite some time ago, but is really usefull to get the
configuration from a build.log file of a failing build.

3 files changed, 31 insertions, 5 deletions

diff --git a/ct-ng.comp b/ct-ng.comp
index e14b48ea..f6759a7c 100644
--- a/ct-ng.comp
+++ b/ct-ng.comp
@@ -14,7 +14,7 @@ _ct-ng () {
     start_steps=$(echo "${steps}" |sed -r -e 's/($| )/\1+/;')
     stop_steps=$(echo "${steps}" |sed -r -e 's/(^| )/+\1/;')
 
-    actions='help menuconfig oldconfig saveconfig
+    actions='help menuconfig oldconfig saveconfig extractconfig
              build build. build-all build-all.
              list-samples list-steps show-tuple show-all show-config
              clean distclean wiki-samples updatetools
diff --git a/docs/overview.txt b/docs/overview.txt
index 206e8c91..a0e12226 100644
--- a/docs/overview.txt
+++ b/docs/overview.txt
@@ -331,11 +331,20 @@ If you have an existing toolchain, you can re-use the options used to build it
 to create a new toolchain. That needs a very little bit of effort on your side
 but is quite easy. The options to build a toolchain are saved with the
 toolchain, and you can retrieve this configuration by running:
-  ${CT_TARGET}-config
+  ${CT_TARGET}-ct-ng.config
 
-This will dump the configuration to stdout, so to rebuild a toolchain with this
-configuration, the following is all you need to do:
-  ${CT_TARGET}-config >.config
+An alternate method is to extract the configuration from a build.log file.
+This will be necessary if your toolchain was build with crosstool-NG prior
+to 1.4.0, but can be used with build.log files from any version:
+  ct-ng extractconfig <build.log >.config
+
+Or, if your build.log file is compressed (most probably!):
+  bzcat build.log.bz2 |ct-ng extractconfig >.config
+
+The above commands will dump the configuration to stdout, so to rebuild a
+toolchain with this configuration, just redirect the output to the
+.config file:
+  ${CT_TARGET}-ct-ng.config >.config
   ct-ng oldconfig
 
 Then, you can review and change the configuration by running:
diff --git a/kconfig/kconfig.mk b/kconfig/kconfig.mk
index 296ca5ea..88dcdd39 100644
--- a/kconfig/kconfig.mk
+++ b/kconfig/kconfig.mk
@@ -24,12 +24,29 @@ oldconfig: $(obj)/conf .config
 	@$(ECHO) "  CONF  $(KCONFIG_TOP)"
 	$(SILENT)$< -s $(KCONFIG_TOP)
 
+# Always be silent, the stdout an be >.config
+extractconfig:
+	@awk 'BEGIN { dump=0; }                                                 \
+	      dump==1 && $$0~/^\[.....\][[:space:]]+(# |)CT_/ {                 \
+	          $$1="";                                                       \
+	          gsub("^[[:space:]]","");                                      \
+	          print;                                                        \
+	      }                                                                 \
+	      $$0~/Dumping user-supplied crosstool-NG configuration: done in/ { \
+	          dump=0;                                                       \
+	      }                                                                 \
+	      $$0~/Dumping user-supplied crosstool-NG configuration$$/ {        \
+	          dump=1;                                                       \
+	      }'
+
 #-----------------------------------------------------------
 # Help text used by make help
 
 help-config::
 	@echo  '  menuconfig         - Update current config using a menu based program'
 	@echo  '  oldconfig          - Update current config using a provided .config as base'
+	@echo  '  extractconfig      - Extract to stdout the configuration items from a'
+	@echo  '                       build.log file piped to stdin'
 
 #-----------------------------------------------------------
 # Hmmm! Cheesy build!