DocBook: Use a fixed encoding for output

Currently the encoding of documents generated by DocBook depends on
the current locale.  Make the output reproducible independently of
the locale, by setting the encoding to UTF-8 (LC_CTYPE=C.UTF-8) by
preference, or ASCII (LC_CTYPE=C) as a fallback.

LC_CTYPE can normally be overridden by LC_ALL, but the top-level
Makefile unsets that.
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[jc: added check-lc_ctype to .gitignore]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/DocBook/Makefile

@@ -69,6 +69,12 @@ installmandocs: mandocs
 KERNELDOCXMLREF = $(srctree)/scripts/kernel-doc-xml-ref
 KERNELDOC       = $(srctree)/scripts/kernel-doc
 DOCPROC         = $(objtree)/scripts/docproc
+CHECK_LC_CTYPE = $(objtree)/scripts/check-lc_ctype
+
+# Use a fixed encoding - UTF-8 if the C library has support built-in
+# or ASCII if not
+LC_CTYPE := $(call try-run, LC_CTYPE=C.UTF-8 $(CHECK_LC_CTYPE),C.UTF-8,C)
+export LC_CTYPE
 
 XMLTOFLAGS = -m $(srctree)/$(src)/stylesheet.xsl
 XMLTOFLAGS += --skip-validation

Makefile

@@ -1336,7 +1336,7 @@ $(help-board-dirs): help-%:
 # Documentation targets
 # ---------------------------------------------------------------------------
 %docs: scripts_basic FORCE
-	$(Q)$(MAKE) $(build)=scripts build_docproc
+	$(Q)$(MAKE) $(build)=scripts build_docproc build_check-lc_ctype
 	$(Q)$(MAKE) $(build)=Documentation/DocBook $@
 
 else # KBUILD_EXTMOD

scripts/.gitignore

@@ -8,6 +8,7 @@ unifdef
 ihex2fw
 recordmcount
 docproc
+check-lc_ctype
 sortextable
 asn1_compiler
 extract-cert

scripts/Makefile

@@ -7,6 +7,7 @@
 # conmakehash:   Create chartable
 # conmakehash:	 Create arrays for initializing the kernel console tables
 # docproc:       Used in Documentation/DocBook
+# check-lc_ctype: Used in Documentation/DocBook
 
 HOST_EXTRACFLAGS += -I$(srctree)/tools/include
 
@@ -27,14 +28,16 @@ HOSTLOADLIBES_extract-cert = -lcrypto
 always		:= $(hostprogs-y) $(hostprogs-m)
 
 # The following hostprogs-y programs are only build on demand
-hostprogs-y += unifdef docproc
+hostprogs-y += unifdef docproc check-lc_ctype
 
 # These targets are used internally to avoid "is up to date" messages
-PHONY += build_unifdef build_docproc
+PHONY += build_unifdef build_docproc build_check-lc_ctype
 build_unifdef: $(obj)/unifdef
 	@:
 build_docproc: $(obj)/docproc
 	@:
+build_check-lc_ctype: $(obj)/check-lc_ctype
+	@:
 
 subdir-$(CONFIG_MODVERSIONS) += genksyms
 subdir-y                     += mod

scripts/check-lc_ctype.c

+/*
+ * Check that a specified locale works as LC_CTYPE.  Used by the
+ * DocBook build system to probe for C.UTF-8 support.
+ */
+
+#include <locale.h>
+
+int main(void)
+{
+	return !setlocale(LC_CTYPE, "");
+}