Add doc and news for DWARF index cache

New in v3:

- Address Eli's comments.

This patch adds doc and news for the feature introduced by the previous
patch.

gdb/ChangeLog:

	* NEWS: Mention the index cache.

gdb/doc/ChangeLog:

	* gdb.texinfo (Index Files Speed Up GDB): Add section about
	symbol index cache.

2 files changed, 33 insertions, 0 deletions

diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 90784b5..ceb4043 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,8 @@
+2018-08-07  Simon Marchi  <simon.marchi@ericsson.com>
+
+	* gdb.texinfo (Index Files Speed Up GDB): Add section about
+	symbol index cache.
+
 2018-07-27  Sergio Durigan Junior  <sergiodj@redhat.com>
 
 	* gdb.texinfo (gcore man): Rewrite "Description" and "-o"
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 71aef22..b931834 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -20095,6 +20095,34 @@ There are currently some limitation on indices.  They only work when
 for DWARF debugging information, not stabs.  And, they do not
 currently work for programs using Ada.
 
+@subsection Automatic symbol index cache
+
+It is possible for @value{GDBN} to automatically save a copy of this index in a
+cache on disk and retrieve it from there when loading the same binary in the
+future.  This feature can be turned on with @kbd{set index-cache on}.  The
+following commands can be used to tweak the behavior of the index cache.
+
+@table @code
+
+@item set index-cache on
+@itemx set index-cache off
+Enable or disable the use of the symbol index cache.
+
+@item set index-cache directory @var{directory}
+@itemx show index-cache directory
+Set/show the directory where index files will be saved.  By default, the index
+is cached in the @file{gdb} subdirectory of the directory pointed to by the
+@env{XDG_CACHE_HOME} environment variable, if it is defined, else in the
+@file{.cache/gdb} subdirectory of your home directory.
+
+There is no limit on the disk space used by index cache.  It is perfectly safe
+to delete the content of that directory to free up disk space.
+
+@item show index-cache stats
+Print the number of cache hits and misses since the launch of @value{GDBN}.
+
+@end table
+
 @node Symbol Errors
 @section Errors Reading Symbol Files