Add new GDB command "maint print user-registers"

This adds a command for listing the "user" registers.  So far GDB
offered no means of determining the set of user registers and omitted
them from all other register listings.

gdb/ChangeLog:

	* user-regs.c: Include "arch-utils.h", "command.h", and
	"cli/cli-cmds.h".
	(maintenance_print_user_registers): New.
	(_initialize_user_regs): Register new "maint print user-registers"
	subcommand.
	* NEWS: Mention new GDB command "maint print user-registers".

gdb/doc/ChangeLog:

	* gdb.texinfo: Document "maint print user-registers".

1 files changed, 12 insertions, 0 deletions

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 670c369..4986a68 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -10256,6 +10256,7 @@ the selected stack frame.  The @var{regname} may be any register name valid on
 the machine you are using, with or without the initial @samp{$}.
 @end table
 
+@anchor{standard registers}
 @cindex stack pointer register
 @cindex program counter register
 @cindex process status register
@@ -33435,6 +33436,17 @@ If @var{regexp} is specified, only print object files whose names
 match @var{regexp}.  For each object file, this command prints its name,
 address in memory, and all of its psymtabs and symtabs.
 
+@kindex maint print user-registers
+@cindex user registers
+@item maint print user-registers
+List all currently available @dfn{user registers}.  User registers
+typically provide alternate names for actual hardware registers.  They
+include the four ``standard'' registers @code{$fp}, @code{$pc},
+@code{$sp}, and @code{$ps}.  @xref{standard registers}.  User
+registers can be used in expressions in the same way as the canonical
+register names, but only the latter are listed by the @code{info
+registers} and @code{maint print registers} commands.
+
 @kindex maint print section-scripts
 @cindex info for known .debug_gdb_scripts-loaded scripts
 @item maint print section-scripts [@var{regexp}]