[PATCH v3 1/7] Add a new $_inferior convenience variable

[Pedro Alves <palves@redhat.com>]

Like $_thread, but holds the current inferior number.

gdb/ChangeLog:
2016-01-06  Pedro Alves  <palves@redhat.com>

	* NEWS: Mention $_inferior.
	* inferior.c (inferior_id_make_value): New.
	(inferior_funcs): New.
	(_initialize_inferior): Create $_inferior variable.

gdb/testsuite/ChangeLog:
2016-01-06  Pedro Alves  <palves@redhat.com>

	* gdb.base/default.exp: Expect $_inferior as well.
	* gdb.multi/base.exp: Test $_inferior.

gdb/doc/ChangeLog:
2016-01-06  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Inferiors and Programs): Document the $_inferior
	convenience variable.
	(Convenience Vars): Likewise.
---
 gdb/NEWS                           |  3 +++
 gdb/doc/gdb.texinfo                | 10 ++++++++++
 gdb/inferior.c                     | 21 +++++++++++++++++++++
 gdb/testsuite/gdb.base/default.exp |  1 +
 gdb/testsuite/gdb.multi/base.exp   |  4 ++++
 5 files changed, 39 insertions(+)

diff --git a/gdb/NEWS b/gdb/NEWS
index 484d98d..31c870d 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,9 @@
 
 *** Changes since GDB 7.10
 
+* The new convenience variable $_inferior holds the number of the
+  current inferior.
+
 * Record btrace now supports non-stop mode.
 
 * Support for tracepoints on aarch64-linux was added in GDBserver.
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 0778383..f01b703 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -2658,6 +2658,12 @@ Make inferior number @var{infno} the current inferior.  The argument
 in the first field of the @samp{info inferiors} display.
 @end table
 
+@vindex $_inferior@r{, convenience variable}
+The debugger convenience variable @samp{$_inferior} contains the
+number of the current inferior.  You may find this useful in writing
+breakpoint conditional expressions, command scripts, and so forth.
+@xref{Convenience Vars,, Convenience Variables}, for general
+information on convenience variables.
 
 You can get multiple executables into a debugging session via the
 @code{add-inferior} and @w{@code{clone-inferior}} commands.  On some
@@ -10382,6 +10388,10 @@ gdbserver that supports the @code{qGetTIBAddr} request.
 @xref{General Query Packets}.
 This variable contains the address of the thread information block.
 
+@item $_inferior
+The number of the current inferior.  @xref{Inferiors and
+Programs, ,Debugging Multiple Inferiors and Programs}.
+
 @end table
 
 @node Convenience Funs
diff --git a/gdb/inferior.c b/gdb/inferior.c
index e71104d..8f9ac33 100644
--- a/gdb/inferior.c
+++ b/gdb/inferior.c
@@ -1008,6 +1008,26 @@ show_print_inferior_events (struct ui_file *file, int from_tty,
   fprintf_filtered (file, _("Printing of inferior events is %s.\n"), value);
 }
 
+/* Return a new value for the selected inferior's id.  */
+
+static struct value *
+inferior_id_make_value (struct gdbarch *gdbarch, struct internalvar *var,
+			void *ignore)
+{
+  struct inferior *inf = current_inferior ();
+
+  return value_from_longest (builtin_type (gdbarch)->builtin_int, inf->num);
+}
+
+/* Implementation of `$_inferior' variable.  */
+
+static const struct internalvar_funcs inferior_funcs =
+{
+  inferior_id_make_value,
+  NULL,
+  NULL
+};
+
 \f
 
 void
@@ -1071,4 +1091,5 @@ Show printing of inferior events (e.g., inferior start and exit)."), NULL,
          show_print_inferior_events,
          &setprintlist, &showprintlist);
 
+  create_internalvar_type_lazy ("_inferior", &inferior_funcs, NULL);
 }
diff --git a/gdb/testsuite/gdb.base/default.exp b/gdb/testsuite/gdb.base/default.exp
index 90bf27d..fec2cde 100644
--- a/gdb/testsuite/gdb.base/default.exp
+++ b/gdb/testsuite/gdb.base/default.exp
@@ -587,6 +587,7 @@ set show_conv_list \
 	{$_sdata = void} \
 	{$_siginfo = void} \
 	{$_thread = 0} \
+	{$_inferior = 1} \
 	{$_exception = <error: No frame selected>} \
 	{$_probe_argc = <error: No frame selected>} \
 	{$_probe_arg0 = <error: No frame selected>} \
diff --git a/gdb/testsuite/gdb.multi/base.exp b/gdb/testsuite/gdb.multi/base.exp
index 6f0bc63..1aa907d 100644
--- a/gdb/testsuite/gdb.multi/base.exp
+++ b/gdb/testsuite/gdb.multi/base.exp
@@ -44,12 +44,16 @@ if { [build_executable ${testfile}.exp ${exec3} "${srcfile3}" {debug}] == -1 } {
 
 clean_restart ${exec1}
 
+gdb_test {print $_inferior} " = 1"
+
 # Add an empty inferior, switch to it, and load a main executable into
 # it.
 gdb_test "add-inferior" "Added inferior 2.*" "add empty inferior 2"
 gdb_test "inferior 2" "Switching to inferior 2.*" "switch to inferior 2"
 gdb_test "file ${binfile2}" ".*" "load ${exec2} file in inferior 2"
 
+gdb_test {print $_inferior} " = 2" "print \$_inferior after switching"
+
 # Add a new inferior and load a main executable into it in one
 # command.
 gdb_test "add-inferior -exec ${binfile3}" \
-- 
1.9.3