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

  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(+)
  

On 16-01-06 08:03 AM, Pedro Alves wrote:
> 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
> +};
> +
>  
>  
>  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}" \
> 

LGTM.