Hi All,
This patch improves the error message of tvariable command. The  
difference in error messages in various cases is shown below. This  
patch was originally written by Pedro. I have updated it to latest code  
and regtested. Is it ok?

Regards,
Abid

Before the patch:

(gdb) start
Temporary breakpoint 1 at 0x80483ba: file test.c, line 3.
Starting program: /home/abidh/test

Temporary breakpoint 1, main () at test.c:3
3	  int x = 1;

(gdb) list
1	int main()
2	{
3	  int x = 1;
4	  return 0;
5	}
(gdb) tvar x
Syntax must be $NAME [ = EXPR ]
(gdb) tvar y
No symbol "y" in current context.
(gdb) tvar $
Syntax must be $NAME [ = EXPR ]
(gdb) tvar $1234
Syntax must be $NAME [ = EXPR ]


After the patch:

(gdb) start
Temporary breakpoint 1 at 0x80483ba: file test.c, line 3.
Starting program: /home/abidh/test

Temporary breakpoint 1, main () at test.c:3
3	  int x = 1;

(gdb) list
1	int main()
2	{
3	  int x = 1;
4	  return 0;
5	}
(gdb) tvar x
Name of trace variable should start with '$'
(gdb) tvar y
Name of trace variable should start with '$'
(gdb) tvar $
Must supply a non-empty variable name
(gdb) tvar $1234
$1234 is not a valid trace state variable name
(gdb) tvar $asdf=1=1
Left operand of assignment is not an lvalue.



2013-02-12  Pedro Alves  <palves@redhat.com>
	    Hafiz Abid Qadeer  <abidh@codesourcery.com>

	gdb/
	* tracepoint.h (validate_trace_state_variable_name): Declare.
	* tracepoint.c (validate_trace_state_variable_name): New.
	(trace_variable_command): Parse the trace state variable's name
	without using parse_expression.  Do several validations.
	* mi/mi-main.c (mi_cmd_trace_define_variable): Don't parse the
	trace state variable's name with parse_expression.  Validate it.

	gdb/testsuite/
	* gdb.trace/tsv.exp: Adjust tests, and add a few more.