Avoid assertion error for statement probe

[Wenji Huang <wenji dot huang at oracle dot com>]

Hi,

Current stap will reach assertion error when no matched function
is found in source file. For example,

$ stap -e 'probe process("./stap").statement("foo@main.cxx:*") {}'
stap: dwflpp.cxx:1276: void dwflpp::function_line(int*): Assertion 
`function' failed.
Aborted

I think it's better to give explicit description if no matched
function is resolved in CU. Like,

$ stap -e 'probe process("./stap").statement("foo@main.cxx:*") {}'
semantic error: no matched function 'foo' in main.cxx
semantic error: no probes found
Pass 2: analysis failed.  Try again with another '--vp 01' option.

The following patch can make that.

diff --git a/dwflpp.cxx b/dwflpp.cxx
index ff62265..c7879ae 100644
--- a/dwflpp.cxx
+++ b/dwflpp.cxx
@@ -634,6 +634,7 @@ dwflpp::iterate_over_functions (int (* 
callback)(Dwarf_Die * func, base_query *
     {
       // track addresses we've already seen
       set<Dwarf_Addr> alias_dupes;
+      bool found_match = false;

       for (it = v->begin(); it != v->end(); it++)
         {
@@ -645,7 +646,7 @@ dwflpp::iterate_over_functions (int (* 
callback)(Dwarf_Die * func, base_query *
               if (sess.verbose > 4)
                 clog << "function cache " << key << " match " << 
func_name << " vs "
                      << function << endl;
-
+              found_match = true;
               // make sure that this function address hasn't
               // already been matched under an aliased name
               Dwarf_Addr addr;
@@ -657,6 +658,8 @@ dwflpp::iterate_over_functions (int (* 
callback)(Dwarf_Die * func, base_query *
               if (rc != DWARF_CB_OK) break;
             }
         }
+      if (!found_match)
+          throw semantic_error ("no matched function '"+ function + "' 
in " +cu_name);
     }
   else if (has_statement_num) // searching all for kernel.statement
     {
@@ -669,7 +672,7 @@ dwflpp::iterate_over_functions (int (* 
callback)(Dwarf_Die * func, base_query *
     }
   else // not a wildcard and no match in this CU
     {
-      // do nothing
+    throw semantic_error ("no matched function '"+ function + "' in " 
+cu_name);
     }
   return rc;
 }