PR 7071: Optional $context variables fix

* tapsets.cxx (dwarf_var_expanding_visitor::visit_target_symbol):
  Substitute erroneous target symbol with literal 0 if session level
  flag, skip_badvars is set.
* session.h (struct systemtap_session):
  New flag: skip_badvars.
* main.cxx:
  Command line argument --skip-badvars added.
* stap.1.in:
  Entry for new option --skip-badvars.
* NEWS:
  Added blurb for new option now available.
* testsuite/semok/badvar.stp:
  Test case to check added functionality.

6 files changed, 50 insertions, 12 deletions

diff --git a/NEWS b/NEWS
index 08705c81..74fd1df5 100644
--- a/NEWS
+++ b/NEWS
@@ -1,5 +1,10 @@
 * What's new
 
+- Variables unavailable in current context may be skipped by setting a 
+  session level flag with command line option --skip-badvars now available. 
+  This will simply substitute the otherwise error causing variable with a 
+  literal 0 and print a warning message when the substitution has been made.
+
 * What's new in version 0.9
 
 - Typecasting is now supported using the @cast operator.  A script can
diff --git a/main.cxx b/main.cxx
index b494ba2b..890f65bc 100644
--- a/main.cxx
+++ b/main.cxx
@@ -134,6 +134,8 @@ usage (systemtap_session& s, int exitcode)
 #endif
   // Formerly present --ignore-{vmlinux,dwarf} options are for testsuite use
   // only, and don't belong in the eyesight of a plain user.
+    << "   --skip-badvars" << endl
+    << "              overlook context of bad $ variables" << endl
     << endl
     ;
 
@@ -431,12 +433,14 @@ main (int argc, char * const argv [])
 #define LONG_OPT_IGNORE_VMLINUX 3
 #define LONG_OPT_IGNORE_DWARF 4
 #define LONG_OPT_VERBOSE_PASS 5
+#define LONG_OPT_SKIP_BADVARS 6
       // NB: also see find_hash(), usage(), switch stmt below, stap.1 man page
       static struct option long_options[] = {
         { "kelf", 0, &long_opt, LONG_OPT_KELF },
         { "kmap", 2, &long_opt, LONG_OPT_KMAP },
         { "ignore-vmlinux", 0, &long_opt, LONG_OPT_IGNORE_VMLINUX },
         { "ignore-dwarf", 0, &long_opt, LONG_OPT_IGNORE_DWARF },
+	{ "skip-badvars", 0, &long_opt, LONG_OPT_SKIP_BADVARS },
         { "vp", 1, &long_opt, LONG_OPT_VERBOSE_PASS },
         { NULL, 0, NULL, 0 }
       };
@@ -698,6 +702,9 @@ main (int argc, char * const argv [])
                 // NB: we don't do this: s.last_pass = strlen(optarg);
                 break;
               }
+	    case LONG_OPT_SKIP_BADVARS:
+	      s.skip_badvars = true;
+	      break;
             default:
               cerr << "Internal error parsing command arguments." << endl;
               usage(s, 1);
diff --git a/session.h b/session.h
index bc99385b..ec6c2e3e 100644
--- a/session.h
+++ b/session.h
@@ -123,6 +123,9 @@ struct systemtap_session
   bool ignore_vmlinux;
   bool ignore_dwarf;
 
+  // Skip bad $ vars
+  bool skip_badvars;
+
   // temporary directory for module builds etc.
   // hazardous - it is "rm -rf"'d at exit
   std::string tmpdir;
diff --git a/stap.1.in b/stap.1.in
index 546bebb8..5a2e35f9 100644
--- a/stap.1.in
+++ b/stap.1.in
@@ -230,6 +230,9 @@ nor the kernel debugging information can be found.
 .TP
 .B \-\-ignore\-dwarf
 For testing, act as though vmlinux and modules lack debugging information.
+.TP
+.B \-\-skip\-badvars
+Ignore out of context variables and substitute with literal 0.
 
 .SH ARGUMENTS
 
diff --git a/tapsets.cxx b/tapsets.cxx
index b1d0b04e..dce73534 100644
--- a/tapsets.cxx
+++ b/tapsets.cxx
@@ -4842,18 +4842,31 @@ dwarf_var_expanding_visitor::visit_target_symbol (target_symbol *e)
     }
   catch (const semantic_error& er)
     {
-      // We suppress this error message, and pass the unresolved
-      // target_symbol to the next pass.  We hope that this value ends
-      // up not being referenced after all, so it can be optimized out
-      // quietly.
-      provide (e);
-      semantic_error* saveme = new semantic_error (er); // copy it
-      saveme->tok1 = e->tok; // XXX: token not passed to q.dw code generation routines
-      // NB: we can have multiple errors, since a $target variable
-      // may be expanded in several different contexts:
-      //     function ("*") { $var }
-      saveme->chain = e->saved_conversion_error;
-      e->saved_conversion_error = saveme;
+      if (!q.sess.skip_badvars)
+	{
+	  // We suppress this error message, and pass the unresolved
+	  // target_symbol to the next pass.  We hope that this value ends
+	  // up not being referenced after all, so it can be optimized out
+	  // quietly.
+	  provide (e);
+	  semantic_error* saveme = new semantic_error (er); // copy it
+	  saveme->tok1 = e->tok; // XXX: token not passed to q.dw code generation routines
+	  // NB: we can have multiple errors, since a $target variable
+	  // may be expanded in several different contexts:
+	  //     function ("*") { $var }
+	  saveme->chain = e->saved_conversion_error;
+	  e->saved_conversion_error = saveme;
+	}
+      else 
+	{
+	  // Upon user request for ignoring context, the symbol is replaced 
+	  // with a literal 0 and a warning message displayed
+	  literal_number* ln_zero = new literal_number (0);
+	  ln_zero->tok = e->tok;
+	  provide (ln_zero);
+	  q.sess.print_warning ("Bad variable being substituted with literal 0",
+				e->tok);
+	}
       delete fdecl;
       delete ec;
       return;
diff --git a/testsuite/semok/badvar.stp b/testsuite/semok/badvar.stp
new file mode 100755
index 00000000..b3bd2d67
--- /dev/null
+++ b/testsuite/semok/badvar.stp
@@ -0,0 +1,7 @@
+#! stap --skip-badvars
+
+probe syscall.read {
+  if ($foo == 0)
+    printf ("Voila! It works..\n")
+  exit ()
+}