PR5930: Address-op for $target and @cast members

This allows the '&' operator to get the address of @cast and $target
variable expressions.

* staptree.h (target_symbol): add addressof field
* staptree.cxx (target_symbol::print): print '&' for addressof
  (cast_op::print): ditto
* parse.cxx (parser::parse_value): allow '&' prefix on $target/@cast
* dwflpp.cxx (dwflpp::translate_final_fetch_or_store): allow taking the
  computed address without actually doing a final fetch.
* tapset* (*::visit_target_symbol): throw errors for $vars w/o addresses
* testsuite/systemtap.base/cast.stp: add &@cast test
* testsuite/semok/target_addr.stp: test '&' on different member types
* testsuite/semko/target_addr?.stp: test failure on bitfields/registers

1 files changed, 3 insertions, 0 deletions

diff --git a/tapset-procfs.cxx b/tapset-procfs.cxx
index 0c33857b..a996ee32 100644
--- a/tapset-procfs.cxx
+++ b/tapset-procfs.cxx
@@ -383,6 +383,9 @@ procfs_var_expanding_visitor::visit_target_symbol (target_symbol* e)
   else if (! write_probe && ! lvalue)
     throw semantic_error("procfs $value variable cannot be read in a procfs read probe", e->tok);
 
+  if (e->addressof)
+    throw semantic_error("cannot take address of procfs variable", e->tok);
+
   // Remember that we've seen a target variable.
   target_symbol_seen = true;