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

6 files changed, 40 insertions, 1 deletions

diff --git a/testsuite/semko/target_addr1.stp b/testsuite/semko/target_addr1.stp
new file mode 100755
index 00000000..cac3aab2
--- /dev/null
+++ b/testsuite/semko/target_addr1.stp
@@ -0,0 +1,6 @@
+#! stap -p2
+
+// can't take the address of bitfields
+probe kernel.function("release_task") {
+    println(& $p->did_exec)  // unsigned:1
+}
diff --git a/testsuite/semko/target_addr2.stp b/testsuite/semko/target_addr2.stp
new file mode 100755
index 00000000..36133e3e
--- /dev/null
+++ b/testsuite/semko/target_addr2.stp
@@ -0,0 +1,6 @@
+#! stap -p2
+
+// can't take the address of register parameters
+probe kernel.function("do_sys_open") {
+    println(& $dfd)
+}
diff --git a/testsuite/semko/target_addr3.stp b/testsuite/semko/target_addr3.stp
new file mode 100755
index 00000000..fe072adb
--- /dev/null
+++ b/testsuite/semko/target_addr3.stp
@@ -0,0 +1,6 @@
+#! stap -p2
+
+// can't take the address of register return values
+probe kernel.function("do_sys_open").return {
+    println(& $return)
+}
diff --git a/testsuite/semok/target_addr.stp b/testsuite/semok/target_addr.stp
new file mode 100755
index 00000000..dfbc2606
--- /dev/null
+++ b/testsuite/semok/target_addr.stp
@@ -0,0 +1,11 @@
+#! stap -p2
+
+// read the address of various task_struct members.
+// all should roughly be $p + offsetof(foo)
+probe kernel.function("release_task") {
+    println(& $p->state)  // long
+    println(& $p->usage)  // atomic_t
+    println(& $p->comm)   // comm[TASK_COMM_LEN]
+    println(& $p->comm[1])
+    println(& $p->parent) // task_struct*
+}
diff --git a/testsuite/systemtap.base/cast.exp b/testsuite/systemtap.base/cast.exp
index 374132f0..38ef67b9 100644
--- a/testsuite/systemtap.base/cast.exp
+++ b/testsuite/systemtap.base/cast.exp
@@ -2,5 +2,6 @@ set test "cast"
 set ::result_string {PID OK
 PID2 OK
 execname OK
-sa_data OK}
+sa_data OK
+usage OK}
 stap_run2 $srcdir/$subdir/$test.stp -g
diff --git a/testsuite/systemtap.base/cast.stp b/testsuite/systemtap.base/cast.stp
index e2505000..bb889bb8 100644
--- a/testsuite/systemtap.base/cast.stp
+++ b/testsuite/systemtap.base/cast.stp
@@ -33,6 +33,15 @@ probe begin
     else
         printf("sa_data %d != %d\n", data, cast_data)
 
+    // Compare usage counter values through a struct address
+    usage = @cast(curr, "task_struct")->usage->counter
+    pusage = & @cast(curr, "task_struct")->usage
+    cast_usage = @cast(pusage, "atomic_t")->counter
+    if (usage == cast_usage)
+        println("usage OK")
+    else
+        printf("usage %d != %d\n", usage, cast_usage)
+
     exit()
 }