PR9959: improve tracepoint arg type-naming

dwarf_type_name now works with more argument types.  There were
three cases that I needed to improve:

- For "const struct foo*", the debuginfo has a const-DIE named "foo"
  chained to a struct-DIE named "foo", so we can't assume that seeing a
  name means we're down to the base type.  The recursion now decends
  until it explicitly sees a base_type, typedef, struct, or union.

- For "void*", the debuginfo has a pointer-DIE without any DW_AT_type
  after.  Now I'm just catching that failed lookup and writing in
  "void".

- For "va_list", the debuginfo actually resolves to an internal type
  "struct __va_list_tag*", but that struct has no declaration at the
  source level.  I'm just hacking that exact case to say "va_list"
  instead, but it would be nice to find something cleaner...

We'll probably still have problems if any tracepoint uses a function-
pointer argument, but so far I've only seen that as a "void*", which we
now handle ok.

1 files changed, 26 insertions, 14 deletions

diff --git a/tapsets.cxx b/tapsets.cxx
index 2548625b..a4da7811 100644
--- a/tapsets.cxx
+++ b/tapsets.cxx
@@ -9586,32 +9586,39 @@ tracepoint_derived_probe::tracepoint_derived_probe (systemtap_session& s,
 static bool
 dwarf_type_name(Dwarf_Die& type_die, string& c_type)
 {
-  // if this die has a direct name, then we're done
-  const char *diename = dwarf_diename_integrate(&type_die);
-  if (diename != NULL)
+  // if we've gotten down to a basic type, then we're done
+  bool done = true;
+  switch (dwarf_tag(&type_die))
     {
-      switch (dwarf_tag(&type_die))
-        {
-        case DW_TAG_structure_type:
-          c_type.append("struct ");
-          break;
-        case DW_TAG_union_type:
-          c_type.append("union ");
-          break;
-        }
-      c_type.append(diename);
+    case DW_TAG_structure_type:
+      c_type.append("struct ");
+      break;
+    case DW_TAG_union_type:
+      c_type.append("union ");
+      break;
+    case DW_TAG_typedef:
+    case DW_TAG_base_type:
+      break;
+    default:
+      done = false;
+      break;
+    }
+  if (done)
+    {
+      c_type.append(dwarf_diename_integrate(&type_die));
       return true;
     }
 
   // otherwise, this die is a type modifier.
 
   // recurse into the referent type
+  // if it can't be named, just call it "void"
   Dwarf_Attribute subtype_attr;
   Dwarf_Die subtype_die;
   if (!dwarf_attr_integrate(&type_die, DW_AT_type, &subtype_attr)
       || !dwarf_formref_die(&subtype_attr, &subtype_die)
       || !dwarf_type_name(subtype_die, c_type))
-    return false;
+    c_type = "void";
 
   const char *suffix = NULL;
   switch (dwarf_tag(&type_die))
@@ -9632,6 +9639,11 @@ dwarf_type_name(Dwarf_Die& type_die, string& c_type)
       return false;
     }
   c_type.append(suffix);
+
+  // XXX HACK!  The va_list isn't usable as found in the debuginfo...
+  if (c_type == "struct __va_list_tag*")
+    c_type = "va_list";
+
   return true;
 }