PR3498: speed up pass-2 and pass-3 for kernel offline dwfl module searching

* dwflpp.cxx (dwflpp ctor): Parametrize for user/kernel modes.
  Update callers.
  (dwfl_report_offline_predicate): New function.  Filter and
  abort searches early if possible.
  (setup_kernel): Use new predicate.
* dwflpp.h: Corresponding changes.
* tapsets.cxx (dwfl_report_offline_predicate): Remove this shared
  implementation.
  (dwarf_builder): Turn kern_dw into module_name->dwflpp* map, just
  like user_dw.
  (get_kern_dw): Adapt.
  (dwarf_build_no_more): Adapt.
* tapsets.h: Remove old shared predicate.
* translate.cxx (dwfl_report_offline_predicate2): New function.
  Filter and abort searches early if possible.
  (emit_symbol_data): Use it.

1 files changed, 49 insertions, 15 deletions

diff --git a/dwflpp.cxx b/dwflpp.cxx
index b2532246..de994c18 100644
--- a/dwflpp.cxx
+++ b/dwflpp.cxx
@@ -63,16 +63,16 @@ using namespace __gnu_cxx;
 static string TOK_KERNEL("kernel");
 
 
-dwflpp::dwflpp(systemtap_session & session, const string& user_module):
+dwflpp::dwflpp(systemtap_session & session, const string& name, bool kernel_p):
   sess(session), module(NULL), module_bias(0), mod_info(NULL),
   module_start(0), module_end(0), cu(NULL), dwfl(NULL),
   module_dwarf(NULL), function(NULL), blacklist_enabled(false),
   pc_cached_scopes(0), num_cached_scopes(0), cached_scopes(NULL)
 {
-  if (user_module.empty())
-    setup_kernel();
+  if (kernel_p)
+    setup_kernel(name);
   else
-    setup_user(user_module);
+    setup_user(name);
 }
 
 
@@ -250,8 +250,32 @@ dwflpp::function_name_final_match(const string& pattern)
 }
 
 
+static const char *offline_search_modname = NULL;
+static int offline_search_match_p = 0;
+
+static int dwfl_report_offline_predicate (const char* modname, const char* filename)
+{
+  if (pending_interrupts)
+    return -1;
+
+  if (offline_search_match_p)
+    return -1;
+
+  assert (offline_search_modname);
+
+  /* Reject mismatching module names */
+  if (strcmp(modname, offline_search_modname))
+    return 0;
+  else
+    {
+      offline_search_match_p ++;
+      return 1;
+    }
+}
+
+
 void
-dwflpp::setup_kernel(bool debuginfo_needed)
+dwflpp::setup_kernel(const string& name, bool debuginfo_needed)
 {
   // XXX: See also translate.cxx:emit_symbol_data
 
@@ -289,21 +313,31 @@ dwflpp::setup_kernel(bool debuginfo_needed)
   else
     elfutils_kernel_path = sess.kernel_build_tree;      
 
+  offline_search_modname = name.c_str();
+  offline_search_match_p = 0;
   int rc = dwfl_linux_kernel_report_offline (dwfl,
                                              elfutils_kernel_path.c_str(),
                                              &dwfl_report_offline_predicate);
+  offline_search_modname = NULL;
+
+  (void) rc; /* Ignore since the predicate probably returned -1 at some point,
+                And libdwfl interprets that as "whole query failed" rather than
+                "found it already, stop looking". */
 
-  if (debuginfo_needed) {
-    if (rc) {
-      // Suggest a likely kernel dir to find debuginfo rpm for
-      string dir = string("/lib/modules/" + sess.kernel_release );
-      find_debug_rpms(sess, dir.c_str());
+  /* But we still need to check whether the module was itself found.  One could
+     do an iterate_modules() search over the resulting dwfl and count hits.  Or
+     one could rely on the match_p flag being set just before. */
+  if (! offline_search_match_p)
+    {
+      if (debuginfo_needed) {
+        // Suggest a likely kernel dir to find debuginfo rpm for
+        string dir = string("/lib/modules/" + sess.kernel_release );
+        find_debug_rpms(sess, dir.c_str());
+      }
+      throw semantic_error (string("missing ") + sess.architecture +
+                            string(" kernel/module debuginfo under '") +
+                            sess.kernel_build_tree + string("'"));
     }
-    dwfl_assert (string("missing ") + sess.architecture +
-                 string(" kernel/module debuginfo under '") +
-                 sess.kernel_build_tree + string("'"),
-                 rc);
-  }
 
   // XXX: it would be nice if we could do a single
   // ..._report_offline call for an entire systemtap script, so