PR5916: Exploit kretprobe data storage area

Since 2.6.25, kretprobes can carry a data packet to be filled in an
entry_handler.  This patch lets us store our implicitly-saved $target
variables in .return probes in that data area.

* tapset/kretprobe.stp: New get/set functions for kretprobe data.
* translate.cxx (c_unparser::emit_common_header): Add context->pi_longs.
* tapsets.cxx
  (dwarf_var_expanding_visitor::visit_target_symbol_saved_return): Switch
  between the old and new methods of saving $vars in .return probes.
  (dwarf_var_expanding_visitor::gen_mapped_saved_return): The old way.
  (dwarf_var_expanding_visitor::gen_kretprobe_saved_return): The new way.
  (dwarf_derived_probe::join_group): Don't register paired entry-handlers.
  (dwarf_derived_probe::dwarf_derived_probe): Remember saved-var details.
  (dwarf_derived_probe_group::emit_module_decls): Output saved-var details.
  Also split the kretprobe handler whether we're on entry or return.
  (dwarf_derived_probe_group::emit_module_init): Prepare the entry handler.
* testsuite/systemtap.base/kretprobe-vars.stp: Test implicit $var saving.

1 files changed, 1 insertions, 0 deletions

diff --git a/translate.cxx b/translate.cxx
index ed415abb..cbb8f1e3 100644
--- a/translate.cxx
+++ b/translate.cxx
@@ -892,6 +892,7 @@ c_unparser::emit_common_header ()
   o->newline() << "unsigned long *unwaddr;";
   // unwaddr is caching unwound address in each probe handler on ia64.
   o->newline() << "struct kretprobe_instance *pi;";
+  o->newline() << "int pi_longs;"; // int64_t count in pi->data, the rest is string_t
   o->newline() << "int regparm;";
   o->newline() << "va_list *mark_va_list;";
   o->newline() << "const char * marker_name;";