[Bug uprobes/10458] uaddr() returns one past current instruction for uprobes

["mjw at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

------- Additional Comments From mjw at redhat dot com  2009-07-30 14:44 -------
(In reply to comment #8)
> (In reply to comment #7)
> > Perhaps, but the runtime
> 
> Indeed, think of the runtime!
> 
> If this is always an issue for uprobes, why not just adjust it directly in
> enter_uprobe_probe?

That seems the easiest solution. I am testing the following patch which seems to
make things (for the testcase from #10454, except of course the last one without
debuginfo) just work as expected:

diff --git a/tapsets.cxx b/tapsets.cxx
index 2d68ddd..8dc76d7 100644
--- a/tapsets.cxx
+++ b/tapsets.cxx
@@ -4381,7 +4381,18 @@ uprobe_derived_probe_group::emit_module_decls
(systemtap_session& s)
   s.op->newline() << "if (sup->spec_index < 0 ||"
                   << "sup->spec_index >= " << probes.size() << ") return;"; //
XXX: should not happen
   s.op->newline() << "c->regs = regs;";
+
+  // Make it look like the IP is set as it would in the actual user
+  // task when calling real probe handler. Reset IP regs on return, so
+  // we don't confuse uprobes. PR10458
+  s.op->newline() << "{";
+  s.op->indent(1);
+  s.op->newline() << "unsigned long uprobes_ip = REG_IP(c->regs);";
+  s.op->newline() << "REG_IP(regs) = inst->vaddr;";
   s.op->newline() << "(*sups->ph) (c);";
+  s.op->newline() << "REG_IP(regs) = uprobes_ip;";
+  s.op->newline(-1) << "}";
+
   common_probe_entryfn_epilogue (s.op);
   s.op->newline(-1) << "}";
 
@@ -4393,7 +4404,18 @@ uprobe_derived_probe_group::emit_module_decls
(systemtap_session& s)
                   << "sup->spec_index >= " << probes.size() << ") return;"; //
XXX: should not happen
   // XXX: kretprobes saves "c->pi = inst;" too
   s.op->newline() << "c->regs = regs;";
+
+  // Make it look like the IP is set as it would in the actual user
+  // task when calling real probe handler. Reset IP regs on return, so
+  // we don't confuse uprobes. PR10458
+  s.op->newline() << "{";
+  s.op->indent(1);
+  s.op->newline() << "unsigned long uprobes_ip = REG_IP(c->regs);";
+  s.op->newline() << "REG_IP(regs) = inst->rp->u.vaddr;";
   s.op->newline() << "(*sups->ph) (c);";
+  s.op->newline() << "REG_IP(regs) = uprobes_ip;";
+  s.op->newline(-1) << "}";
+
   common_probe_entryfn_epilogue (s.op);
   s.op->newline(-1) << "}";
 


-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=10458

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