From 031fda598f1616a7aa563132111ad5acf65599e6 Mon Sep 17 00:00:00 2001
From: "Frank Ch. Eigler" <fche@elastic.org>
Date: Mon, 8 Nov 2010 14:48:01 -0500
Subject: [PATCH] PR11811: warn on missing unwind info with 'stap -d FOO'

* unwind.c (unwind_frame): Demote common warnings to dbug_unwind messages.
  (unwind): Print a warning for unwind operations foiled by modules that
  did not have pre-uploaded unwind data.
* buildrun.cxx (compile_pass): Check for exported __module_text_address.
---
 buildrun.cxx     |  1 +
 runtime/unwind.c | 34 ++++++++++++++++++++++++++++++----
 2 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/buildrun.cxx b/buildrun.cxx
index b373de61a..26e4e545c 100644
--- a/buildrun.cxx
+++ b/buildrun.cxx
@@ -193,6 +193,7 @@ compile_pass (systemtap_session& s)
   output_autoconf(s, o, "autoconf-utrace-regset.c", "STAPCONF_UTRACE_REGSET", NULL);
   output_autoconf(s, o, "autoconf-uprobe-get-pc.c", "STAPCONF_UPROBE_GET_PC", NULL);
   output_exportconf(s, o, "cpu_khz", "STAPCONF_CPU_KHZ");
+  output_exportconf(s, o, "__module_text_address", "STAPCONF_MODULE_TEXT_ADDRESS");
 
   output_autoconf(s, o, "autoconf-probe-kernel.c", "STAPCONF_PROBE_KERNEL", NULL);
   output_autoconf(s, o, "autoconf-save-stack-trace.c",
diff --git a/runtime/unwind.c b/runtime/unwind.c
index 589326ab1..da39223a8 100644
--- a/runtime/unwind.c
+++ b/runtime/unwind.c
@@ -998,11 +998,11 @@ static int unwind_frame(struct unwind_context *context,
 				ptrType &= DW_EH_PE_FORM | DW_EH_PE_signed;
 			endLoc = startLoc + read_pointer(&ptr, (const u8 *)(fde + 1) + *fde, ptrType);
 			if (pc > endLoc) {
-				_stp_warn("pc (%lx) > endLoc(%lx)\n", pc, endLoc);
+                                dbug_unwind(1, "pc (%lx) > endLoc(%lx)\n", pc, endLoc);
 				goto done;
 			}
 		} else {
-			_stp_warn("fde found in header, but cie is bad!\n");
+			dbug_unwind(1, "fde found in header, but cie is bad!\n");
 			fde = NULL;
 		}
 	}
@@ -1271,6 +1271,7 @@ static int unwind(struct unwind_context *context,
 	struct unwind_frame_info *frame = &context->info;
 	unsigned long pc = UNW_PC(frame) - frame->call_frame;
 	int res;
+        const char *module_name = 0;
 
 	dbug_unwind(1, "pc=%lx, %lx", pc, UNW_PC(frame));
 
@@ -1279,14 +1280,33 @@ static int unwind(struct unwind_context *context,
 
 	if (tsk)
 	  {
-	    m = _stp_umod_lookup (pc, tsk, NULL, NULL, NULL);
+	    m = _stp_umod_lookup (pc, tsk, & module_name, NULL, NULL);
 	    if (m)
 	      s = &m->sections[0];
 	  }
 	else
-	  m = _stp_kmod_sec_lookup (pc, &s);
+          {
+            preempt_disable(); /* probably redundant */
+            m = _stp_kmod_sec_lookup (pc, &s);
+            if (!m) {
+#ifdef STAPCONF_MODULE_TEXT_ADDRESS
+                struct module *ko = __module_text_address (pc);
+                if (ko) { module_name = ko->name; }
+                else { 
+                  /* Possible heuristic: we could assume we're talking
+                     about the kernel.  If __kernel_text_address()
+                     were SYMBOL_EXPORT'd, we could call that and be
+                     more sure. */
+                } 
+#endif
+            }
+            preempt_enable_no_resched();
+          }
 
 	if (unlikely(m == NULL)) {
+                if (module_name)
+                        _stp_warn ("Missing unwind data for module, rerun with 'stap -d %s'\n",
+                                   module_name); 
 		// Don't _stp_warn about this, will use fallback unwinder.
 		dbug_unwind(1, "No module found for pc=%lx", pc);
 		return -EINVAL;
@@ -1301,6 +1321,12 @@ static int unwind(struct unwind_context *context,
 			      m->eh_frame_len, 1);
 	}
 
+        /* This situation occurs where some unwind data was found, but
+           it was lacking somehow.  */
+        if (res != 0) {
+                dbug_unwind (2, "unwinding failed: %d\n", res);
+        }
+
 	return res;
 }
 
-- 
2.43.5