From 228af5c49c06079e6bfe1daa64ead51b1dc979c7 Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mjw@redhat.com>
Date: Mon, 16 Nov 2009 10:02:50 +0100
Subject: [PATCH] PR10622 Search for extern $variables in symbol table.

* dwflpp.h (vardie_from_symtable): New method.
* dwflpp.cxx (vardie_from_symtable): New method.
  (literal_stmt_for_local): Use vardie_from_symtable when no location
  attribute and DW_AT_external.
* testsuite/buildok/xtime.stp: New testcase from PR10622.
---
 dwflpp.cxx                  | 68 +++++++++++++++++++++++++++++--------
 dwflpp.h                    |  1 +
 testsuite/buildok/xtime.stp |  7 ++++
 3 files changed, 62 insertions(+), 14 deletions(-)
 create mode 100755 testsuite/buildok/xtime.stp

diff --git a/dwflpp.cxx b/dwflpp.cxx
index fbfe3f94e..92fe04c1d 100644
--- a/dwflpp.cxx
+++ b/dwflpp.cxx
@@ -2210,6 +2210,34 @@ dwflpp::express_as_string (string prelude,
   return result;
 }
 
+Dwarf_Addr
+dwflpp::vardie_from_symtable (Dwarf_Die *vardie, Dwarf_Addr *addr)
+{
+  const char *name = dwarf_diename (vardie);
+  if (sess.verbose > 2)
+    clog << "finding symtable address for " << name << "\n";
+
+  *addr = 0;
+  int syms = dwfl_module_getsymtab (module);
+  dwfl_assert ("Getting symbols", syms >= 0);
+
+  for (int i = 0; *addr == 0 && i < syms; i++)
+    {
+      GElf_Sym sym;
+      GElf_Word shndxp;
+      const char *symname = dwfl_module_getsym(module, i, &sym, &shndxp);
+      if (symname
+	  && ! strcmp (name, symname)
+	  && sym.st_shndx != SHN_UNDEF
+	  && GELF_ST_TYPE (sym.st_info) == STT_OBJECT)
+	*addr = sym.st_value;
+    }
+
+  if (sess.verbose > 2)
+    clog << "found " << name << "@0x" << hex << *addr << "\n";
+
+  return *addr;
+}
 
 string
 dwflpp::literal_stmt_for_local (vector<Dwarf_Die>& scopes,
@@ -2231,30 +2259,42 @@ dwflpp::literal_stmt_for_local (vector<Dwarf_Die>& scopes,
          << ", module bias 0x" << module_bias << dec
          << "\n";
 
+#define obstack_chunk_alloc malloc
+#define obstack_chunk_free free
+
+  struct obstack pool;
+  obstack_init (&pool);
+  struct location *tail = NULL;
+
+  /* Given $foo->bar->baz[NN], translate the location of foo. */
+
+  struct location *head;
+
   Dwarf_Attribute attr_mem;
   if (dwarf_attr_integrate (&vardie, DW_AT_const_value, &attr_mem) == NULL
       && dwarf_attr_integrate (&vardie, DW_AT_location, &attr_mem) == NULL)
     {
-      throw semantic_error("failed to retrieve location "
+      Dwarf_Op addr_loc;
+      addr_loc.atom = DW_OP_addr;
+      // If it is an external variable try the symbol table. PR10622.
+      if (dwarf_attr_integrate (&vardie, DW_AT_external, &attr_mem) != NULL
+	  && vardie_from_symtable (&vardie, &addr_loc.number) != 0)
+	{
+	  head = c_translate_location (&pool, &loc2c_error, this,
+				       &loc2c_emit_address,
+				       1, 0, pc,
+				       NULL, &addr_loc, 1, &tail, NULL, NULL);
+	}
+      else
+	throw semantic_error("failed to retrieve location "
                            "attribute for local '" + local
                            + "' (dieoffset: "
                            + lex_cast_hex(dwarf_dieoffset (&vardie))
                            + ")",
                            e->tok);
     }
-
-#define obstack_chunk_alloc malloc
-#define obstack_chunk_free free
-
-  struct obstack pool;
-  obstack_init (&pool);
-  struct location *tail = NULL;
-
-  /* Given $foo->bar->baz[NN], translate the location of foo. */
-
-  struct location *head = translate_location (&pool,
-                                              &attr_mem, pc, fb_attr, &tail,
-                                              e);
+  else
+    head = translate_location (&pool, &attr_mem, pc, fb_attr, &tail, e);
 
   if (dwarf_attr_integrate (&vardie, DW_AT_type, &attr_mem) == NULL)
     throw semantic_error("failed to retrieve type "
diff --git a/dwflpp.h b/dwflpp.h
index 226b84d86..b3f71eb27 100644
--- a/dwflpp.h
+++ b/dwflpp.h
@@ -394,6 +394,7 @@ private:
   // Returns the call frame address operations for the given program counter.
   Dwarf_Op *get_cfa_ops (Dwarf_Addr pc);
 
+  Dwarf_Addr vardie_from_symtable(Dwarf_Die *vardie, Dwarf_Addr *addr);
 };
 
 #endif // DWFLPP_H
diff --git a/testsuite/buildok/xtime.stp b/testsuite/buildok/xtime.stp
new file mode 100755
index 000000000..e41f9b164
--- /dev/null
+++ b/testsuite/buildok/xtime.stp
@@ -0,0 +1,7 @@
+#! stap -p4
+
+# Test for getting at an external global variable PR10622
+probe kernel.function("do_gettimeofday")
+{
+  printf("xtime.tv_sec:%d\n", $xtime->tv_sec); exit();
+}
-- 
2.43.5