PR10067: fix bitfield access

	* tapsets.cxx (dwflpp::translate_components): Eliminate the extra
	die-dereference at the end of the loop (a regression from @casts).
	* runtime/loc2c-runtime.h (store_bitfield): Use the target as the
	representative type, since the base is always int64_t.  Also be a
	bit more aggressive with masking and parentheses.
	* testsuite/systemtap.base/bitfield.*: New test for R/W bitfields.

4 files changed, 60 insertions, 7 deletions

diff --git a/runtime/loc2c-runtime.h b/runtime/loc2c-runtime.h
index eaf47cad..620e1615 100644
--- a/runtime/loc2c-runtime.h
+++ b/runtime/loc2c-runtime.h
@@ -29,11 +29,12 @@
 	    & (((__typeof (base)) 1 << (nbits)) - 1))
 
 #define store_bitfield(target, base, higherbits, nbits)			      \
-  target = (target							      \
-	    &~ ((((__typeof (base)) 1 << (nbits)) - 1)			      \
-		<< (sizeof (base) * 8 - (higherbits) - (nbits)))	      \
-	    | ((__typeof (base)) (base)					      \
-	       << (sizeof (base) * 8 - (higherbits) - (nbits))))
+  target = ((target							      \
+	     &~ ((((__typeof (target)) 1 << (nbits)) - 1)		      \
+		 << (sizeof (target) * 8 - (higherbits) - (nbits))))	      \
+	    | ((((__typeof (target)) (base))				      \
+		& (((__typeof (target)) 1 << (nbits)) - 1))		      \
+	       << (sizeof (target) * 8 - (higherbits) - (nbits))))
 
 
 /* Given a DWARF register number, fetch its intptr_t (long) value from the
diff --git a/tapsets.cxx b/tapsets.cxx
index 094ae358..c63151e1 100644
--- a/tapsets.cxx
+++ b/tapsets.cxx
@@ -2006,7 +2006,7 @@ struct dwflpp
 		       Dwarf_Die *die_mem,
 		       Dwarf_Attribute *attr_mem)
   {
-    Dwarf_Die *die = die_mem;
+    Dwarf_Die *die = NULL;
     Dwarf_Die struct_die;
     Dwarf_Attribute temp_attr;
 
@@ -2015,6 +2015,9 @@ struct dwflpp
     if (vardie)
       *die_mem = *vardie;
 
+    if (e->components.empty())
+      return die_mem;
+
     static unsigned int func_call_level ;
     static unsigned int dwarf_error_flag ; // indicates current error is dwarf error
     static unsigned int dwarf_error_count ; // keeps track of no of dwarf errors
@@ -2031,6 +2034,7 @@ struct dwflpp
         obstack_printf (pool, "c->last_stmt = %s;", lex_cast_qstring(piece).c_str());
 #endif
 
+	die = die ? dwarf_formref_die (attr_mem, die_mem) : die_mem;
 	const int typetag = dwarf_tag (die);
 	switch (typetag)
 	  {
@@ -2188,7 +2192,6 @@ struct dwflpp
 	/* Now iterate on the type in DIE's attribute.  */
 	if (dwarf_attr_integrate (die, DW_AT_type, attr_mem) == NULL)
 	  throw semantic_error ("cannot get type of field: " + string(dwarf_errmsg (-1)), e->tok);
-	die = dwarf_formref_die (attr_mem, die_mem);
       }
     return die;
   }
diff --git a/testsuite/systemtap.base/bitfield.exp b/testsuite/systemtap.base/bitfield.exp
new file mode 100644
index 00000000..16451369
--- /dev/null
+++ b/testsuite/systemtap.base/bitfield.exp
@@ -0,0 +1,3 @@
+# test that bitfield r/w works correctly
+set test "bitfield"
+stap_run $srcdir/$subdir/$test.stp no_load $all_pass_string -g
diff --git a/testsuite/systemtap.base/bitfield.stp b/testsuite/systemtap.base/bitfield.stp
new file mode 100644
index 00000000..c2ff4929
--- /dev/null
+++ b/testsuite/systemtap.base/bitfield.stp
@@ -0,0 +1,46 @@
+%{
+#include <linux/tcp.h>
+static struct tcphdr foo = {0};
+%}
+
+function get_ptr:long() %{ THIS->__retvalue = (long)&foo; /* pure */ %}
+function get_ack:long() %{ THIS->__retvalue = foo.ack; /* pure */ %}
+function get_urg:long() %{ THIS->__retvalue = foo.urg; /* pure */ %}
+
+function check:long(ack:long, urg:long) {
+  ptr = get_ptr()
+
+  /* set the bits with cast */
+  @cast(ptr, "tcphdr")->ack = ack
+  @cast(ptr, "tcphdr")->urg = urg
+
+  /* check that reading with embedded-C is ok */
+  real_ack = get_ack()
+  real_urg = get_urg()
+  errors = (ack != real_ack) + (urg != real_urg)
+
+  /* check that reading with a cast is ok */
+  cast_ack = @cast(ptr, "tcphdr")->ack
+  cast_urg = @cast(ptr, "tcphdr")->urg
+  errors += (ack != cast_ack) + (urg != cast_urg)
+
+  if (errors)
+    printf("bitfield had %d errors; expect(%d%d), real(%d%d), cast(%d%d)\n",
+           errors, ack, urg, real_ack, real_urg, cast_ack, cast_urg)
+
+  return errors
+}
+
+probe begin {
+  println("systemtap starting probe")
+
+  errors = check(0, 0)
+  errors += check(0, 1)
+  errors += check(1, 0)
+  errors += check(1, 1)
+
+  println("systemtap ending probe")
+  if (errors == 0)
+    println("systemtap test success")
+  exit()
+}