This is the mail archive of the gdb-patches@sourceware.org mailing list for the GDB project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

fix bogus virtual base pointer adjustment


This code is obviously bogus for:

1) assuming endianness/layout of the value contents buffer
2) assuming vbase offset is always < 256
3) directly changing a value in-place in a value-print
   routine (thus corrupting values in the value history).

Before:

 print virtual_middle_b
 $7 = (Virtual *) 0x603640
 (gdb) PASS: gdb.cp/virtbase.exp: print virtual_middle_b
 print $
 $8 = (VirtualMiddleB *) 0x603640
 (gdb) FAIL: gdb.cp/virtbase.exp: print $
 print *$$
 $9 = {<error reading variable>
 (gdb) FAIL: gdb.cp/virtbase.exp: print *$$

After:

 print virtual_middle_b
 $7 = (Virtual *) 0x603140
 (gdb) PASS: gdb.cp/virtbase.exp: print virtual_middle_b
 print $
 $8 = (Virtual *) 0x603140
 (gdb) PASS: gdb.cp/virtbase.exp: print $
 print *$$
 $9 = (Virtual) {<VirtualMiddleA> = {<VirtualBase> = {_vptr.VirtualBase = 0x401380, x = 0}, _vptr.VirtualMiddleA = 0x401358, y = {0 <repeats 300 times>}}, <VirtualMiddleB> = {_vptr.VirtualMiddleB = 0x4013b0, y = 0}, _vptr.Virtual = 0x401328, z = 0}

Tested on x86_64-linux and applied.  New test included.

-- 
Pedro Alves

2011-02-02  Pedro Alves  <pedro@codesourcery.com>

	gdb/
	* c-valprint.c (c_value_print): When doing virtual base pointer
	adjustment, create a new value with adjusted contents rather than
	changing the contents of the value being printed (and getting it
	wrong).

	gdb/testsuite/
	* gdb.cp/virtbase.cc (VirtualBase, VirtualMiddleA, VirtualMiddleB)
	(Virtual): New structs.
	(virtual_o, virtual_middle_b): New globals.
	* gdb.cp/virtbase.exp: New tests.

---
 gdb/c-valprint.c                  |    3 +--
 gdb/testsuite/gdb.cp/virtbase.cc  |   31 +++++++++++++++++++++++++++++++
 gdb/testsuite/gdb.cp/virtbase.exp |   15 +++++++++++++++
 3 files changed, 47 insertions(+), 2 deletions(-)

Index: src/gdb/testsuite/gdb.cp/virtbase.cc
===================================================================
--- src.orig/gdb/testsuite/gdb.cp/virtbase.cc	2011-02-02 12:29:02.657898995 +0000
+++ src/gdb/testsuite/gdb.cp/virtbase.cc	2011-02-02 16:32:15.007899002 +0000
@@ -88,6 +88,37 @@ public:
   RTTI_data() : data(1) {}
 };
 
+/* These classes are for testing pointer adjustment when printing a
+   pointer into a virtual base, with print object on.  */
+struct VirtualBase {
+  int x;
+
+  virtual ~VirtualBase() {}
+};
+
+struct VirtualMiddleA : public virtual VirtualBase {
+  /* Make sure the vbase offset of Virtual::VirtualBaseB is larger
+     than what fits in one byte.  */
+  int y[300];
+
+  virtual ~VirtualMiddleA() {}
+};
+
+struct VirtualMiddleB : public virtual VirtualBase {
+  int y;
+
+  virtual ~VirtualMiddleB() {}
+};
+
+struct Virtual : public virtual VirtualMiddleA, public virtual VirtualMiddleB {
+  int z;
+
+  virtual ~Virtual() {}
+};
+
+Virtual virtual_o;
+VirtualMiddleB *virtual_middle_b = &virtual_o;
+
 int main() {
   ph::Derived tst;
   tst.get_y();
Index: src/gdb/testsuite/gdb.cp/virtbase.exp
===================================================================
--- src.orig/gdb/testsuite/gdb.cp/virtbase.exp	2011-02-02 12:29:02.657898995 +0000
+++ src/gdb/testsuite/gdb.cp/virtbase.exp	2011-02-02 16:32:15.007899002 +0000
@@ -65,3 +65,18 @@ gdb_test "print/x b->mA" " = 0xaaaaaaaa"
 # https://bugzilla.redhat.com/show_bug.cgi?id=606660
 # `set print object on' is expected.
 gdb_test "print rtti_data" " = .*, data = 1\}"
+
+# Printing a pointer into a virtual base of a larger object used to do
+# pointer adjusment directly into the value being printed, in-place
+# (and did it wrong, too).  Print the pointer, and then access the
+# value history to check the pointer value is not changed.  If it had
+# been changed, then we'd not be able to find the real type anymore.
+gdb_test "print virtual_middle_b" \
+    " = \\(Virtual \\*\\) $hex" \
+    "print pointer to virtual base at non-zero offset of larger object"
+gdb_test "print $" \
+    " = \\(Virtual \\*\\) $hex" \
+    "print same pointer from history value"
+gdb_test "print *$$" \
+    " = \\(Virtual\\) {<VirtualMiddleA> = {<VirtualBase> = {_vptr.VirtualBase = $hex, x = 0}, _vptr.VirtualMiddleA = $hex, y = \\{0 <repeats 300 times>\\}}, <VirtualMiddleB> = {_vptr.VirtualMiddleB = $hex, y = 0}, _vptr.Virtual = $hex, z = 0}" \
+    "print whole pointed-to object, starting from the virtual base pointer"
Index: src/gdb/c-valprint.c
===================================================================
--- src.orig/gdb/c-valprint.c	2011-02-02 12:29:02.897899000 +0000
+++ src/gdb/c-valprint.c	2011-02-02 16:32:15.007899003 +0000
@@ -706,8 +706,7 @@ c_value_print (struct value *val, struct
                   type = lookup_reference_type (real_type);
                 }
 	      /* JYG: Need to adjust pointer value.  */
-	      /* NOTE: cagney/2005-01-02: THIS IS BOGUS.  */
-              value_contents_writeable (val)[0] -= top;
+	      val = value_from_pointer (type, value_as_address (val) - top);
 
               /* Note: When we look up RTTI entries, we don't get any 
                  information on const or volatile attributes.  */


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]