[Mono-bugs] [Bug 457257] New: Compiler crashes trying to find a member to override

bugzilla_noreply at novell.com bugzilla_noreply at novell.com
Mon Dec 8 09:57:48 EST 2008


           Summary: Compiler crashes trying to find a member to override
           Product: Mono: Compilers
           Version: SVN
          Platform: x86-64
        OS/Version: Ubuntu
            Status: NEW
          Severity: Major
          Priority: P5 - None
         Component: C#
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: michiel at eurotrol.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: Customer

Description of Problem:
The compiler crashes with a null reference exception when trying to compile the
programme below

Steps to reproduce the problem:
1. Create a file "test.cs" (name not important) with the following content:
-------- START FILE --------------
namespace ETDB
public class Exception : System.Exception
        string _message="";

        public Exception(string msg)
                _message = msg;

        public string message
                get { return _message; }
--------- END FILE ---------------
2. Then compile the file using
gmcs -pkg:dotnet -target:library -debug -out:test.dll test.cs

Actual Results:
Unhandled Exception: Mono.CSharp.InternalErrorException: test.cs(12,23):
ETDB.Exception.message ---> System.NullReferenceException: Object reference not
set to an instance of an object
  at Mono.CSharp.MemberCache.FindMemberToOverride (System.Type invocation_type,
System.String name, Mono.CSharp.AParametersCollection parameters,
Mono.CSharp.GenericMethod generic_method, Boolean is_property) [0x00000] 
  at Mono.CSharp.Property.ResolveBaseProperty () [0x00000] 
  at Mono.CSharp.PropertyBase.FindOutBaseMethod (System.Type& base_ret_type)
  at Mono.CSharp.InterfaceMemberBase.CheckBase () [0x00000] 
  at Mono.CSharp.Property.Define () [0x00000] 
  at Mono.CSharp.TypeContainer+MemberCoreArrayList.DefineContainerMembers ()
  --- End of inner exception stack trace ---
  at Mono.CSharp.TypeContainer+MemberCoreArrayList.DefineContainerMembers ()
  at Mono.CSharp.TypeContainer.DefineContainerMembers
(Mono.CSharp.MemberCoreArrayList mcal) [0x00000] 
  at Mono.CSharp.Class.DefineContainerMembers (Mono.CSharp.MemberCoreArrayList
list) [0x00000] 
  at Mono.CSharp.TypeContainer.DoDefineMembers () [0x00000] 
  at Mono.CSharp.Class.DoDefineMembers () [0x00000] 
  at Mono.CSharp.TypeContainer.Define () [0x00000] 
  at Mono.CSharp.ClassOrStruct.Define () [0x00000] 
  at Mono.CSharp.Class.Define () [0x00000] 
  at Mono.CSharp.RootContext.PopulateTypes () [0x00000] 
  at Mono.CSharp.Driver.Compile () [0x00000] 
  at Mono.CSharp.Driver.Main (System.String[] args) [0x00000] 

Expected Results:
A file called test.dll with a namespace specific exception object.

How often does this happen? 

Additional Information:
FindMemberToOverride is called with is_property set true.
In the method-chain-walk-loop, the mi variable is initialised null and remains
null because of is_property. The switch then jumps to case
FieldAttributes.Assembly/FieldAttributes.FamANDAssem, which accesses a member
of the mi object.

Patch as follows on mono-118180:
--- mcs/mcs/decl.cs     2008-12-02 12:59:11.000000000 +0100
+++ mcs/mcs/decl.cs.ori 2008-12-02 09:51:58.000000000 +0100
@@@ -2381,7 +2383,7 @@
                                                // Check for assembly methods
-                                               if (mi!= null &&
mi.DeclaringType.Assembly != CodeGen.Assembly.Builder)
+                                               if (mi.DeclaringType.Assembly
!= CodeGen.Assembly.Builder)

Please note, I did not check if this should have been:

    if (mi != null && mi.DeclaringType.Assembly != CodeGen.Assembly.Builder)


    if (mi == null || mi.DeclaringType.Assembly != CodeGen.Assembly.Builder)

The former seems to produce working output in my production environment,
although it was not stress-tested.

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