Re: [libvirt] alignment of data fields when compiling with mingwin

You are perfectly right, I have to find the way to avoid C# memory freeing ! You're a master ;) Arnaud -------------------------------------------------- From: "Matthias Bolte" <matthias.bolte(a)googlemail.com&gt; Sent: Sunday, October 17, 2010 3:21 PM To: <arnaud.champion(a)devatom.fr&gt; Cc: <libvir-list(a)redhat.com&gt; Subject: Re: [libvirt] alignment of data fields when compiling with mingwin > 2010/10/17  &lt;arnaud.champion(a)devatom.fr&gt;: >> >> Hi Matthias, >> >> I'm working on the virConnectOpenAuth method C# binding. And in fact, It >> partially work. Let me explain you : >> > > >> Now, I have made a little code to connect to an esx hypervisor like this >> : >> >> ... some init stuff... >> >>          // Define the virConnectAuth struct >>          virConnectAuth auth = new virConnectAuth >>          { >>              cbdata = authDataPtr, >>              cb = AuthCallback, >>              credtypes = credtypesPtr, >>              ncredtype = (uint)credtypes.Length >>          }; >> >>          IntPtr conn = libVirt.virConnectOpenAuth(tbURI.Text, ref auth, >> 0); >> >> I have the call back method "AuthCallback" defined like this : >> >>      private int AuthCallback(IntPtr creds, uint ncred, IntPtr cbdata) >>      { >> >>          AuthData authData = (AuthData) Marshal.PtrToStructure(cbdata, >> typeof (AuthData)); >>          int offset = 0; >>          int credIndex = 0; >> >>          while (credIndex < ncred) >>          { >>              IntPtr currentCred = new IntPtr(creds.ToInt32() + offset); >> >>              virConnectCredential cred = (virConnectCredential) >> Marshal.PtrToStructure(currentCred, typeof (virConnectCredential)); >>              offset += Marshal.SizeOf(cred); >>              switch(cred.type) >>              { >>                  case virConnectCredentialType.VIR_CRED_AUTHNAME: >>                      cred.result = authData.user_name; >>                      cred.resultlen = (uint)authData.user_name.Length; >>                      break; >>                  case virConnectCredentialType.VIR_CRED_PASSPHRASE: >>                      cred.result = authData.password; >>                      cred.resultlen = (uint) authData.password.Length; >>                      break; >>                  default: >>                      return -1; >>              } >>              Marshal.StructureToPtr(cred, currentCred, true); >> >>              credIndex++; >>          } >>          return 0; >>      } >> >> When I test this code, all seems to work well, I mean the "AuthCallback" >> method is called twice, once for authname and once for passphrase. >> >> But when I run my code in a debugger of Visual Studio I have these >> messages >> : >> >> HEAP[Win32_virConnectOpenAuth.exe]: Invalid address specified to >> RtlFreeHeap( 00700000, 00EE6D78 ) >> HEAP[Win32_virConnectOpenAuth.exe]: Invalid address specified to >> RtlFreeHeap( 00700000, 00EE6A80 ) >> HEAP[Win32_virConnectOpenAuth.exe]: Invalid address specified to >> RtlFreeHeap( 00700000, 00EE6D78 ) >> HEAP[Win32_virConnectOpenAuth.exe]: Invalid address specified to >> RtlFreeHeap( 00700000, 00EE6A80 ) >> HEAP[Win32_virConnectOpenAuth.exe]: Invalid address specified to >> RtlFreeHeap( 00EE0000, 007DE480 ) >> >> but the connection is done, and I am able to list domains of the >> hypervisor >> for example. The real problem is that this program only work inside the >> the >> visual studio debugger, when I launch the executable without debugger, it >> fails. >> So I am searching why this doesn't work, I want to check the bindings. >> And I >> also want to try to fill the "result" member of the virConnectCredential >> structure directly to understanding what can be the problem. > > > Okay, you see an invalid free call either because free is called on an > initial invalid pointer of because free is called twice on the same > pointer (on the second call the pointer is invalid). > > When you look at the libvirt codebase in src/util/authhelper.c in > virRequestUsername you'll see that the cred.result is returned to the > driver directly without making a copy of it. The driver is then > responsible for freeing this memory. So the ownership of the memory > cred.result points to is transferred from your callback to the driver. > > I think you see a double-free here because libvirt and C# are both > trying to free the same memory, but C# should not do this. I'm not > familiar with C#, so I'm just guessing here based on what you have > described. This cannot be a problem with the alignment or struct > layout, otherwise authentication would not work. > > You can test if it's double-free by applying the attached patch to > libvirt. This patch stops the virRequestUsername and > virRequestPassword functions from transferring ownership of the > cred.result by copying the string. This creates a memory leak in the > normal case, but should stop the double-free in case C# is freeing > cred.result here. > > Matthias > > >> Anyway, thanks ofr these informations, this can help. >> >> Best regards, >> >> Arnaud >> >> -------------------------------------------------- >> From: "Matthias Bolte" <matthias.bolte(a)googlemail.com&gt; >> Sent: Sunday, October 17, 2010 12:04 PM >> To: <arnaud.champion(a)devatom.fr&gt; >> Cc: <libvir-list(a)redhat.com&gt; >> Subject: Re: [libvirt] alignment of data fields when compiling with >> mingwin >> >>> 2010/10/15  &lt;arnaud.champion(a)devatom.fr&gt;: >>>> >>>> Hi, >>>> >>>> I'm currently working on libvirt csharp bindings, and I have some >>>> trouble >>>> with virConnectOpenAuth marshaling. >>>> I need to know what is the alignment of data fields in structure when >>>> compiling with mingwin. >>>> Anyone know that ? >>>> >>>> cheers, >>>> >>>> Arnaud Champion >>>> >>> >>> Why do you need to know the alignment? Do you need to build or access >>> members of the virConnectCredential or virConnectAuth structs by >>> offset in memory? >>> >>> The Wikipedia article about data structure alignment might be helpful >>> when you really need to care about alignment. >>> >>> If you actually need the offset of the members in those structs you >>> can just use the offsetof macro and let the compiler tell you: >>> >>> #include <stdio.h> >>> #include <stddef.h> >>> #include <libvirt/libvirt.h> >>> >>> void main(void) >>> { >>>  printf("virConnectCredential\n"); >>>  printf("  type      %2u\n", offsetof(virConnectCredential, type)); >>>  printf("  prompt    %2u\n", offsetof(virConnectCredential, prompt)); >>>  printf("  challenge %2u\n", offsetof(virConnectCredential, challenge)); >>>  printf("  defresult %2u\n", offsetof(virConnectCredential, defresult)); >>>  printf("  result    %2u\n", offsetof(virConnectCredential, result)); >>>  printf("  resultlen %2u\n", offsetof(virConnectCredential, resultlen)); >>>  printf("\n"); >>>  printf("virConnectAuth\n"); >>>  printf("  credtype  %2u\n", offsetof(virConnectAuth, credtype)); >>>  printf("  ncredtype %2u\n", offsetof(virConnectAuth, ncredtype)); >>>  printf("  cb        %2u\n", offsetof(virConnectAuth, cb)); >>>  printf("  cbdata    %2u\n", offsetof(virConnectAuth, cbdata)); >>> } >>> >>> >>> Output on x86: >>> >>> virConnectCredential >>>  type       0 >>>  prompt     4 >>>  challenge  8 >>>  defresult 12 >>>  result    16 >>>  resultlen 20 >>> >>> virConnectAuth >>>  credtype   0 >>>  ncredtype  4 >>>  cb         8 >>>  cbdata    12 >>> >>> >>> Output on x86_64: >>> >>> virConnectCredential >>>  type       0 >>>  prompt     8 >>>  challenge 16 >>>  defresult 24 >>>  result    32 >>>  resultlen 40 >>> >>> virConnectAuth >>>  credtype   0 >>>  ncredtype  8 >>>  cb        16 >>>  cbdata    24 >>> >>> [1] >>> >>> http://en.wikipedia.org/wiki/Data_structure_alignment#Typical_alignment_o... >>> >>> Matthias >> >> >> >