Few weeks back, we have observed "an unexpected process termination" crash in a WPF app. From the crash dump, provides below callstack and unfortunately it was a a memory corruption
00 006fea30 77172e5c 0x770f7000
01 006fea30 56d0df34 ntdll!NtTerminateProcess+0xc
02 006fea30 56d0b9bc verifier!VerifierStopMessage+0x344
03 006fea9c 56d0bdda verifier!AVrfpDphReportCorruptedBlock+0x2fc
04 006feaf8 56d0c2d2 verifier!AVrfpDphCheckNormalHeapBlock+0x11a
05 006feb18 56d0ab23 verifier!AVrfpDphNormalHeapFree+0x22
06 006feb3c 771dfa16 verifier!AVrfDebugPageHeapFree+0xe3
07 006feba4 77143d76 ntdll!RtlDebugFreeHeap+0x3e
08 006fed00 77187add ntdll!RtlpFreeHeap+0xd6
09 006fed5c 77143c46 ntdll!RtlpFreeHeapInternal+0x783
0a 006fed78 754e3320 ntdll!RtlFreeHeap+0x46
0b (Inline) -------- combase!CRetailMalloc_Free+0x16 [onecore\com\combase\class\memapi.cxx @ 656]
0c 006fed90 723cf422 combase!CoTaskMemFree+0x30 [onecore\com\combase\class\memapi.cxx @ 445]
0d 006fedc4 08ef0bc0 mscorlib_ni!System.StubHelpers.CSTRMarshaler.ClearNative+0x2e [f:\dd\ndp\clr\src\BCL\system\stubhelpers.cs @ 125]
0e 006fee6c 08ef0937 0x8ef0bc0
0f 006fee84 08ef08c3 CppAndCs!CppAndCs.Program.GetNativeBuffer+0x4f
10 006fee98 73df0556 CppAndCs!CppAndCs.Program.Main+0x23
11 006feea4 73df373a clr!CallDescrWorkerInternal+0x34
12 006feef8 73df9adb clr!CallDescrWorkerWithHandler+0x6b
13 006fef6c 73f6ff6b clr!MethodDescCallSite::CallTargetWorker+0x16a
14 006ff090 73f7064a clr!RunMain+0x1b3
15 006ff2fc 73f70577 clr!Assembly::ExecuteMainMethod+0xf7
16 006ff7e0 73f706f8 clr!SystemDomain::ExecuteMainMethod+0x5ef
17 006ff838 73f7081e clr!ExecuteEXE+0x4c
18 006ff878 73f6c225 clr!_CorExeMainInternal+0xdc
19 006ff8b4 74dffa84 clr!_CorExeMain+0x4d
1a 006ff8ec 74f0e81e mscoreei!_CorExeMain+0xd6
1b 006ff8fc 74f14338 MSCOREE!ShellShim__CorExeMain+0x9e
1c 006ff914 76cefcc9 MSCOREE!_CorExeMain_Exported+0x8
1d 006ff914 77167c5e KERNEL32!BaseThreadInitThunk+0x19
1e 006ff970 77167c2e ntdll!__RtlUserThreadStart+0x2f
1f 006ff980 00000000 ntdll!_RtlUserThreadStart+0x1b
From the callstack, its clear that, it happens when CLR marshaller tries to free the native memory which is temporarily allocated. The methods are defined as shown below.
C#
[DllImport("CppAndCs.dll", EntryPoint = "GetNativeBuffer",
CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
public static extern string GetNativeBuffer(StringBuilder buffer, IntPtr buuferSize);
C++
void GetNativeBuffer (char *buffer, std::size_t buufer_size);
You may have already figured out the problem. Yes, the return value. CLR’s Interop Marshaler is trying to release memory allocated for return value because C# declaration return type is string. In this case, native method does not have any return value so, CLR try to release unallocated memory and Boom!.
Fix
===
[DllImport("CppAndCs.dll", EntryPoint = "GetNativeBuffer",
CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
public static extern void GetNativeBuffer(StringBuilder buffer, IntPtr buuferSize);
The correct way to return a value from native is to allocate it in native method implementation which will be freed by CLR’s Interop Marshaler later to avoid memory leak
References
========
https://learn.microsoft.com/en-us/dotnet/standard/native-interop/best-practices
https://limbioliong.wordpress.com/2011/06/16/returning-strings-from-a-c-api/
