Crash Dump Analysis Patterns (Part 49)

Frame Pointer Omission pattern is the most visible compiler optimization technique and you can notice it in verbose stack traces:

0:000> kv
ChildEBP RetAddr
0012ee10 004737a7 application!MemCopy+0x17 (FPO: [3,0,2])
0012ef0c 35878c5b application!ProcessData+0×97 (FPO: [Uses EBP] [3,59,4])
WARNING: Frame IP not in any known module. Following frames may be wrong.
0012ef1c 72a0015b 0×35878c5b
0012ef20 a625e1b0 0×72a0015b
0012ef24 d938bcfe 0xa625e1b0
0012ef28 d4f91bb4 0xd938bcfe
0012ef2c c1c035ce 0xd4f91bb4

To recall FPO is a compiler optimization where ESP register is used to address local variables and parameters instead of EBP. EBP may or may not be used for other purposes. When it is used you will notice

FPO: [Uses EBP]

as in the trace above. For description of other FPO number triplets please see Debugging Tools for Windows help section “k, kb, kd, kp, kP, kv (Display Stack Backtrace)”

Running analysis command points to possible stack corruption:



00438637 f3a5 rep movs dword ptr es:[edi],dword ptr [esi]

Looking at EBP and ESP shows that they are mismatched:

0:000> r
eax=00000100 ebx=00a027f3 ecx=00000040 edx=0012ee58 esi=d938bcfe edi=0012ee58
eip=00438637 esp=0012ee0c ebp=00a02910 iopl=0 nv up ei pl nz na po nc
cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000 efl=00000202
00438637 f3a5 rep movs dword ptr es:[edi],dword ptr [esi] es:0023:0012ee58=00000010 ds:0023:d938bcfe=????????

We might think about Local Buffer Overflow pattern here but two top stack trace lines are in accordance with each other:

0:000> ub 004737a7
00473790 cmp     eax,edi
00473792 jb      application!ProcessData+0x72 (00473782)
00473794 mov     ecx,dword ptr [esp+104h]
0047379b push    esi
0047379c lea     edx,[esp+38h]
004737a0 push    ecx
004737a1 push    edx
004737a2 call    application!MemCopy (00438620)

So perhaps EBP value differs greatly from ESP due to its usage as general purpose register and in fact there was no any stack corruption. Despite using public symbols we have the instance of Incorrect Stack Trace pattern and we might want to reconstruct it manually. Let’s search for EBP value on raw stack below the crash point:

0:000> !teb
TEB at 7ffdf000
    ExceptionList:        0012ffb0
    StackBase:            00130000
    StackLimit:           00126000
    SubSystemTib:         00000000
    FiberData:            00001e00
    ArbitraryUserPointer: 00000000
    Self:                 7ffdf000
    EnvironmentPointer:   00000000
    ClientId:             0000660c . 00005890
    RpcHandle:            00000000
    Tls Storage:          00000000
    PEB Address:          7ffd9000
    LastErrorValue:       0
    LastStatusValue:      0
    Count Owned Locks:    0
    HardErrorMode:        0

0:000> dds  00126000 00130000
00126000  00000000
00126004  00000000
00126008  00000000
0012eb0c  00a02910
0012eb10  7c90e25e ntdll!NtRaiseException+0xc
0012eb14  7c90eb15 ntdll!KiUserExceptionDispatcher+0x29
0012eb18  0012eb24
0012eb1c  0012eb40
0012eb20  00000000
0012eb24  c0000005
0012eb28  00000000
0012eb2c  00000000
0012eb30  00438637 application!MemCopy+0x17
0012eb34  00000002
0012eb38  00000000
0012eb3c  d938bcfe
0012ebf4  00a02910
0012ebf8  00438637 application!MemCopy+0×17
0012ebfc  0000001b

0012f134  00436323 application!ConstructInfo+0×113
0012f138  00a02910
0012f13c  0000011c

Let’s see what functions ConstructInfo calls:

0:000> ub 00436323
00436313 lea     edx,[esp+10h]
00436317 push    edx
00436318 push    eax
00436319 push    30h
0043631b push    ecx
0043631c push    ebx
0043631d push    ebp
0043631e call    application!EnvelopeData (00438bf0)

We notice EBP was pushed prior to calling EnvelopeData. If we disassemble this function we would see that it calls ProcessData from our partial stack trace: 

0:000> uf 00438bf0
00438bf0 sub     esp,1F4h
00438bf6 push    ebx
00438bf7 mov     ebx,dword ptr [esp+20Ch]
00438bfe test    ebx,ebx
00438c00 push    ebp
00438c76 rep stos byte ptr es:[edi]
00438c78 lea     eax,[esp+14h]
00438c7c push    eax
00438c7d push    ebp
00438c7e call    application!ProcessData (00473710)
00438c83 pop     edi
00438c84 pop     esi

Let’s try elaborate form of k command and supply it with custom ESP and EBP values pointing to

0012f134  00436323 application!ConstructInfo+0×113

and also EIP of the fault:

0:000> k L=0012f134 0012f134 00438637
ChildEBP RetAddr 
0012f1cc 00435a65 application!MemCopy+0×17
0012f28c 0043532e application!ClientHandleServerRequest+0×395
0012f344 00434fcd application!Accept+0×23
0012f374 0042e4f3 application!DataArrival+0×17d
0012f43c 0041aea9 application!ProcessInput+0×98
0012ff0c 0045b278 application!AppMain+0xda
0012ff24 0041900e application!WinMain+0×78
0012ffc0 7c816fd7 application!WinMainCRTStartup+0×134
0012fff0 00000000 kernel32!BaseProcessStart+0×23

We see that although it misses some initial frames after MemCopy we aided WinDbg to walk to the bottom of the stack and reconstruct the plausible stack trace for us.

- Dmitry Vostokov @ -

One Response to “Crash Dump Analysis Patterns (Part 49)”

  1. Crash Dump Analysis » Blog Archive » Icons for Memory Dump Analysis Patterns (Part 81) Says:

    […] Debugging Experts Magazine Online Today we introduce an icon for Frame Pointer Omission pattern: […]

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