(The note below has been copypasted to the Reverse Engineering for Beginners book.)
This is a joke I did once for my coworkers who played a Solitaire game too much. I was wondering, if it's possible to remove some cards, or maybe add (duplicates).
I opened Solitaire.exe in IDA disassembler, which asked if to download PDB file for it from Microsoft servers. This is usually a rule for many Windows executables and DLLs. At least, PDB has all function names.
Then I tried to find a 52 number in all functions (because this card game uses 52 cards). As it turned out, only 2 functions has it.
The first is:
.text:00000001000393B4 ; __int64 __fastcall SolitaireGame::OnMoveComplete(SolitaireGame *this) .text:00000001000393B4 ?OnMoveComplete@SolitaireGame@@QEAAHXZ proc near ...
The second is the function with self-describing name (name pulled from PDB by IDA): InitialDeal():
.text:00000001000365F8 ; void __fastcall SolitaireGame::InitialDeal(SolitaireGame *__hidden this)
.text:00000001000365F8 ?InitialDeal@SolitaireGame@@QEAAXXZ proc near
.text:00000001000365F8
.text:00000001000365F8 var_58 = byte ptr -58h
.text:00000001000365F8 var_48 = qword ptr -48h
.text:00000001000365F8 var_40 = dword ptr -40h
.text:00000001000365F8 var_3C = dword ptr -3Ch
.text:00000001000365F8 var_38 = dword ptr -38h
.text:00000001000365F8 var_30 = qword ptr -30h
.text:00000001000365F8 var_28 = xmmword ptr -28h
.text:00000001000365F8 var_18 = byte ptr -18h
.text:00000001000365F8
.text:00000001000365F8 ; FUNCTION CHUNK AT .text:00000001000A55C2 SIZE 00000018 BYTES
.text:00000001000365F8
.text:00000001000365F8 ; __unwind { // __CxxFrameHandler3
.text:00000001000365F8 mov rax, rsp
.text:00000001000365FB push rdi
.text:00000001000365FC push r12
.text:00000001000365FE push r13
.text:0000000100036600 sub rsp, 60h
.text:0000000100036604 mov [rsp+78h+var_48], 0FFFFFFFFFFFFFFFEh
.text:000000010003660D mov [rax+8], rbx
.text:0000000100036611 mov [rax+10h], rbp
.text:0000000100036615 mov [rax+18h], rsi
.text:0000000100036619 movaps xmmword ptr [rax-28h], xmm6
.text:000000010003661D mov rsi, rcx
.text:0000000100036620 xor edx, edx ; struct Card *
.text:0000000100036622 call ?SetSelectedCard@SolitaireGame@@QEAAXPEAVCard@@@Z ; SolitaireGame::SetSelectedCard(Card *)
.text:0000000100036627 and qword ptr [rsi+0F0h], 0
.text:000000010003662F mov rax, cs:?g_pSolitaireGame@@3PEAVSolitaireGame@@EA ; SolitaireGame * g_pSolitaireGame
.text:0000000100036636 mov rdx, [rax+48h]
.text:000000010003663A cmp byte ptr [rdx+51h], 0
.text:000000010003663E jz short loc_10003664E
.text:0000000100036640 xor r8d, r8d ; bool
.text:0000000100036643 mov dl, 1 ; int
.text:0000000100036645 lea ecx, [r8+3] ; this
.text:0000000100036649 call ?PlaySoundProto@GameAudio@@YA_NH_NPEAI@Z ; GameAudio::PlaySoundProto(int,bool,uint *)
.text:000000010003664E
.text:000000010003664E loc_10003664E: ; CODE XREF: SolitaireGame::InitialDeal(void)+46
.text:000000010003664E mov rbx, [rsi+88h]
.text:0000000100036655 mov r8d, 4
.text:000000010003665B lea rdx, aCardstackCreat ; "CardStack::CreateDeck()::uiNumSuits == "...
.text:0000000100036662 mov ebp, 10000h
.text:0000000100036667 mov ecx, ebp ; unsigned int
.text:0000000100036669 call ?Log@@YAXIPEBGZZ ; Log(uint,ushort const *,...)
.text:000000010003666E mov r8d, 52 ; ---
.text:0000000100036674 lea rdx, aCardstackCreat_0 ; "CardStack::CreateDeck()::uiNumCards == "...
.text:000000010003667B mov ecx, ebp ; unsigned int
.text:000000010003667D call ?Log@@YAXIPEBGZZ ; Log(uint,ushort const *,...)
.text:0000000100036682 xor edi, edi
.text:0000000100036684 loc_100036684: ; CODE XREF: SolitaireGame::InitialDeal(void)+C0
.text:0000000100036684 mov eax, 4EC4EC4Fh
.text:0000000100036689 mul edi
.text:000000010003668B mov r8d, edx
.text:000000010003668E shr r8d, 4 ; unsigned int
.text:0000000100036692 mov eax, r8d
.text:0000000100036695 imul eax, 52 ; ---
.text:0000000100036698 mov edx, edi
.text:000000010003669A sub edx, eax ; unsigned int
.text:000000010003669C mov rcx, [rbx+128h] ; this
.text:00000001000366A3 call ?CreateCard@CardTable@@IEAAPEAVCard@@II@Z ; CardTable::CreateCard(uint,uint)
.text:00000001000366A8 mov rdx, rax ; struct Card *
.text:00000001000366AB mov rcx, rbx ; this
.text:00000001000366AE call ?Push@CardStack@@QEAAXPEAVCard@@@Z ; CardStack::Push(Card *)
.text:00000001000366B3 inc edi
.text:00000001000366B5 cmp edi, 52 ; ---
.text:00000001000366B8 jb short loc_100036684
.text:00000001000366BA xor r8d, r8d ; bool
.text:00000001000366BD xor edx, edx ; bool
.text:00000001000366BF mov rcx, rbx ; this
.text:00000001000366C2 call ?Arrange@CardStack@@QEAAX_N0@Z ; CardStack::Arrange(bool,bool)
.text:00000001000366C7 mov r13, [rsi+88h]
.text:00000001000366CE lea rdx, aCardstackShuff ; "CardStack::Shuffle()"
.text:00000001000366D5 mov ecx, ebp ; unsigned int
.text:00000001000366D7 call ?Log@@YAXIPEBGZZ ; Log(uint,ushort const *,...)
.text:00000001000366DC and [rsp+78h+var_40], 0
.text:00000001000366E1 and [rsp+78h+var_3C], 0
.text:00000001000366E6 mov [rsp+78h+var_38], 10h
.text:00000001000366EE xor ebx, ebx
.text:00000001000366F0 mov [rsp+78h+var_30], rbx
...
Anyway, we clearly see a loop of 52 iterations. A loop body has calls to CardTable()::CreateCard() and CardStack::Push().
The CardTable::CreateCard() eventually calls Card::Init() with values in 0..51 range, as one of its arguments. This can be easily checked using debugger.
So I tried just to change the 52 (0x34) number to 51 (0x33) in the "cmp edi, 52" instruction at 0x1000366B5 and run it. At first glance, nothing happened, but I noticed that now it's hard to solve the game. I spent almost hour to reach this "position":
Ace of hearts is missing. Perhaps, internally, this card is numbered as 51th (if to number them from zero).
In the other place I found all card names. Maybe names to be used to fetch card graphics from resources?
.data:00000001000B6970 ?CARD_NAME@Card@@2PAPEBGA dq offset aTwoofclubs .data:00000001000B6970 ; "TwoOfClubs" .data:00000001000B6978 dq offset aThreeofclubs ; "ThreeOfClubs" .data:00000001000B6980 dq offset aFourofclubs ; "FourOfClubs" .data:00000001000B6988 dq offset aFiveofclubs ; "FiveOfClubs" .data:00000001000B6990 dq offset aSixofclubs ; "SixOfClubs" .data:00000001000B6998 dq offset aSevenofclubs ; "SevenOfClubs" .data:00000001000B69A0 dq offset aEightofclubs ; "EightOfClubs" .data:00000001000B69A8 dq offset aNineofclubs ; "NineOfClubs" .data:00000001000B69B0 dq offset aTenofclubs ; "TenOfClubs" .data:00000001000B69B8 dq offset aJackofclubs ; "JackOfClubs" .data:00000001000B69C0 dq offset aQueenofclubs ; "QueenOfClubs" .data:00000001000B69C8 dq offset aKingofclubs ; "KingOfClubs" .data:00000001000B69D0 dq offset aAceofclubs ; "AceOfClubs" .data:00000001000B69D8 dq offset aTwoofdiamonds ; "TwoOfDiamonds" .data:00000001000B69E0 dq offset aThreeofdiamond ; "ThreeOfDiamonds" .data:00000001000B69E8 dq offset aFourofdiamonds ; "FourOfDiamonds" .data:00000001000B69F0 dq offset aFiveofdiamonds ; "FiveOfDiamonds" .data:00000001000B69F8 dq offset aSixofdiamonds ; "SixOfDiamonds" .data:00000001000B6A00 dq offset aSevenofdiamond ; "SevenOfDiamonds" .data:00000001000B6A08 dq offset aEightofdiamond ; "EightOfDiamonds" .data:00000001000B6A10 dq offset aNineofdiamonds ; "NineOfDiamonds" .data:00000001000B6A18 dq offset aTenofdiamonds ; "TenOfDiamonds" .data:00000001000B6A20 dq offset aJackofdiamonds ; "JackOfDiamonds" .data:00000001000B6A28 dq offset aQueenofdiamond ; "QueenOfDiamonds" .data:00000001000B6A30 dq offset aKingofdiamonds ; "KingOfDiamonds" .data:00000001000B6A38 dq offset aAceofdiamonds ; "AceOfDiamonds" .data:00000001000B6A40 dq offset aTwoofspades ; "TwoOfSpades" .data:00000001000B6A48 dq offset aThreeofspades ; "ThreeOfSpades" .data:00000001000B6A50 dq offset aFourofspades ; "FourOfSpades" .data:00000001000B6A58 dq offset aFiveofspades ; "FiveOfSpades" .data:00000001000B6A60 dq offset aSixofspades ; "SixOfSpades" .data:00000001000B6A68 dq offset aSevenofspades ; "SevenOfSpades" .data:00000001000B6A70 dq offset aEightofspades ; "EightOfSpades" .data:00000001000B6A78 dq offset aNineofspades ; "NineOfSpades" .data:00000001000B6A80 dq offset aTenofspades ; "TenOfSpades" .data:00000001000B6A88 dq offset aJackofspades ; "JackOfSpades" .data:00000001000B6A90 dq offset aQueenofspades ; "QueenOfSpades" .data:00000001000B6A98 dq offset aKingofspades ; "KingOfSpades" .data:00000001000B6AA0 dq offset aAceofspades ; "AceOfSpades" .data:00000001000B6AA8 dq offset aTwoofhearts ; "TwoOfHearts" .data:00000001000B6AB0 dq offset aThreeofhearts ; "ThreeOfHearts" .data:00000001000B6AB8 dq offset aFourofhearts ; "FourOfHearts" .data:00000001000B6AC0 dq offset aFiveofhearts ; "FiveOfHearts" .data:00000001000B6AC8 dq offset aSixofhearts ; "SixOfHearts" .data:00000001000B6AD0 dq offset aSevenofhearts ; "SevenOfHearts" .data:00000001000B6AD8 dq offset aEightofhearts ; "EightOfHearts" .data:00000001000B6AE0 dq offset aNineofhearts ; "NineOfHearts" .data:00000001000B6AE8 dq offset aTenofhearts ; "TenOfHearts" .data:00000001000B6AF0 dq offset aJackofhearts ; "JackOfHearts" .data:00000001000B6AF8 dq offset aQueenofhearts ; "QueenOfHearts" .data:00000001000B6B00 dq offset aKingofhearts ; "KingOfHearts" .data:00000001000B6B08 dq offset aAceofhearts ; "AceOfHearts" .data:00000001000B6B10 ; public: static unsigned short const * near * Card::CARD_HUMAN_NAME .data:00000001000B6B10 ?CARD_HUMAN_NAME@Card@@2PAPEBGA dq offset a54639Cardnames .data:00000001000B6B10 ; "|54639|CardNames|Two Of Clubs" .data:00000001000B6B18 dq offset a64833Cardnames ; "|64833|CardNames|Three Of Clubs" .data:00000001000B6B20 dq offset a62984Cardnames ; "|62984|CardNames|Four Of Clubs" .data:00000001000B6B28 dq offset a65200Cardnames ; "|65200|CardNames|Five Of Clubs" .data:00000001000B6B30 dq offset a52967Cardnames ; "|52967|CardNames|Six Of Clubs" .data:00000001000B6B38 dq offset a42781Cardnames ; "|42781|CardNames|Seven Of Clubs" .data:00000001000B6B40 dq offset a49217Cardnames ; "|49217|CardNames|Eight Of Clubs" .data:00000001000B6B48 dq offset a44682Cardnames ; "|44682|CardNames|Nine Of Clubs" .data:00000001000B6B50 dq offset a51853Cardnames ; "|51853|CardNames|Ten Of Clubs" .data:00000001000B6B58 dq offset a46368Cardnames ; "|46368|CardNames|Jack Of Clubs" .data:00000001000B6B60 dq offset a61344Cardnames ; "|61344|CardNames|Queen Of Clubs" .data:00000001000B6B68 dq offset a65017Cardnames ; "|65017|CardNames|King Of Clubs" .data:00000001000B6B70 dq offset a57807Cardnames ; "|57807|CardNames|Ace Of Clubs" .data:00000001000B6B78 dq offset a48455Cardnames ; "|48455|CardNames|Two Of Diamonds" .data:00000001000B6B80 dq offset a44156Cardnames ; "|44156|CardNames|Three Of Diamonds" .data:00000001000B6B88 dq offset a51672Cardnames ; "|51672|CardNames|Four Of Diamonds" .data:00000001000B6B90 dq offset a45972Cardnames ; "|45972|CardNames|Five Of Diamonds" .data:00000001000B6B98 dq offset a47206Cardnames ; "|47206|CardNames|Six Of Diamonds" .data:00000001000B6BA0 dq offset a48399Cardnames ; "|48399|CardNames|Seven Of Diamonds" .data:00000001000B6BA8 dq offset a47847Cardnames ; "|47847|CardNames|Eight Of Diamonds" .data:00000001000B6BB0 dq offset a48606Cardnames ; "|48606|CardNames|Nine Of Diamonds" .data:00000001000B6BB8 dq offset a61278Cardnames ; "|61278|CardNames|Ten Of Diamonds" .data:00000001000B6BC0 dq offset a52038Cardnames ; "|52038|CardNames|Jack Of Diamonds" .data:00000001000B6BC8 dq offset a54643Cardnames ; "|54643|CardNames|Queen Of Diamonds" .data:00000001000B6BD0 dq offset a48902Cardnames ; "|48902|CardNames|King Of Diamonds" .data:00000001000B6BD8 dq offset a46672Cardnames ; "|46672|CardNames|Ace Of Diamonds" .data:00000001000B6BE0 dq offset a41049Cardnames ; "|41049|CardNames|Two Of Spades" .data:00000001000B6BE8 dq offset a49327Cardnames ; "|49327|CardNames|Three Of Spades" .data:00000001000B6BF0 dq offset a51933Cardnames ; "|51933|CardNames|Four Of Spades" .data:00000001000B6BF8 dq offset a42651Cardnames ; "|42651|CardNames|Five Of Spades" .data:00000001000B6C00 dq offset a65342Cardnames ; "|65342|CardNames|Six Of Spades" .data:00000001000B6C08 dq offset a53644Cardnames ; "|53644|CardNames|Seven Of Spades" .data:00000001000B6C10 dq offset a54466Cardnames ; "|54466|CardNames|Eight Of Spades" .data:00000001000B6C18 dq offset a56874Cardnames ; "|56874|CardNames|Nine Of Spades" .data:00000001000B6C20 dq offset a46756Cardnames ; "|46756|CardNames|Ten Of Spades" .data:00000001000B6C28 dq offset a62876Cardnames ; "|62876|CardNames|Jack Of Spades" .data:00000001000B6C30 dq offset a64633Cardnames ; "|64633|CardNames|Queen Of Spades" .data:00000001000B6C38 dq offset a46215Cardnames ; "|46215|CardNames|King Of Spades" .data:00000001000B6C40 dq offset a60450Cardnames ; "|60450|CardNames|Ace Of Spades" .data:00000001000B6C48 dq offset a51010Cardnames ; "|51010|CardNames|Two Of Hearts" .data:00000001000B6C50 dq offset a64948Cardnames ; "|64948|CardNames|Three Of Hearts" .data:00000001000B6C58 dq offset a43079Cardnames ; "|43079|CardNames|Four Of Hearts" .data:00000001000B6C60 dq offset a57131Cardnames ; "|57131|CardNames|Five Of Hearts" .data:00000001000B6C68 dq offset a58953Cardnames ; "|58953|CardNames|Six Of Hearts" .data:00000001000B6C70 dq offset a45105Cardnames ; "|45105|CardNames|Seven Of Hearts" .data:00000001000B6C78 dq offset a47775Cardnames ; "|47775|CardNames|Eight Of Hearts" .data:00000001000B6C80 dq offset a41825Cardnames ; "|41825|CardNames|Nine Of Hearts" .data:00000001000B6C88 dq offset a41501Cardnames ; "|41501|CardNames|Ten Of Hearts" .data:00000001000B6C90 dq offset a47108Cardnames ; "|47108|CardNames|Jack Of Hearts" .data:00000001000B6C98 dq offset a55659Cardnames ; "|55659|CardNames|Queen Of Hearts" .data:00000001000B6CA0 dq offset a44572Cardnames ; "|44572|CardNames|King Of Hearts" .data:00000001000B6CA8 dq offset a44183Cardnames ; "|44183|CardNames|Ace Of Hearts"
If you want to do this to someone, be sure his/her mental health is stable.
Aside of function names from PDB file, there are lots of Log() function calls that can help significantly, because the Solitaire game reports about what it's doing right now.
Homework: try to "remove" several cards or two of clubs. And what if to swap card names in arrays of strings?
I also tried to pass a numbers like 0, 0..50 to Card:Init() (so to have 2 zeroes in a list of 52 numbers). Then I saw two "two of clubs" cards at one moment, but Solitaire behaves erratically.
This is patched Windows 7 Solitare: https://yurichev.com/blog/solitaire/Solitaire51.exe.