Script Container

YSC files contain GTA V's game scripts. The new format is an adaptation of the script container format used in Red Dead Redemption.

File Format

The basic format of YSC starts with a header that's 0x80 bytes in size, there are still some unknowns in the header but for basic dissassembling you have enough information.

struct YSCHeader
{
	QWORD pageBase;// 0x00
	QWORD pageMapPointer;// 0x08
	QWORD CodeBlocksBasePointer;// 0x10 Points to an array of code block offsets
	DWORD GlobalsSignature;// 0x18
	DWORD CodeSize;// 0x1C - The size of all the code tables
	DWORD ParameterCount;// 0x20 - These are for starting a script with args. The args appear at the start of the script static variables
	DWORD StaticCount;// 0x24 - The number of static variables in the script
	DWORD GlobalCount;// 0x28 - This is used for scripts that seem to initialise global variable tables
	DWORD NativesCount;// 0x2C - The total amount of natives in the native table
	QWORD StaticsPointer;// 0x30 - The Offset in file where static variables are initialised
	QWORD GlobalsPointer;// 0x38 - The Offset in file where global variales are initilaised(only used for registration scripts)
	QWORD NativesPointer;// 0x40 - The Offset in file where the natives table is stored
	QWORD Null1;//0x48
	QWORD Null2;//0x50;
	DWORD ScriptNameHash;//0x58 - A Jenkins hash of the scripts name
	DWORD UnkUsually1;//0x5C
	QWORD ScriptNamePointer;//0x60 - Points to an offset in the file that has the name of the script
	QWORD StringBlocksBasePointer;//0x68 - Points to an array of string block offsets
	DWORD StringSize;//0x70 - The Size of all the string tables
	DWORD Null3;//0x74
	DWORD Null4;//0x78
	DWORD Null4;//0x7C
};

All Pointer items are stored in the file as 0x50XXXXXX and must therefore be masked with 0xFFFFFF to get their actual file offset.

Pages

The Code and Strings used by the script are stored in pages, each one up to a maximum size of 0x4000 bytes. The number of pages used can be calculated based of the CodeSize/StringSize using this:

int pageCount = (totalSize + 0x3FFF) >> 14;

The size of each of the pages can be calculated using this function

int pageSize(int pageIndex, int totalSize)
{
	if (pageIndex > (totalSize >> 14) || pageIndex < 0){//page out of range
		return 0;
	}else if (pageIndex == (totalSize >> 14)){
		return totalSize & 0x3FFF;
	}
	return 0x4000;
}

Code

The Poistion of each of the code pages can be found by reading the positions stored in the array pointer to from CodeBlocksBasePointer, then you can read up to pageSize in that page. The code itself is a set of 127 opcodes that is ran on a stack machine.

Opcodes

ID	Name	Description	Length
0	nop	No operation	1 byte
1	iadd	Adds the top 2 items on the stack	1 byte
2	isub	Subtracts the top 2 items on the stack	1 byte
3	imul	Multiplies the top 2 items on the stack	1 byte
4	idiv	Divides the top 2 items on the stack	1 byte
5	imod	Mods the top 2 items on the stack	1 byte
6	iszero	Checks the first item on the stack to see if it equals 0	1 byte
7	ineg	Reverses the sign on the item on the top of the stack	1 byte
8	icmpeq	Compares the top 2 integers on the stack to see if they are equal	1 byte
9	icmpne	Compares the top 2 integers on the stack to see if they are not equal	1 byte
10	icmpgt	Compares the top 2 integers on the stack to see if the first one is greater than the second one	1 byte
11	icmpge	Compares the top 2 integers on the stack to see if the first one is greater than or equal to the second one	1 byte
12	icmplt	Compares the top 2 integers on the stack to see if the first one is less than the second one	1 byte
13	icmple	Compares the top 2 integers on the stack to see if the first one is less than or equal to the second one	1 byte
14	fadd	Adds the top 2 floats on the stack	1 byte
15	fsub	Subtracts the top 2 floats on the stack	1 byte
16	fmul	Multiplies the top 2 floats on the stack	1 byte
17	fdiv	Divides the top 2 floats on the stack	1 byte
18	fmod	Mods the top 2 floats on the stack	1 byte
19	fneg	Reverses the sign on the first float on the stack	1 byte
20	fcmpeq	Compares the top 2 floats on the stack to see if they are equal	1 byte
21	fcmpne	Compares the top 2 floats on the stack to see if they are not equal	1 byte
22	fcmpgt	Compares the top 2 floats on the stack to see if the first one is greater than the second one	1 byte
23	fcmpge	Compares the top 2 floats on the stack to see if the first one is greater than or equal to the second one	1 byte
24	fcmplt	Compares the top 2 floats on the stack to see if the first one is less than the second one	1 byte
25	fcmple	Compares the top 2 floats on the stack to see if the first one is less than or equal to the second one	1 byte
26	vadd	Adds the top 2 Vectors[1] on the stack	1 byte
27	vsub	Subtracts the top 2 Vectors[1] on the stack	1 byte
28	vmul	Multiplies the top 2 Vectors[1] on the stack	1 byte
29	vdiv	Divides the top 2 Vectors[1] on the stack	1 byte
30	vneg	Reverses the sign on the first vector[1] on the stack	1 byte
31	iand	Performs an And operation to the first 2 integers on the stack	1 byte
32	ior	Performs an Or operation to the first 2 integers on the stack	1 byte
33	ixor	Performs a Xor operation to the first 2 integers on the stack	1 byte
34	itof	Converts the top integer on the stack to a float, and puts that float on the stack	1 byte
35	ftoi	Converts the top float on the stack to an integer, and puts that integer on the stack	1 byte
36	ftov	Converts the top float into a Vector containing 3 instances of the same float, and pushes the pointer to that Vector onto the top of the stack	1 byte
37	pushb	Pushes a byte onto the stack, the byte is defined as the next byte after the opcode	2 bytes
38	pushb2	Pushes 2 bytes onto the stack, the bytes are the next 2 bytes after the opcode	3 bytes
39	pushb3	Pushes 3 bytes onto the stack, the bytes are the next 3 bytes after the opcode	4 bytes
40	push	Pushes an int onto the stack, the integer is defined in the next 4 bytes after the opcode	5 bytes
41	pushf	Pushes a float onto the stack, the float is defined in the next 4 bytes after the opcode	5 bytes
42	dup	Duplicates the first item on the stack, and pushes it back onto the stack	1 byte
43	pop	Pops the top item off the stack	1 byte
44	native	Calls a native function. The number of arguments for the native to take is defined in the first 6 bits of the next byte after the opcode(0-63). The number of returns is stored in the following 2 bits(0-3). The hash of the native functions is stored in the native table at the index specified by the following 2 bytes(expressed as an unsigned short)	4 bytes
45	enter	Indicates the beginning of an internal function. The byte after the opcode indicates the amount of arguments the function takes off the stack, and the next 2 bytes after that indicate the number of variables the function will have to generate on the stack. The following byte indicates how many bytes to skip past after the opcode(usually so a name can be appended to the function definition)	5 bytes + value of 5th byte
46	ret	Indicates the end of an internal function. The byte after the opcode indicates the amount of arguments that will have to be popped off the stack, and the next byte after that indicates the stack number of the return address	3 bytes
47	pget	Pops a pointer off the stack and pushes the value stored in that pointer back onto the stack	1 byte
48	pset	Pops 2 items off the stack and stores the second item at the location of the first item (the first item being a pointer)	1 byte
49	peekset	Pops the first item off the stack and peeks at the second item on the stack, then stores the first item at the location pointed to by the second item on the stack	1 byte
50	tostack	Pops 2 items off the stack, the first being the number of items, second being the memory address. It then pushes that many items to the stack from the memory address	1 byte
51	fromstack	Pops 2 items off the stack, the first being the number of items, second being the memory address. It then pops that many items from the stack to the memory address	1 byte
52	getarrayp1	Pops 2 items off the stack, the first being an array index, second being the pointer to an array. It then pushes the pointer to theindex in the array to the top of the stack. The size each item in the array is determined by the byte following the opcode	2 bytes
53	getarray1	Pops 2 items off the stack, the first being an array index, second being the pointer to an array. It then pushes the item at the array index to the top of the stack. The size each item in the array is determined by the byte following the opcode	2 bytes
54	setarray1	Pops 3 items off the stack, the first being the value to set, second being an array index and last being the pointer to an array. It the sets the value at the index in the array to first value. The size each item in the array is determined by the byte following the opcode	2 bytes
55	getframep1	Pushes the pointer to the frame variable at the index specified by the byte following the opcode	2 bytes
56	getframe1	Pushes the value of the frame variable at the index specified by the byte following the opcode	2 bytes
57	setframe1	Pops an item off the stack, then sets the frame variable at the index specified by the byte following the opcode to the item	2 bytes
58	getstaticp1	Pushes the pointer to the static variable at the index specified by the byte following the opcode	2 bytes
59	getstatic1	Pushes the value of the static variable at the index specified by the byte following the opcode	2 bytes
60	setstatic1	Pops an item off the stack, then sets the static variable at the index specified by the byte following the opcode to the item	2 bytes
61	addi	Adds the byte directly after the opcode to the integer value at the top of the stack, then pushes the new value to the top of the stack	2 bytes
62	multi	Multiplies the byte directly after the opcode to the integer value at the top of the stack, then pushes the new value to the top of the stack	2 bytes
63	stackgetimmp	Pops an index and a pointer to a struct off the stack, pushes the pointer to the item at 8 times the index in the struct	1 byte
64	getimmp1	Pops an pointer to a struct off the stack, pushes the pointer to the item at the index specified by 8 times the byte following the opcode	2 bytes
65	getimm1	Pops an pointer to a struct off the stack, pushes the value of the item at the index specified by 8 times the byte following the opcode	2 bytes
66	setimm1	Pops an value and a pointer to a struct off the stack, sets the item at the index specified by 8 times the byte following the opcode to the value popped of the stack	2 bytes
67	pushshort	Pushes a signed short to the stack, the value is the 2 bytes following the opcode	3 bytes
68	addi2	Adds the short directly after the opcode to the integer value at the top of the stack, then pushes the new value to the top of the stack	3 bytes
69	multi2	Multiplies the short directly after the opcode to the integer value at the top of the stack, then pushes the new value to the top of the stack	3 bytes
70	getimmp2	Pops an pointer to a struct off the stack, pushes the pointer to the item at the index specified by 8 times the 2 bytes following the opcode	3 bytes
71	getimm2	Pops an pointer to a struct off the stack, pushes the value of the item at the index specified by 8 times the 2 bytes following the opcode	3 bytes
72	setimm2	Pops an value and a pointer to a struct off the stack, sets the item at the index specified by 8 times the 2 bytes following the opcode to the value popped of the stack	3 bytes
73	getarrayp2	Pops 2 items off the stack, the first being an array index, second being the pointer to an array. It then pushes the pointer to theindex in the array to the top of the stack. The size each item in the array is determined by the 2 bytes following the opcode	3 bytes
74	getarray2	Pops 2 items off the stack, the first being an array index, second being the pointer to an array. It then pushes the item at the array index to the top of the stack. The size each item in the array is determined by the 2 bytes following the opcode	3 bytes
75	setarray2	Pops 3 items off the stack, the first being the value to set, second being an array index and last being the pointer to an array. It the sets the value at the index in the array to first value. The size each item in the array is determined by the 2 bytes following the opcode	3 bytes
76	getframep2	Pushes the pointer to the frame variable at the index specified by the 2 bytes following the opcode	3 bytes
77	getframe2	Pushes the value of the frame variable at the index specified by the 2 bytes following the opcode	3 bytes
78	setframe2	Pops an item off the stack, then sets the frame variable at the index specified by the 2 bytes following the opcode to the item	3 bytes
79	getstaticp2	Pushes the pointer to the static variable at the index specified by the 2 bytes following the opcode	3 bytes
80	getstatic2	Pushes the value of the static variable at the index specified by the 2 bytes following the opcode	3 bytes
81	setstatic2	Pops an item off the stack, then sets the static variable at the index specified by the 2 bytes following the opcode to the item	3 bytes
82	getglobalp2	Pushes the pointer to the global variable at the index specified by the 2 bytes following the opcode	3 bytes
83	getglobal2	Pushes the value of the global variable at the index specified by the 2 bytes following the opcode	3 bytes
84	setglobal2	Pops an item off the stack, then sets the global variable at the index specified by the 2 bytes following the opcode to the item	3 bytes
85	b	Performs a relative jump to a new location in the code, the relative offset is the signed short following the opcode	3 bytes
86	bz	Performs a relative jump to a new location in the code if the item at the top of the stack is zero, the relative offset is the signed short following the opcode	3 bytes
87	bne	Pops 2 items off the stack, Performs an integer comparison on them and performs a relative jump to a new location in the code if the first is not equal to the second. The relative offset is the signed short following the opcode	3 bytes
88	beq	Pops 2 items off the stack, Performs an integer comparison on them and performs a relative jump to a new location in the code if the first is equal to the second. The relative offset is the signed short following the opcode	3 bytes
89	ble	Pops 2 items off the stack, Performs an integer comparison on them and performs a relative jump to a new location in the code if the first is less than or equal to the second. The relative offset is the signed short following the opcode	3 bytes
90	blt	Pops 2 items off the stack, Performs an integer comparison on them and performs a relative jump to a new location in the code if the first is less than the second. The relative offset is the signed short following the opcode	3 bytes
91	bge	Pops 2 items off the stack, Performs an integer comparison on them and performs a relative jump to a new location in the code if the first is greater than or equal to the second. The relative offset is the signed short following the opcode	3 bytes
92	bgt	Pops 2 items off the stack, Performs an integer comparison on them and performs a relative jump to a new location in the code if the first is greater than the second. The relative offset is the signed short following the opcode	3 bytes
93	call	Calls a function within the script, and puts the return address on top of the stack. The location of the function is defined in the next 3 bytes after the opcode	4 bytes
94	getglobalp3	Pushes the pointer to the global variable at the index specified by the 3 bytes following the opcode	4 bytes
95	getglobal3	Pushes the value of the global variable at the index specified by the 3 bytes following the opcode	4 bytes
96	setglobal3	Pops an item off the stack, then sets the global variable at the index specified by the 3 bytes following the opcode to the item	4 bytes
97	pushi24	Pushes an unsigned 24 bit integer to the stack, the value is the 3 bytes following the opcode	4 bytes
98	switch	Pops the item to compare off the stack, and then jumps to location corresponding to that item. After the opcode byte it contains a byte defining the number of possible entries, and after that the number of possible entries times 6 are taken up with repeating instances of 4 bytes of the index identifier, and 2 bytes of the relative jump offset to jump to if that index is correct (note jump offset is unsigned unlike branch instructions)	(Byte after opcode * 6) + 2 bytes
99	pushstring	Pops an integer off the stack, then returns the pointer to the string stored at that index in the String Table	1 byte
100	gethash	Pops the pointer to a string off the stack. The computes a jenkins-one-at-a-time hash on the string and pushes the result to the stack	1 byte
101	strncpy	Pops a pointer to a destination buffer and a string, copies the string to the destination buffer. The size of the buffer is specified in the byte following the opcode	2 bytes
102	itos	Pops a pointer to a destination buffer and a integer, converts the integer to a string and stores it in the destination buffer. The size of the buffer is specified in the byte following the opcode	2 bytes
103	strncat	Pops a pointer to a destination buffer and a string, appends the string to the string in the destination buffer. The size of the buffer is specified in the byte following the opcode	2 bytes
104	strncatint	Pops a pointer to a destination buffer and a integer, converts the integer to a string and appends it to the string in the destination buffer. The size of the buffer is specified in the byte following the opcode	2 bytes
105	memcpy	Pops 3 items off the stack. Copies the third item's memory into the first item's memory with repeating defined by the second item. It then appends a null terminator to the first item's memory	1 byte
106	catch	Sets up a safe area that has the ability to catch errors - not used in release builds of GTA	1 byte
107	throw	Indicates an area that handles a script error relative to the catch opcode - not used in release builds of GTA	1 byte
108	pCall	Calls a function within the script, and puts the return address on top of the stack. The location of the function is defined in the integer at the top of the stack	1 byte
109	pushn1	Pushes the integer -1 to the top of the stack	1 byte
110	push0	Pushes the integer 0 to the top of the stack	1 byte
111	push1	Pushes the integer 1 to the top of the stack	1 byte
112	push2	Pushes the integer 2 to the top of the stack	1 byte
113	push3	Pushes the integer 3 to the top of the stack	1 byte
114	push4	Pushes the integer 4 to the top of the stack	1 byte
115	push5	Pushes the integer 5 to the top of the stack	1 byte
116	push6	Pushes the integer 6 to the top of the stack	1 byte
117	push7	Pushes the integer 7 to the top of the stack	1 byte
118	pushfn1	Pushes the float -1.0 to the top of the stack	1 byte
119	pushf0	Pushes the float 0.0 to the top of the stack	1 byte
120	pushf1	Pushes the float 1.0 to the top of the stack	1 byte
121	pushf2	Pushes the float 2.0 to the top of the stack	1 byte
122	pushf3	Pushes the float 3.0 to the top of the stack	1 byte
123	pushf4	Pushes the float 4.0 to the top of the stack	1 byte
124	pushf5	Pushes the float 5.0 to the top of the stack	1 byte
125	pushf6	Pushes the float 6.0 to the top of the stack	1 byte
126	pushf7	Pushes the float 7.0 to the top of the stack	1 byte

Native Functions

All Natives used by the script are stored in a table of hashes (seemingly random unlike on X360/PS3 versions where they were a jenkins hash of the native name). The address of the table and size can be read from the YSC Header. The native hashes are rotated right by the size of the codeSize + the index of the native in the table. To get the hash of a native from a native table index use this. The nativeTable can be got from reading the pointer from the header and masking it with 0xFFFFFF. Then returning that position in the YSC File.

QWORD getNativeHash(WORD index, const QWORD* nativeTable, DWORD codeSize)
{
	BYTE rotate = (index + codeSize) & 0x3F;
	return nativeTable[index] << rotate | nativeTable[index] >> (64 - rotate);
}

Since game version b350. Rockstar began changing the hashes of the natives each game update. Its unsure if they are random or not, but either way trying to disassemble scripts in patch b350 or later will require translating all hashes from the nativeTable(after rotating them) into their vanilla game hash. This can be done using the translation tables Alexander Blade provides in here:  GTAForums: Script/Native Documentation