Preliminare

AT&T vs Intel sytax

And again about memory reference

ALL

The propose syntax is:

        __asm__ __volatile__ (
		"statement" : "output_regs" (passed_var_from_c_code) : "input_regs" (passed_var_from_c_code) : "clobbered_regs"
	);

And here are the list of registers and the symbols:

        a	: e(a)x
	b	: e(b)x
	c	: e(c)x
	d	: e(d)x
	S	: e(S)i
	D	: e(D)i

	i	: (i)mmediate that would allow an address known only at link time
	I	: (I)mmediate 0 to 31
	J	: immediate 0 to 63
	K	: immediate 255
	L	: immediate 65535
	M	: immediate 0 to 3 (shift that can be done with lea)
	N	: immediate 0 to 255 (one-byte immediate value)
	O	: immediate 0 to 32
	
	q	: byte-addressable register or dynamically allocated register from eax, ebx, ecx, and edx
	r	: (r)egister same as q but also consider esi and edi
	g	: (g)eneral effective address register eax, ebx, ecx, edx, or variable in memory
	m	: (m)emory effective address
	A	: eax and edx combined into 64-bit integer (for long longs type)

Some sample descriptive usage:

      1. Using dynamically allocated register
        long int	a, b;

	a = 1; b = 2;
        __asm__ __volatile__ (
		"movl %1, %0" : "=r" (b) : "rI" (a)
	);

	or 

        __asm__ __volatile__ (
		"movl %0, %0" : "=r" (b) : "0" (a)
	);

	Note:
	  - Above code will operate in similiar way as b = a.
	  - The "rI" from first code meas a could use r or I register.
	  - The "0" from second code make %0 = %1, so need not use %1 because %1 is the same as %0, this need some explanation.
	    we see this code:
	    	movl %1, %0	means %1 as source and %0 as destination.
	    when we use:
	    	movl %0, %0	means the first %0 is source and the later %0 is destination.
	    from above, the input is a and output is b.
	    then the %0 will be interpreted as:
	    	a	: when act as input or source
	    	b	: when act as output or destination
	    
	    Q : Is it legal of using the same register for one instruction simultaneously ? 
	    A : well actually gcc use temporary register to do that
      
      2. Clobbered exmaple
        __asm__ __volatile__ (
		"movl %0, $1" : : "r" (a) : "r0"
	);		
	
      3. The very special cases like K are mostly used inside GCC in alternative code sequences,
         providing a special-case way to do something like ANDing with 255.
	 
      4. Using I
         For x86 rotate left

	 __asm__ __volatile__ (
	 	"roll %1, %0" : "=g" (result) : "cI" (rotate), "0" (input)
	 )

The constraint

well see the gcc doc about constraint, AKU MALES...

Some basic that i often forget

        -- JMP INSTRUCTION
	Purpose	: Unconditional jump.
	Syntax	:
		JMP destiny
	Note	:
		This instruction is used to deviate the flow of a program without taking into account the actual conditions of the flags or of the data.
	
	-- JA (JNBE) INSTRUCTION
	Purpose	: Conditional jump.
	Syntax	:
		JA Label
	Note	:
		After a comparison this command jumps if it is or jumps if it is not down or if not it is the equal.
		This means that the jump is only done if the CF flag is deactivated or if the ZF flag is deactivated, that is that one of the two be equal to zero.
	
	-- JAE (JNB) INSTRUCTION
	Purpose	: Conditional jump.
	Syntax	:
		JAE label
	Note	:
		It jumps if it is or it is the equal or if it is not down.
		The jump is done if CF is deactivated.

	-- JB (JNAE) INSTRUCTION
	Purpose	: Conditional jump.
	Syntax	:
		JB label
	Note	:
		It jumps if it is down, if it is not , or if it is the equal.
		The jump is done if CF is activated.

	-- JBE (JNA) INSTRUCTION
	Purpose	: Conditional jump.
	Syntax	:
		JBE label
	Note	:
		It jumps if it is down, the equal, or if it is not .
		The jump is done if CF is activated or if ZF is activated, that any of them be equal to 1.

	-- JE (JZ) INSTRUCTION
	Purpose	: Conditional jump.
	Syntax	:
		JE label
	Note	:
		It jumps if it is the equal or if it is zero.
		The jump is done if ZF is activated.

	-- JNE (JNZ) INSTRUCTION
	Purpose	: Conditional jump.
	Syntax	:
		JNE label
	Note	:
		It jumps if it is not equal or zero.
		The jump will be done if ZF is deactivated.

	-- JG (JNLE) INSTRUCTION
	Purpose	: Conditional jump, and the sign is taken into account.
	Syntax	:
		JG label
	Note	:
		It jumps if it is larger, if it is not larger or equal.
		The jump occurs if ZF = 0 or if OF = SF.

	-- JGE (JNL) INSTRUCTION
	Purpose	: Conditional jump, and the sign is taken into account.
	Syntax	:
		JGE label
	Note	:
		It jumps if it is larger or less than, or equal to.
		The jump is done if SF = OF

	-- JL (JNGE) INSTRUCTION
	Purpose	: Conditional jump, and the sign is taken into account.
	Syntax	:
		JL label
	Note	:
		It jumps if it is less than or if it is not larger than or equal to.
		The jump is done if SF is different than OF.

	-- JLE (JNG) INSTRUCTION
	Purpose	: Conditional jump, and the sign is taken into account.
	Syntax	:
		JLE label
	Note	:
		It jumps if it is less than or equal to, or if it is not larger.
		The jump is done if ZF = 1 or if SF is defferent than OF.

	-- JC INSTRUCTION
	Purpose	: Conditional jump, and the flags are taken into account.
	Syntax	:
		JC label
	Note	:
		It jumps if there is cartage.
		The jump is done if CF = 1

	-- JNC INSTRUCTION
	Purpose	: Conditional jump, and the state of the flags is taken into account.
	Syntax	:
		NC label
	Note	:
		It jumps if there is no cartage.
		The jump is done if CF = 0.

	-- JNO INSTRUCTION
	Purpose	: Conditional jump, and the state of the flags is taken into account.
	Syntax	:
		JNO label
	Note	:
		It jumps if there is no overflow.
		The jump is done if OF = 0.

	-- JNP (JPO) INSTRUCTION
	Purpose	: Conditional jump, and the state of the flags is taken into account.
	Syntax	:
		JNP label
	Note	:
		It jumps if there is no parity or if the parity is uneven.
		The jump is done if PF = 0.

	-- JNS INSTRUCTION
	Purpose	: Conditional jump, and the state of the flags is taken into account.
	Syntax	:
		JNP label
	Note	:
		It jumps if the sign is deactivated.
		The jump is done if SF = 0.

	-- JO INSTRUCTION
	Purpose	: Conditional jump, and the state of the flags is taken into account.
	Syntax	:
		JO label
	Note	:
		It jumps if there is overflow.
		The jump is done if OF = 1.

	-- JP (JPE) INSTRUCTION
	Purpose	: Conditional jump, the state of the flags is taken into account.
	Syntax	:
		JP label
	Note	:
		It jumps if there is parity or if the parity is even.
		The jump is done if PF = 1.

	-- JS INSTRUCTION
	Purpose	: Conditional jump, and the state of the flags is taken into account.
	Syntax	:
		JS label
	Note	:
		It jumps if the sign is on.
		The jump is done if SF = 1.

- d