TAILIEUCHUNG - Cracker Handbook 1.0 part 55

Tham khảo tài liệu 'cracker handbook part 55', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | the destiny addressed by DI. Syntax MOVS This command does not need parameters since it takes as source address the content of the SI register and as destination the content of DI. The following sequence of instructions illustrates this MOV SI OFFSET VAR1 MOV DI OFFSET VAR2 MOVS First we initialize the values of SI and DI with the addresses of the VAR1 and VAR2 variables respectively then after executing MOVS the content of VAR1 is copied onto VAR2. The MOVSB and MOVSW are used in the same way as MOVS the first one moves one byte and the second one moves a word. Loading instructions They are specific register instructions. They are used to load bytes or chains of bytes onto a register. LODS LODSB LODSW LAHF LDS LEA LES LODS LODSB LODSW INSTRUCTION Purpose To load chains of a byte or a word into the accumulator. Syntax LODS This instruction takes the chain found on the address specified by SI loads it to the AL or AX register and adds or subtracts depending on the state of DF to SI if it is a bytes transfer or if it is a words transfer. MOV SI OFFSET VAR1 LODS The first line loads the VAR1 address on SI and the second line takes the content of that locality to the AL register. The LODSB and LODSW commands are used in the same way the first one loads a byte and the second one a word it uses the complete AX register . LAHF INSTRUCTION Purpose It transfers the content of the flags to the AH register. Syntax LAHF This instruction is useful to verify the state of the flags during the execution of our program. The flags are left in the following order inside the register SF ZF AF PF CF LDS INSTRUCTION Purpose To load the register of the data segment Syntax LDS destiny source The source operator must be a double word in memory. The word associated with the largest address is transferred to DS in other words it is taken as the segment address. The word associated with the smaller address is the displacement address and it is deposited in the register indicated as .

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