assembly

问题 i have an assignment that asks to define 4 integers, each of a different byte length (1, 2, 4, 8) would this code work? segment .data one db 1 two dw 01 four dd 1011 eight dq 01101110 global _start _start: mov rax, [one] ; mov rbx, [two] ; im also curious if i can safely store these values into registers to be used for addition in the future. I'm supposed to use sign extension for the shorter values, but could use some direction 回答1: You're writing constants in decimal. If you want the digits

问题 Let's say there is a piece of code: mov al, 12 mov bl, 4 sub al, bl In this case, the CF = 0 flag, but in my opinion it should be equal to 1, since the subtraction operation is implemented on an addition operation and the processor does not know what we are giving it as input, be it signed or unsigned numbers, it just does its job. That is, the code above is equivalent to the following: Enter the value 12 into the al register, i.e. 0000 1100 Enter the value 4 into the bl register, i.e. 0000

问题 Let's say there is a piece of code: mov al, 12 mov bl, 4 sub al, bl In this case, the CF = 0 flag, but in my opinion it should be equal to 1, since the subtraction operation is implemented on an addition operation and the processor does not know what we are giving it as input, be it signed or unsigned numbers, it just does its job. That is, the code above is equivalent to the following: Enter the value 12 into the al register, i.e. 0000 1100 Enter the value 4 into the bl register, i.e. 0000

问题 Let's say there is a piece of code: mov al, 12 mov bl, 4 sub al, bl In this case, the CF = 0 flag, but in my opinion it should be equal to 1, since the subtraction operation is implemented on an addition operation and the processor does not know what we are giving it as input, be it signed or unsigned numbers, it just does its job. That is, the code above is equivalent to the following: Enter the value 12 into the al register, i.e. 0000 1100 Enter the value 4 into the bl register, i.e. 0000

问题 Let's say there is a piece of code: mov al, 12 mov bl, 4 sub al, bl In this case, the CF = 0 flag, but in my opinion it should be equal to 1, since the subtraction operation is implemented on an addition operation and the processor does not know what we are giving it as input, be it signed or unsigned numbers, it just does its job. That is, the code above is equivalent to the following: Enter the value 12 into the al register, i.e. 0000 1100 Enter the value 4 into the bl register, i.e. 0000

问题 Let's say there is a piece of code: mov al, 12 mov bl, 4 sub al, bl In this case, the CF = 0 flag, but in my opinion it should be equal to 1, since the subtraction operation is implemented on an addition operation and the processor does not know what we are giving it as input, be it signed or unsigned numbers, it just does its job. That is, the code above is equivalent to the following: Enter the value 12 into the al register, i.e. 0000 1100 Enter the value 4 into the bl register, i.e. 0000

问题 Let's say there is a piece of code: mov al, 12 mov bl, 4 sub al, bl In this case, the CF = 0 flag, but in my opinion it should be equal to 1, since the subtraction operation is implemented on an addition operation and the processor does not know what we are giving it as input, be it signed or unsigned numbers, it just does its job. That is, the code above is equivalent to the following: Enter the value 12 into the al register, i.e. 0000 1100 Enter the value 4 into the bl register, i.e. 0000

问题 Why does al contain the number of vector parameters in assembly? Why are vector parameters any different from normal parameters for the callee? 回答1: The value is used for optimization as stated in the ABI document The prologue should use %al to avoid unnecessarily saving XMM registers. This is especially important for integer only programs to prevent the initialization of the XMM unit. 3.5.7 Variable Argument Lists - The Register Save Area. System V Application Binary Interface version 1.0

问题 Why does al contain the number of vector parameters in assembly? Why are vector parameters any different from normal parameters for the callee? 回答1: The value is used for optimization as stated in the ABI document The prologue should use %al to avoid unnecessarily saving XMM registers. This is especially important for integer only programs to prevent the initialization of the XMM unit. 3.5.7 Variable Argument Lists - The Register Save Area. System V Application Binary Interface version 1.0

问题 Why does al contain the number of vector parameters in assembly? Why are vector parameters any different from normal parameters for the callee? 回答1: The value is used for optimization as stated in the ABI document The prologue should use %al to avoid unnecessarily saving XMM registers. This is especially important for integer only programs to prevent the initialization of the XMM unit. 3.5.7 Variable Argument Lists - The Register Save Area. System V Application Binary Interface version 1.0