x86

问题 Jump's based on comparing signed integers use the Zero, Sign, and Overflow flag to determine the relationship between operands. After CMP with two signed operands, there are three possible scenario's: ZF = 1 - Destination = Source SF = OF - Destination > Source SF != OF - Destination < Source I'm having trouble understanding scenario 2 and 3. I've worked through the possible combinations and see that they do work - but I still can't figure out why they work. Can anyone explain why a

问题 i'm currently learning x86 assembly language and wondered what is the better way for implementing loops. One way would be to mov a value to ecx register and use the loop instruction and the other way would be using a jmp instruction and then comes the loop body and then a conditional jumping eventually to the beginning of the loop body. I guess the first one will has a better readability but other then that i don't know why to use it. 回答1: When you mention jmp+body+test, I believe you are

问题 i'm currently learning x86 assembly language and wondered what is the better way for implementing loops. One way would be to mov a value to ecx register and use the loop instruction and the other way would be using a jmp instruction and then comes the loop body and then a conditional jumping eventually to the beginning of the loop body. I guess the first one will has a better readability but other then that i don't know why to use it. 回答1: When you mention jmp+body+test, I believe you are

问题 i'm currently learning x86 assembly language and wondered what is the better way for implementing loops. One way would be to mov a value to ecx register and use the loop instruction and the other way would be using a jmp instruction and then comes the loop body and then a conditional jumping eventually to the beginning of the loop body. I guess the first one will has a better readability but other then that i don't know why to use it. 回答1: When you mention jmp+body+test, I believe you are

问题 i'm currently learning x86 assembly language and wondered what is the better way for implementing loops. One way would be to mov a value to ecx register and use the loop instruction and the other way would be using a jmp instruction and then comes the loop body and then a conditional jumping eventually to the beginning of the loop body. I guess the first one will has a better readability but other then that i don't know why to use it. 回答1: When you mention jmp+body+test, I believe you are

问题 i'm currently learning x86 assembly language and wondered what is the better way for implementing loops. One way would be to mov a value to ecx register and use the loop instruction and the other way would be using a jmp instruction and then comes the loop body and then a conditional jumping eventually to the beginning of the loop body. I guess the first one will has a better readability but other then that i don't know why to use it. 回答1: When you mention jmp+body+test, I believe you are

问题 Does the LEA instruction support negative displacement? mov rax, 1 lea rsi, [rsp - rax] When I use the above code in my asm file I got the error: $ nasm -f macho64 test.asm $ error: invalid effective address I Know that we can do pointer arithmetic like this in C: void foo(char *a, size_t b) { *(a - b) = 1; } then I assume that: lea rsi, [rsp - rax] will work. And I also try to see what the GCC compiler do by using: $ gcc -S foo.c // foo.c has the function foo(above) in it but my asm

问题 Does the LEA instruction support negative displacement? mov rax, 1 lea rsi, [rsp - rax] When I use the above code in my asm file I got the error: $ nasm -f macho64 test.asm $ error: invalid effective address I Know that we can do pointer arithmetic like this in C: void foo(char *a, size_t b) { *(a - b) = 1; } then I assume that: lea rsi, [rsp - rax] will work. And I also try to see what the GCC compiler do by using: $ gcc -S foo.c // foo.c has the function foo(above) in it but my asm

问题 Does the LEA instruction support negative displacement? mov rax, 1 lea rsi, [rsp - rax] When I use the above code in my asm file I got the error: $ nasm -f macho64 test.asm $ error: invalid effective address I Know that we can do pointer arithmetic like this in C: void foo(char *a, size_t b) { *(a - b) = 1; } then I assume that: lea rsi, [rsp - rax] will work. And I also try to see what the GCC compiler do by using: $ gcc -S foo.c // foo.c has the function foo(above) in it but my asm

问题 Does the LEA instruction support negative displacement? mov rax, 1 lea rsi, [rsp - rax] When I use the above code in my asm file I got the error: $ nasm -f macho64 test.asm $ error: invalid effective address I Know that we can do pointer arithmetic like this in C: void foo(char *a, size_t b) { *(a - b) = 1; } then I assume that: lea rsi, [rsp - rax] will work. And I also try to see what the GCC compiler do by using: $ gcc -S foo.c // foo.c has the function foo(above) in it but my asm