x86-64

问题 Why is it that 32-bit C pushes all function arguments straight onto the stack while 64-bit C puts the first 6 arguments into registers and the rest on the stack? So the 32-bit stack would look like: ... arg2 arg1 return address old %rbp While the 64-bit stack would look like: ... arg8 arg7 return address old %rbp arg6 arg5 arg4 arg3 arg2 arg1 So why does 64-bit C do this? Isn't it much easier to just push everything to the stack instead of put the first 6 arguments in registers just to move

问题 I often forget the registers that I need to use for each argument in a syscall, and everytime I forget I just visit this question. The right order for integer/pointer args to x86_64 user-space function calls is: %rdi , %rsi , %rdx , %rcx , %r8 and %r9 . (with variadic functions taking AL = the number of FP args, up to 8) Or for system calls, %rax (syscall call number), and same args except %r10 instead of %rcx . What's the best way to remember these registers instead of google this question

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

来源： https://stackoverflow.com/questions/50571275/why-does-a-syscall-clobber-rcx-and-r11

来源： https://stackoverflow.com/questions/29668332/what-is-happening-in-this-assembly-code

来源： https://stackoverflow.com/questions/29668332/what-is-happening-in-this-assembly-code

来源： https://stackoverflow.com/questions/64729055/what-does-aligning-the-stack-mean-in-assembly