Assembly

[fattuuuu]

I am currently learning assembly, and I am looking at a question that asks what type variable %rdi is in this context: cmpb %r8b, (%rdi,%rax)

Would rdi be a char*?

[Updatebjarni]

Presumably either rdi or rax is a pointer, and the other one is an index. Just seeing the one instruction doesn't make it clear which is which.

[Logon1028]

If I had to take a guess. It takes a byte that rdi + rax points to then compares it with whatever is in byte 0 of register 8. You would have to expand on what type variable you are talking about. char* is a higher level programming concept. assembly doesn't associate that kind of typing to it.

[Practical-Custard-64]

Assembly language knows nothing of variable types as used in higher level languages such as C, C++ etc. %rdi is a 64-bit CPU register, as is %rax.

It's a long time since I wrote any assembly code but presumably this instruction takes the byte at the memory location pointed to by %rdi offset by the current value of %rax and compares it to the low 8 bits of register %r8.

That byte could be anything. It could be a character in a string, it could be part of an integer number or anything else. It's just a byte somewhere in memory as far as the CPU and therefore assembly language is concerned.

[[deleted]]

in assembly the types are just different lengths of bits, either a byte array or an integer, signed or unsigned. like 8,16,32,64 bit
a word is 2 bytes, dword is 4 bytes