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→Registers
[[Category:Assembly Language]]
This page contains very basic information on the x86_64 architecture: the [[Register|register]] layout and naming and the some basic instructions.
== Registers ==
Usage during [[Syscalls|syscall]]/function call:
* First six arguments are in rdi, rsi, rdx, rcx, r8d, r9d; remaining arguments are on the stack.
* For syscalls, the syscall number is in rax. For procedure calls, rax should be set to 0.
* Return value is in rax.
* The called routine is expected to save preserve rsp,rbp, rbx, r12, r13, r14, and r15 but may trample any other registers.
=== Floating-Point and SIMD Registers ===
add %r10,%r11 // add r10 and r11, put result in r11
add $5,%r10 // add 5 to r10, put result in r10 call ''label'' // call a subroutine / function / procedure cmp %r10,%r11 // compare register r10 with register r11. The comparison sets flags in the processor status register which affect conditional jumps. cmp $99,%r11 // compare the number 99 with register r11. The comparison sets flags in the processor status register which affect conditional jumps. div $%r10 // divide rax by the given register (r10), places quotient into rax and remainder into rdx (rdx must be zero before this instruction)
inc %r10 // increment r10
jmp ''label'' // jump to label
jne ''label'' // jump to label if not equal
jl ''label'' // jump to label if less
mov %r10,(%r11) // move data from r10 to address pointed to by r11
mov (%r10),%r11 // move data from address pointed to by r10 to r10
mul $%r10 // multiplies rax by r10, places result in rax and overflow in rdx
push %r10 // push r10 onto the stack
pop %r10 // pop r10 off the stack
ret // routine from subroutine (counterpart to call)
syscall // invoke a syscall (in 32-bit mode, use "int $0x80" instead)
* Character values are indicated by quotation marks. Escapes (such as '\n') are permitted.
* Data sources are given as the first argument (mov %r10,%r11 moves FROM r10 INTO r11).
For the MOV instruction:
* You can append a suffix indicating the amount of data to be moved -- e.g., q for quadword (64 bits), d for doubleword (32 bits), w for word (16 bits), or b for byte (8 bits).
== Resources ==
* CPU Instruction Set and Software Developer Manuals
** AMD: httphttps://developer.amd.com/resources/documentation-articles/developer-guides-manuals/(see the AMD64 Architecture section, particularly the ''AMD64 Architecture Programmer’s Manual Volume 3: General Purpose and System Instructions'')
** Intel: http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html
* Web sites