Wiki/assembly.md

Assembly

Labels

• .cfi_startproc: marks the beginning of a function
• .cfi_endproc: marks the end of a function
• .L{A-Z}*{0-9}+: local label
  • .L{0-9]+: jump target
  • .L{A-Z}+{0-9}+: other purpose
    • FB: function begin
    • FE: function end

AT&T

• source comes before destination
• mnemonic suffixes indicate the size of the operands (q for quad, etc.)
• registers are prefixed with % and immediate values with $
• effective addresses are in the form DISP(BASE, INDEX, SCALE) (DISP + BASE + INDEX * SCALE)
• Indirect jump/call operands indicated with * (as opposed to direct).

Resources

• Opcodes: https://www.felixcloutier.com/x86/index.html
• General Intel instructions: https://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.html
• More performance oriented: https://www.agner.org/optimize/

Registers

Overview

| --- | --- | --- | --- |

64-bit register	Lower 32 bits	Lower 16 bits	Lower 8 bits
rax	eax	ax	al
rbx	ebx	bx	bl
rcx	ecx	cx	cl
rdx	edx	dx	dl
rsi	esi	si	sil
rdi	edi	di	dil
rbp	ebp	bp	bpl
rsp	esp	sp	spl
r8	r8d	r8w	r8b
r9	r9d	r9w	r9b
r10	r10d	r10w	r10b
r11	r11d	r11w	r11b
r12	r12d	r12w	r12b
r13	r13d	r13w	r13b
r14	r14d	r14w	r14b
r15	r15d	r15w	r15b

Calling Conversions

• Args: RDI, RSI, RDX, RCX, R8, R9
  • System Calls: R10 (instead of RCX)
• Return: RAX
• Callee-Saved: RBX, RBP, R12, R13, R14, R15
• Caller-Saved: RAX, RCX, RDX, RDI, RSI, R8, R9