78 lines
2.9 KiB
Markdown
78 lines
2.9 KiB
Markdown
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# amd64 instructions
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* `;` starts a comment
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## Values
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* __Immediate__, numbers
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* __register__, existing registers
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* __memory__, memory addresses
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## Move
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* `MOV`, from source to destination
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* `LEA`, loads memory address and stores it in the destination. Address can have an offset. Does not dereference `[var]` or `[var+x]`
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* `PUSH` & `POP`, put & delete registers to/from stack.
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## Arithmetic
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* `INC`, increment
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* `DEC`, decrement
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* `ADD`
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* `SUB`, substracts source from dest and stores in dest
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* `MUL` & `IMUL`, result may be stored in upper and lower halfs (rdx:rax)
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* `DIV` & `IDIV`, rax is divided by rbx and may be stored in two halfs as well
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## Conditionals
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* `RET`, return value to the caller
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* `CMP`, compare two values and sets flag. Next instruction is a jump condition to a line number. Works as follows
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* `JE`, `JEZ`, `JLE` ... followed by linenumber
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* `NOP`, `\x90`
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* `CALL` a function
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## Address Handling
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* `[var]`, memory address of var.
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* If var contains an address then after `mov [var], 42` var points to the value 42. `[` dereference.
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## Zero Handling in Registers
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* Move to `eax` will result in zeroing the upper 32 bit of an `rax` register, move to `ax`, `ah`, `al` will not.
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* `MOVZX` zeros anything but the value moved to the register inside of it.
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## Jumps
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* For signed value comparison
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* `JL/JNGE` (SF <> OF) ; Jump if less/not greater or equal
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* `JGE/JNL` (SF = OF) ; Jump if greater or equal/not less
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* `JLE/JNG` (ZF = 1 or SF <> OF); Jump if less or equal/not greater
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* `JG/JNLE` (ZF = 0 and SF = OF); Jump if greater/not less or equal
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* For unsigned value comparison
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* `JB/JNAE` (CF = 1) ; Jump if below/not above or equal
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* `JAE/JNB` (CF = 0) ; Jump if above or equal/not below
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* `JBE/JNA` (CF = 1 or ZF = 1) ; Jump if below or equal/not above
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* `JA/JNBE` (CF = 0 and ZF = 0); Jump if above/not below or equal
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## Flags
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* `eflags` 32bit
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* `rflags` 64bit
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### Status
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* __Zero Flag__ (ZF), 1 if the result of the comparison is equal.
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* __Carry Flag__ (CF), a 1 is stored if a carry is needed after a calculation.
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* __Overflow Flag__ (OF), register overflow is 1
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* __Sign Flag__ (SF), 1 if result is negative.
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* __Adjust/Auxiliary Flag__ (AF), carry flag for BCD.
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* __Parity Flag__ (PF), 1 if the last 8 bits are even.
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* __Trap Flag__ (TF)
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## Calling Conventions
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## cdecl
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## fastcall
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* First four are passed __left to right__
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* int -> RCX, RDX, R8, R9
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* float -> XMM0, XMM1, XMM2, XMM3
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* Rest is __right to left__
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* Basepointer is saved by the caller
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* Return values is passes via `rax` or `xmm0`
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* Caller allocates space for at least four values, so 32 bytes are reserved. `$rsp to $rsp+0x18`
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* Volatile registers are `rax, rcx, r8, r9, r10, r11, xmm0, xmm1, xmm2, xmm3, xmm4, xmm5`. These are destroyed after function call.
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* Nonvolatile registers are `rbx, rbp, rdi, rsi, rsp, r12, r13, r14, r15, xmm6-15` ares saved and restored after function call.
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