What is x64 assembly?

For years, PC programmers used x86 assembly to write performance-critical code. x64 is a generic name for the 64-bit extensions to Intel‟s and AMD‟s 32-bit x86 instruction set architecture (ISA). AMD introduced the first version of x64, initially called x86-64 and later renamed AMD64.

Which registers is the callee responsible for preserving?

Call-preserved, aka callee-saved or non-volatile registers keep their values across function calls. This is useful for loop variables in a loop that makes function calls, or basically anything in a non-leaf function in general.

What 64-bit register will hold the return value of a function?

Integer return values up to 64 bits in size are stored in RAX while values up to 128 bit are stored in RAX and RDX. Floating-point return values are similarly stored in XMM0 and XMM1.

Which registers must the calling code preserve?

3 Answers. r12 , r13 , r14 , r15 , rbx , rsp , rbp are the callee-saved registers – they have a “Yes” in the “Preserved across function calls” column.

What does Callq mean in assembly?

The callq instruction takes one operand, the address of the function being called. It pushes the return address (current value of \%rip , which is the next instruction after the call) onto the stack and then jumps to the address of the function being called.

What is a callee in C?

Calling conventions constrain both callers and callees. A caller is a function that calls another function; a callee is a function that was called. The currently-executing function is a callee, but not a caller.

Which are function calling conventions in C?

There are three major calling conventions that are used with the C language on 32-bit x86 processors: STDCALL, CDECL, and FASTCALL. In addition, there is another calling convention typically used with C++: THISCALL.

What is calling convention in C?

Calling conventions are a standardized method for functions to be implemented and called by the machine. A calling convention specifies the method that a compiler sets up to access a subroutine. In short, the calling convention specifies how a function call in C or C++ is converted into assembly language.

What is a caller in C?

A caller is a function that calls another function; a callee is a function that was called.