What is the C calling convention?

In the C calling convention subprogram parameters are pushed on the stack by the caller from right to left. The caller itself is in charge of cleaning up the stack after the call. In addition, the name of a routine with C calling convention is mangled by adding a leading underscore.

How do you specify a calling convention?

Calling conventions specify how arguments are passed to a function, how return values are passed back out of a function, how the function is called, and how the function manages the stack and its stack frame. In short, the calling convention specifies how a function call in C or C++ is converted into assembly language.

What calling convention does GCC use?

The cdecl (pronounced see-dec-el, short for “C declaration”) calling convention is extremely common as it’s the default x86 (32-bit) calling convention on today’s most popular compilers including GCC, MSVC, and LLVM. It has the following properties: The caller places all arguments to the callee on the stack.

What is the difference between Stdcall and cdecl?

__cdecl is the default calling convention for C and C++ programs. Because the stack is cleaned up by the caller, it can do vararg functions. The __cdecl calling convention creates larger executables than __stdcall, because it requires each function call to include stack cleanup code.

What is a saved register?

Callee-saved registers (AKA non-volatile registers, or call-preserved) are used to hold long-lived values that should be preserved across calls.

What is x64 shadow space?

2 Answers. 2. 40. The Shadow space (also sometimes called Spill space or Home space) is 32 bytes above the return address which the called function owns (and can use as scratch space), below stack args if any. The caller has to reserve space for their callee’s shadow space before running a call instruction.

Is Fastcall faster?

Since it typically saves at least four memory accesses, yes it is generally faster.

What is __ Stdcall in C++?

__stdcall is the calling convention used for the function. This tells the compiler the rules that apply for setting up the stack, pushing arguments and getting a return value.

Is RAX a caller saved register?

The registers RAX, RCX, RDX, R8, R9, R10, R11 are considered volatile (caller-saved). The registers RBX, RBP, RDI, RSI, RSP, R12, R13, R14, and R15 are considered nonvolatile (callee-saved).

What is the __fastcall calling convention in x64?

Given the expanded register set, x64 uses the __fastcall calling convention and a RISC-based exception-handling model. The __fastcall convention uses registers for the first four arguments and the stack frame to pass additional arguments.

What is the difference between x86 and x64 calling conventions?

Overview of x64 calling conventions Two important differences between x86 and x64 are the 64-bit addressing capability and a flat set of 16 64-bit registers for general use. Given the expanded register set, x64 uses the __fastcall calling convention and a RISC-based exception-handling model.

What is the x64 calling convention in UEFI?

Microsoft X64 Calling Convention – The Microsoft x64 calling convention is followed on Windows and pre-boot UEFI (for long mode on x86-64). It uses registers RCX, RDX, R8, R9 for the first four integer or pointer arguments (in that order), and XMM0, XMM1, XMM2, XMM3 are used for floating point arguments.

What is the calling convention of AMD64 ABI in Linux?

The calling convention of the System V AMD64 ABI is followed on GNU/ Linux. The registers RDI, RSI, RDX, RCX, R8, and R9 are used for integer and memory address arguments and XMM0, XMM1, XMM2, XMM3, XMM4, XMM5, XMM6 and XMM7 are used for floating point arguments. For system calls, R10 is used instead of RCX.