It seems to be a matter of ABI. For instance, the Itanium C++ ABI reads: If the parameter type is non-trivial for the purposes of calls, the caller must allocate space for a temporary and pass that temporary by reference. And, further: A type is considered non-trivial for the purposes of calls if it has … Read more
If you look at the way the C language stores the parameters on the stack, the way the macros work should become clear:- Higher memory address Last parameter Penultimate parameter …. Second parameter Lower memory address First parameter StackPointer -> Return address (note, depending on the hardware the stack pointer maybe one line down and … Read more
A std::array<int, 3> is 96 bits wide on your implementation. As such the ABI declares that it should be returned in RAX + the low 32 bits of RDX (aka EDX). 4294967296 is 232, in hex it is $1’0000’0000. So the movabs stores 0 in the low order 32 bits of RAX, and 1 in … Read more
Given these two quotes, is the red zone above the stacked return address or below the stacked return address? The red zone is the 128 bytes just below rsp, i.e. rsp – 128 to rsp – 1. Since this red zone is relative to RSP, does it move downward with each push and does it … Read more
From “Intel®64 and IA-32 Architectures Optimization Reference Manual”, section 4.4.2: “For best performance, the Streaming SIMD Extensions and Streaming SIMD Extensions 2 require their memory operands to be aligned to 16-byte boundaries. Unaligned data can cause significant performance penalties compared to aligned data.” From Appendix D: “It is important to ensure that the stack frame … Read more
Simple answer: I use cdecl, stdcall, and fastcall. I seldom use fastcall. stdcall is used to call Windows API functions. Detailed answer (Stolen from Wikipedia): cdecl – In cdecl, subroutine arguments are passed on the stack. Integer values and memory addresses are returned in the EAX register, floating point values in the ST0 x87 register. … Read more
It comes from C function that was declared (in contrast to a C function that was not declared which was common in K&R C). At the time it was coexisting with pascal calling convention (wher the callee cleared the stack), so it kind of made sense to call it after the programming language. Everything you … Read more
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. It is meant to be … Read more
As MSDN says, the correct way to write this is typedef void (__stdcall *MessageHandler)(const Task*);
It depends on the platform. For a Xenon PowerPC, for example, it can be an order of magnitude difference due to a load-hit-store issue with passing data on the stack. I empirically timed the overhead of a cdecl function at about 45 cycles compared to ~4 for a fastcall. For an out-of-order x86 (Intel and … Read more