Tutorial by Examples

cdecl is a Windows 32-bit function calling convention which is very similar to the calling convention used on many POSIX operating systems (documented in the i386 System V ABI). One of the differences is in returning small structs. Parameters Parameters are passed on the stack, with the first arg...

This is the default calling convention for 64-bit applications on many POSIX operating systems. Parameters The first eight scalar parameters are passed in (in order) RDI, RSI, RDX, RCX, R8, R9, R10, R11. Parameters past the first eight are placed on the stack, with earlier parameters closer to th...

stdcall is used for 32-bit Windows API calls. Parameters Parameters are passed on the stack, with the first parameter closest to the top of the stack. The callee will pop these values off of the stack before returning. Return Value Scalar return values are placed in EAX. Saved and Clobbered Re...

As parameters (8, 16, 32 bits) 8, 16, 32 bits integers are always passed, on the stack, as full width 32 bits values1. No extension, signed or zeroed, is needed. The callee will just use the lower part of the full width values. //C prototype of the callee void __attribute__((cdecl)) foo(char ...

As parameters (float, double) Floats are 32 bits in size, they are passed naturally on the stack. Doubles are 64 bits in size, they are passed, on the stack, respecting the Little Endian convention1, pushing first the upper 32 bits and than the lower ones. //C prototype of callee double foo(dou...

Parameters The first 4 parameters are passed in (in order) RCX, RDX, R8 and R9. XMM0 to XMM3 are used to pass floating point parameters. Any further parameters are passed on the stack. Parameters larger than 64bit are passed by address. Spill Space Even if the function uses less than 4 paramet...

Padding Remember, members of a struct are usually padded to ensure they are aligned on their natural boundary: struct t { int a, b, c, d; // a is at offset 0, b at 4, c at 8, d at 0ch char e; // e is at 10h short f; // f is at 12h (naturally aligned) lo...