[saagarjha]

Here's what works on my Mac, compiled with clang -m32.

  #include <stdio.h>
  
  int main() {
  	int i;                                // Another stack variable
  	printf("%s\n", **(char ***)(&i + 8)); // argv[0]
  	return 0;
  }

Of course, this won't work at all on x86_64 because arguments are passed on registers instead of the stack.

[doomjunky → saagarjha]

On Windows this dependes on the calling convention. The calling convention determines whether function arguments are passed: In order or in reverse order. Who takes care of cleaning the stack: caller or callee? And even if the arguments are passed by stack or CPU registers.

In Visual Studio you can control this behavoir with the __cdecl, __clrcall, __stdcall, __fastcall, __thiscall, __vectorcall [1] calling convention function prefixes, but this also depends on the optimization options [2] of the compiler.

Passing arguments via CPU registers has a huge preformance benefit, but also some drawbacks.

[1]: https://msdn.microsoft.com/en-us/library/984x0h58.aspx

[2]: https://msdn.microsoft.com/en-us/library/46t77ak2.aspx

[saagarjha → doomjunky]

> Passing arguments via CPU registers has a huge preformance benefit, but also some drawbacks.

Like what?

[pjmlp → saagarjha]

On architectures like x86, the set of registers is limited and some are special, so there is some contention going on.

[kbumsik → saagarjha]

I don't know much about AMD64 but if the arguments are passed to registers then how it is possible to retrieve argc/argv later, as other functions likely to touch registers?

[saagarjha → kbumsik]

They're pushed on to the stack if another function will touch them.