Re: Some form of __thiscall support
- From: Mike Pall <mike-1206@xxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Fri, 29 Jun 2012 10:57:06 +0200
I wrote:
> Claire Lewis wrote:
> > It would be pretty handy to have some sort of support for
> > marking functions as “__thiscall” calling convention (or
> > equivalent), such that one could directly use the decorated C++
> > names, passing ‘this’ as the first argument.
>
> Actually, the __thiscall declaration already works. But the call
> setup is still wrong.
Umm, I was wrong. It's already implemented correctly. I just never
bothered to actually try it ... :-)
Here's some sample C++ code:
class __declspec(dllexport) Foo {
public:
Foo(int a);
int get();
int x;
};
Foo::Foo(int a) { x = a; }
int Foo::get() { return x; }
Compile that into test.dll with MSVC on Windows/x86.
Then run the C++ code with this Lua program:
local ffi = require("ffi")
ffi.cdef[[
typedef struct { int x; } Foo;
Foo * __thiscall Foo_new(Foo *, int) asm("??0Foo@@QAE@H@Z");
int __thiscall Foo_get(Foo *) asm("?get@Foo@@QAEHXZ");
]]
local lib = ffi.load("a.dll")
local foo = ffi.new("Foo")
lib.Foo_new(foo, 42)
print(foo.x)
print(lib.Foo_get(foo))
The name mangling is specific to MSVC and x86. The mangled names
for x64 are "??0Foo@@QEAA@H@Z" and "?get@Foo@@QEAAHXZ". GCC has
its own C++ name mangling scheme.
Note: __thiscall is only needed for C++ methods compiled with MSVC
on Windows/x86. Windows/x64 has a unified calling convention. GCC
doesn't use __thiscall, even on Windows/x86.
--Mike
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