Re: [Mingw-users] Definition is marked dllimport

[Aaron W. L. <aar...@aa...>]

It might be helpful to look up the exact documented semantics of 
dllimport on GCC here:
http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function%20Attributes

Quoting:
dllimport
On Microsoft Windows targets, the dllimport attribute causes the 
compiler to reference a function or variable via a global pointer to a 
pointer that is set up by the Microsoft Windows dll library. The pointer 
name is formed by combining _imp__ and the function or variable name. 
The attribute implies extern storage.
Currently, the attribute is ignored for inlined functions. If the 
attribute is applied to a symbol definition, an error is reported. If a 
symbol previously declared dllimport is later defined, the attribute is 
ignored in subsequent references, and a warning is emitted. The 
attribute is also overridden by a subsequent declaration as dllexport.

When applied to C++ classes, the attribute marks non-inlined member 
functions and static data members as imports. However, the attribute is 
ignored for virtual methods to allow creation of vtables using thunks.

On cygwin, mingw and arm-pe targets, __declspec(dllimport) is recognized 
as a synonym for __attribute__ ((dllimport)) for compatibility with 
other Microsoft Windows compilers.

The use of the dllimport attribute on functions is not necessary, but 
provides a small performance benefit by eliminating a thunk in the dll. 
The use of the dllimport attribute on imported variables was required on 
older versions of GNU ld, but can now be avoided by passing the 
--enable-auto-import switch to ld. As with functions, using the 
attribute for a variable eliminates a thunk in the dll.

One drawback to using this attribute is that a pointer to a function or 
variable marked as dllimport cannot be used as a constant address. The 
attribute can be disabled for functions by setting the 
-mnop-fun-dllimport flag.


Aaron