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A very useful tool to debug such DLL problems is Dependency Walker
[1]. It can tell you what dependencies a DLL has (and it displays
warning if it's unable to find them). It is also useful to examine
exported symbols, and check that your luaopen_foo is properly named
and not mangled.

And to find out why -static-libgcc solves the problem, and how to
solve it with MSVC, you will have to provide more details, such as
what DLL exactly is reported missing, what unusual things you might
have in your PATH, or whether you may have several foo.dll files in
the PATH (for example one for the C/C++ library, and one for the Lua/C
binding module).


my %PATH% was "classic", nothing strange in it (i checked it with

echo $PATH | awk 'BEGIN { FS=":"} {for (i=1; i<NF; i++) print $i}'

(sorry i don't know how to do it fast with Lua) )

I've got only one "foo.dll". I didn't verify if windows installed one in its system-path, but i don't think so.

I checked name mangle, which was ok with "objdump" (or "nm", don't remember). Anyway, compiling with static version of gcc standard lib solves the issue, so no name mangling here.

And well i do know why i had to add "-static-libgcc".
I wrote the short version, as the story seems to raise few interest. For those who are more interested, here's the full story

<found on a forum>
All MinGW executables that uses C/C++ routines, classes and libs are necessary linked against libgcc_s_dwxx-x.dll (GNU C lib) and libstdc++-xx.dll (GNU C++ STD lib) All these .dll can be found at the compiler's /bin directory.
All you have to do is to copy&paste those into your main executable's path.
For a static link version of this libs, you can add "-static-libgcc -static-libstdc++" to your compiler flags and you won't need this .dll anymore. Your executable will be dramatically heavier, due to the internal addition of their contents, but it should be OK.
</found on a forum>

Now, the mystery is:
Why in shell (CMD or MSYS), during the lua's require, i got this error:

> require "libfoo"
error loading module 'libfoo' from file '.\libfoo.dll':
       Le module spécifié est introuvable.
       (above mean that "specified module could'nt be found)

But why when i launch the lua script from explorer (in my case "total commander", but that's the same from explorer) i got another error ?
This time, the error was about the missing libgcc_s...dll

I can understand that i don't have problems with MSYS, but the same error (that is, missing GNU libc++) should raise with CMD, as it has nothing to do with GNU C++ standard lib.

What is missing is something like "strace" under windows, which could help to solve this sort of issues (Lua probably hang on this, and report a very generic error message). So i will give a try for dependency-walker, next time i have a MS-windows in the neighborhood (no windows here for trying, sorry).

I gave a try with MSVC for trying to figure it out, but i'd rather like using GNU's. That's odd that MSVC couldn't compile properly my lib, and perhaps it's another problem (i can't believe that Microsoft C++ standard library is missing in system32 :p ).

Thanks for the link, i guess it will be useful next time !