Re: luajit-FFI suggestions

[Scott Shumaker <sshumaker@...>]

> If you export them, then they don't get stripped.

I've tried both: __attribute__((__visibility__("default"))), #pragma
GCC visibility push(default) - and neither one seems to do the trick.
Is there some other trick I need to get this to work (gcc version
4.4.3 (GCC), cross-compiling for android).

Scott



On Thu, Jun 9, 2011 at 12:31 PM, Mike Pall <mikelu-1106@mike.de> wrote:
> Scott Shumaker wrote:
>> - Many of these functions are only designed to be called by LUA.
>> Since they aren't referenced anywhere else in my code, they tend to
>> get stripped out at link-time.  My current workaround is to reference
>> them in another translation unit, which is annoying.
>
> If you export them, then they don't get stripped.
>
>> - The functions are only addressable with the exact same name in the
>> ffi.C namespace.  This isn't always desirable.  For example, I wanted
>> to use the built-in htonl, htons and friends.  However, they are
>> actually defined as macros on my system.  This can be trivially fixed
>> by writing a wrapper function.  However, I can't name the wrapped
>> function 'htonl', or else I'll have conflicts with the macro.  So I
>> named my functions htonl2, etc - which means I have to address them
>> through FFI as 'htonl2'.  Often, I'd like to be able to tell FFI what
>> name to refer to them, and which namespace to stick them in.
>
> The FFI supports GCC's symbol renaming facility:
>
>  uint32_t htonl(uint32_t) asm("htonl2");
>
> Also, calling a C function for htonl seems excessive. Use this
> instead:
>
>  local bit = require("bit")
>  local htonl = ffi.abi("le") and bit.bswap or bit.tobit
>
>> - My functions don't work at all unless I set -Wl,--export-dynamic in
>> my makefile - which isn't something I really want to do.
>
> Umm, why? Shared libraries also export all of their visible
> functions ...
>
>> I have a suggestion that would solve all 3 of these problems.
>>
>> What about adding a function to ffi that is something along the lines
>> of luaL_register / lua_openlib?
>>
>> static const struct ffi_reg netFuncs [] = {
>>     {"htonl",htonl2},
>>     {"ntohl",ntohl2},
>>     {NULL, NULL}  /* sentinel */
>>   };
>>
>> ffi_register(L, "net", netFuncs);
>
> You can already do that. Return a pointer to a struct of function
> pointers from C to Lua and use the struct like a namespace:
>
> ffi.cdef[[
> struct mylib {
>  int (*foo)(int);
>  int (*bar)(int);
>  // ...
> };
> struct mylib *getmylib(void);
> ]]
>
> local mylib = ffi.C.getmylib()
> print(mylib.foo(1))
> print(mylib.bar(2))
>
> --Mike
>
>