Linking cgit with Lua using -Wl,-E

Linking cgit with Lua using -Wl,-E

[@ 2016-10-16 5:30 UTC (permalink / raw)]

Hello,

on my system I wanted to link cgit with lua, so that lua can load the (lua)crypto.so module.  For this to work the symbol lua_gettop has to be exported by cgit.  I managed this by passing "-Wl,-E" to the linker, when compiling cgit.

I use ld 2.27.51.20161011, gcc 6.2.1 20161011 and the newest ever git.

Greetings
   ?????

Linking cgit with Lua using -Wl,-E

[john]

On Sun, Oct 16, 2016 at 07:30:08AM +0200, ????? ???????? wrote:
> on my system I wanted to link cgit with lua, so that lua can load the
> (lua)crypto.so module.  For this to work the symbol lua_gettop has to
> be exported by cgit.  I managed this by passing "-Wl,-E" to the
> linker, when compiling cgit.

How are you linking to liblua?  I thought we normally linked that
dynamically so the symbol should be exported from the shared library
even if the cgit binary does not export symbols.

Linking cgit with Lua using -Wl,-E

[@ 2016-10-21 7:54 UTC (permalink / raw)]

Hello John,

liblua is linked statically. This is what you get, when you compile Lua from source (no liblua.so).

Greetings
?????

On 10/16/2016 01:55 PM, John Keeping wrote:
> On Sun, Oct 16, 2016 at 07:30:08AM +0200, ????? ???????? wrote:
>> on my system I wanted to link cgit with lua, so that lua can load the
>> (lua)crypto.so module.  For this to work the symbol lua_gettop has to
>> be exported by cgit.  I managed this by passing "-Wl,-E" to the
>> linker, when compiling cgit.
>
> How are you linking to liblua?  I thought we normally linked that
> dynamically so the symbol should be exported from the shared library
> even if the cgit binary does not export symbols.
>

Linking cgit with Lua using -Wl,-E

[john]

I assume it's possible to build a shared library; I get both shared and
static installed by my package manager.

It looks like there is some performance concern about using a shared
libary for Lua[1], but I doubt performance is critical for most uses
with CGit so I would recommend building and linking to the Lua shared
library if possible.

If you need to link to the static library, I think it will be safer to
use:

	-rdynamic -fvisibility=hidden

but that will still expose all of the symbols from libgit.a, which was
not designed to be used as a library by third-party code and thus does
not prefix its symbols, so you still have to be wary of symbol
collisions with other libraries.

[1] http://article.gmane.org/gmane.comp.lang.lua.general/18519

On Fri, Oct 21, 2016 at 09:54:23AM +0200, ????? ???????? wrote:
> liblua is linked statically. This is what you get, when you compile
> Lua from source (no liblua.so).
> 
> On 10/16/2016 01:55 PM, John Keeping wrote:
> > On Sun, Oct 16, 2016 at 07:30:08AM +0200, ????? ???????? wrote:
> >> on my system I wanted to link cgit with lua, so that lua can load the
> >> (lua)crypto.so module.  For this to work the symbol lua_gettop has to
> >> be exported by cgit.  I managed this by passing "-Wl,-E" to the
> >> linker, when compiling cgit.
> >
> > How are you linking to liblua?  I thought we normally linked that
> > dynamically so the symbol should be exported from the shared library
> > even if the cgit binary does not export symbols.
> >

Linking cgit with Lua using -Wl,-E

[@ 2016-11-06 10:13 UTC (permalink / raw)]

Hello,

it is possible to build a shared library, but you shall assume, that the ones who build cgit from source code, build also liblua from source code.  And the result is static liblua.a .



On 10/23/2016 05:55 PM, John Keeping wrote:
> I assume it's possible to build a shared library; I get both shared and
> static installed by my package manager.
>
> It looks like there is some performance concern about using a shared
> libary for Lua[1], but I doubt performance is critical for most uses
> with CGit so I would recommend building and linking to the Lua shared
> library if possible.
>
> If you need to link to the static library, I think it will be safer to
> use:
>
> 	-rdynamic -fvisibility=hidden
>
> but that will still expose all of the symbols from libgit.a, which was
> not designed to be used as a library by third-party code and thus does
> not prefix its symbols, so you still have to be wary of symbol
> collisions with other libraries.
>
> [1] http://article.gmane.org/gmane.comp.lang.lua.general/18519
>
> On Fri, Oct 21, 2016 at 09:54:23AM +0200, ????? ???????? wrote:
>> liblua is linked statically. This is what you get, when you compile
>> Lua from source (no liblua.so).
>>
>> On 10/16/2016 01:55 PM, John Keeping wrote:
>>> On Sun, Oct 16, 2016 at 07:30:08AM +0200, ????? ???????? wrote:
>>>> on my system I wanted to link cgit with lua, so that lua can load the
>>>> (lua)crypto.so module.  For this to work the symbol lua_gettop has to
>>>> be exported by cgit.  I managed this by passing "-Wl,-E" to the
>>>> linker, when compiling cgit.
>>>
>>> How are you linking to liblua?  I thought we normally linked that
>>> dynamically so the symbol should be exported from the shared library
>>> even if the cgit binary does not export symbols.
>>>