visibility and -Wl,--version-script

[Mathieu Lacage]

On Fri, Jul 18, 2008 at 8:43 PM, Brian Dessent <brian@dessent.net> wrote:
> Mathieu Lacage wrote:
>
>> Right, but if I do that, gcc will use GOT/PLT lookups to access these
>> symbols even when doing accesses from within the library and that is
>> precisely what I would like to avoid.
>
> In that case you need to create a second alias of the symbol with hidden
> visibility for internal use within the library.  The Drepper paper
> explains how to do this in section 2.2.7.
>
> The problem with doing this in C++ code is that the alias declaration
> needs the assembler name of the function which includes the mangling,
> and there's no way to automatically generate that short of compiling a
> testcase and looking at the assembly output.  You could arrange for this
> to be done automatically with some kind of multi-pass compilation scheme
> with tons of macro magic: first run g++ -S over the source, then use a
> perl/awk/whatever script to extract the mangled names of exported
> functions and substitute them back into a second compilation of the same
> file with the alias declarations added.  To me that sounds like a
> fragile and complicated way of achieving a modest optimization.  The
> wrapper function approach mentioned in that same section is probably the
> best way to go in the face of C++.

Both options require different names to be used when calling a
function internally and when calling a function through the GOT/PLT.
That is clearly not something I will be able to retrofit in our
codebase. So, it looks like all bets are off and that I should just
build everything statically without -fpic if  I want to avoid the
GOT/PLT lookups.

Mathieu
-- 
Mathieu Lacage <mathieu.lacage@gmail.com>