[PATCH] Use libc_hidden_proto / _def for hidden wchar ifunc symbols.

[Florian Weimer]

On 11/13/2017 02:58 PM, H.J. Lu wrote:

> Now I have question, is there a way to apply attribute_hidden to a function
> depending on architecture? For example, we remove attribute_hidden
> from __wcsnlen, __wcscat, __wcsncpy, __wcpncpy,  __wcschrnul in headers
> under include/.   For x86, we mark them hidden in a header file under
> sysdeps/x86?

We touched this briefly before, when I suggested that we need to 
automate this.  But Joseph thought it wouldn't be possible:

   <https://sourceware.org/ml/libc-alpha/2017-09/msg00113.html>

I don't know if the IFUNC vs hidden symbol issues changes matters 
significantly.  I still don't think it's a good use of our time to 
predict in generic headers what the linker may need in the end, as the 
result of what happens to be emitted by the compiler and assembler.

I'm also not sure if the existing GCC attributes give us sufficient 
control.  I think we need:

   (i)   local call within the current DSO, non-IFUNC implementation
   (ii)  local call within the current DSO, IFUNC implementation
   (iii) non-local call
     (1a) without symbol interposition
     (1b) with symbol interposition (for malloc/free/…)
     and (second choice)
     (2a) through PLT (without --enable-bind-now)
     (2b) without PLT (with --enable-bind-now and recent toolchain)

(ii) looks very similar to (iii)+(1a)+(2b).  But I don't know if that's 
true for all architectures.

Thanks,
Florian