Re: [Bug ld/4266] New: hidden alias not found while linking gcj compiled Java class with native C++ lib and CNI binding under Linux x86

[Nick Clifton]

Hi Andreas,

Well I can shed some light on how this problem is happening, although 
not necessarily why:

> de/dbt/simplelibclient/SimpleCPPLib.o:(.data.rel+0x68): undefined reference to
> `hidden alias for de::dbt::simplelibclient::SimpleCPPLib::square(int)'

Looking at libSimpleCPPLib.so, where you would expect to find the 
definition of the alias shows:

  % nm -C SimpleCPPLib/Debug/libSimpleCPPLib.so | grep square
  0000071c t hidden alias for 
de::dbt::simplelibclient::SimpleCPPLib::square(int)
  0000071c T de::dbt::simplelibclient::SimpleCPPLib::square(int)

The "t" is critical.  It indicates that the hidden alias is local to the 
 file and not visible outside the library.  Hence you are getting the 
link-time error.  Looking at the SimpleCPPLib.o file on its own, (ie not 
inside the library) shows:

  % nm -C SimpleCPPLib/Debug/SimpleCPPLib.o | grep square
  00000000 T hidden alias for 
de::dbt::simplelibclient::SimpleCPPLib::square(int)
  00000000 T de::dbt::simplelibclient::SimpleCPPLib::square(int)

ie here the hidden alias is type "T", an exported text symbol.  This 
explains why you can link directly against the SimpleCPPLib.o file and 
obtain a fully resolved executable.


I am not an expert on java, but it seems to me that you should not be 
trying to reference the hidden alias at all, (after all it is hidden). 
Instead SimpleLibClient/de/dbt/simplelibclient/SimpleCPPLib.o ought to 
be referencing the unaliased symbol 
[de::dbt::simplelibclient::SimpleCPPLib::square(int)] which *is* 
exported from libSimpleCPPLib.so.  So to me this implies that this is a 
java compiler (gcj) problem.

If there is a good reason for referencing the hidden alias then the 
problem is either that you should not be linking against the 
libSimpleCPPLib.so library but instead linking against the object file, 
or that the transformation of SimpleCPPLib.o into libSimpleCPPLib.so 
should not be transforming the globally visible hidden alias into a 
local-only hidden alias.

Cheers
  Nick