Re: PATCH: Build shared libraries with -Bsymbolic-functions

["H. J. Lu" <hjl at lucon dot org>]

On Wed, Jan 31, 2007 at 05:21:11PM -0500, Andrew Pinski wrote:
> > 
> > On Sun, Jan 14, 2007 at 10:47:41AM -0800, H. J. Lu wrote:
> > > On Sun, Jan 14, 2007 at 01:30:07PM -0500, Andrew Pinski wrote:
> > > > > I checked in the libjava part. Here is the updated patch for other
> > > > > libraries. If someone can give me a list of functions in libobjc
> > > > > which should be overridable, I will add them to the dynamic list
> > > > > for libobjc.
> > > > 
> > > > All except for the class functions themselves.  For libobjc, a better
> > > > way of doing this is actually marking the class methods as hidden as they
> > > > are never called directly.
> > > 
> > > I assume *.m files have class functions and other files have non-class
> > > functions which may be overrable by programmers. Is that correct?
> > > 
> > > What about functuons with the prefixes of __?
> > 
> > I took a look at
> > 
> > http://www.dribin.org/dave/blog/archives/2006/04/22/tracing_objc/
> > http://developer.apple.com/documentation/DeveloperTools/Conceptual/DynamicLibraries/Articles/UsingDynamicLibraries.html#//apple_ref/doc/uid/TP40002182-DontLinkElementID_32
> 
> 
> Apple's documention is about the NeXT runtime and not the GNU runtime so those don't
> apply really. The first link also only applies to the NeXT runtime.  

My point is a user shouldn't assume that he/she can override
global function call references within libobjc, which is the only
visible impact my patch has.

> 
> I have a patch for libobjc to use -fvisibility=hidden.  The number of functions inside
> the Objective-C runtime is little so the issue of getting binding faster will not help
> it that much.  Also I am working on just getting the class's methods marked hidden.
> 
> Really your patch only helps targets where GNU binutils works and only where
> that specific option has been added (which is not going to be released until later
> this year).  And my patches will help all targets even with older binutils.
> 
> I would rather libobjc be done differently than the other target libraries because
> there is no reason to include this option when there are better ways of getting this
> working correctly.

-fvisibility=hidden only works on global functions which aren't
the part of libobjc ABI. For example,

BOOL objc_hash_is_key_in_hash (cache_ptr cache, const void *key);

is in hash.h and user can call it. It can't be hidden. But there
is

[hjl@gnu-26 .libs]$ readelf  --wide -r libobjc.so.2  | grep objc_hash_is_key_in_hash
0000000000217910  0000010700000007 R_X86_64_JUMP_SLOT 000000000000cde0 objc_hash_is_key_in_hash + 0

My approach will remove this relocation.


H.J.