[Ffmpeg-devel] Re: ffmpeg on OS X

[Lina Pezzella]

On Oct 18, 2005, at 7:31 PM, ffmpeg-devel-request at mplayerhq.hu wrote:

> Also, I had to use -undefined suppress for vhook libs... not sure how
> it's meant to be used, but I guess binaries
> using this libs should actually link with all the required libs).

The use of -undefined suppress means that ld won't check for  
undefined symbols when linking.

>
> -SHFLAGS="-dynamiclib -Wl,-single_module,-undefined,dynamic_lookup"
> +SHFLAGS="-dynamiclib -Wl"

Leaving out the -single_module will break 64-bit systems, as the  
default (multi_module) is 32-bit only. Not that I have a 64-bit  
system to test this on...but things seem to be moving that way, so  
this may not be a smart change.

> -       SHFLAGS += -flat_namespace
> +       SHFLAGS += -flat_namespace -undefined suppress

Forcing -flat_namespace is not exactly a good thing -- this should  
probably be changed at some point. The Mac OS X static linker under  
flat_namespace records only the names of libraries, not which  
functions are to be found in which library. Thus if you happen to  
link to two libraries which define the same symbol, you will get an  
error. This is probably not desirable behavior. The default is now a  
two level namespace, which fixes this problem. The issue with the two  
level namespace is that all undefined references must be satisfied at  
static link time, thus -undefined suppress is not an option with two  
level namespace. Short of fixing the unresolved symbols in the code  
(which is really what should happen), the only option I know of is to  
do -undefined dynamic_lookup (which is a 10.3 and greater-only feature).

Hopefully this helps more than it confuses.

--Lina Pezzella
Gentoo Developer