[Mesa-dev] Can --enable-shared-glapi die?

[Adam Jackson]

On 7/24/12 1:45 PM, Ian Romanick wrote:
> On 07/23/2012 12:59 PM, Ian Romanick wrote:
>> Perhaps someone can refresh my memory as to what exactly this option
>> does?  Can we make this the default and remove the option from configure?
>
> Thanks to all for the refresher.  Off-list someone raised another issue
> to me that seems like a deal breaker.  If an application links with a
> libGL that uses libglapi it appears that the application gets implicitly
> linked with libglapi (as shown by objdump -x | grep -i need).

This part is actually dependent on whether the app is built with 
--copy-dt-needed-entries.  Historically that's been the default, but 
most modern distros have switched to --no-copy-etc, in which case the 
app will _not_ get a DT_NEEDED on libglapi just for linking against 
libGL.  This is good; apps shouldn't be made accidentally fragile based 
on implementation details of the libraries they link against.  But it 
does require a modestly recent linker with that option, or with it under 
the old spelling of --no-add-needed.

> This will
> cause the application to fail if a non-glapi libGL (i.e., any of the
> closed-source drivers) is later installed.  The problem seems to be that
> symbols like glBegin are in libglapi.

That doesn't jive with what my linker says, at least looking at an F16 
machine:

atropine:~% nm -aD --defined /usr/lib/libglapi.so
0002f060 A __bss_start
0002f060 A _edata
0002fcf4 A _end
000178a8 T _fini
0002fcf0 B _glapi_Context
0002f05c D _glapi_Dispatch
00016d60 T _glapi_add_dispatch
00016cd0 T _glapi_check_multithread
00017420 T _glapi_get_context
00017600 T _glapi_get_dispatch
00016d50 T _glapi_get_dispatch_table_size
00016f80 T _glapi_get_proc_address
00017000 T _glapi_get_proc_name
00016f00 T _glapi_get_proc_offset
00017030 T _glapi_noop_enable_warnings
00016cf0 T _glapi_set_context
00016d20 T _glapi_set_dispatch
00017040 T _glapi_set_warning_func
00017010 T _glthread_GetID
00004ef8 T _init

That's all libGL-to-dispatch bridging, it's not app API.  There's no 
reason the app would need a DT_NEEDED against libglapi.

- ajax