Re: duplicate -lgcc --as-needed -lgcc_s --no-as-needed

[Nix <nix at esperi dot org dot uk>]

On 2 Jun 2005, Peter S. Mazinger murmured:
> On Thu, 2 Jun 2005, Jakub Jelinek wrote:
> 
>> On Thu, Jun 02, 2005 at 01:59:46PM +0200, Peter S. Mazinger wrote:
>> > Hello!
>> > 
>> > the sequence used for linking on x86 (but most archs will have it too)
>> > -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s 
>> > --no-as-needed
>> > contains duplicate. Is this really necessary?
> 
> Is it necessary to have it before -lc and after?

Probably not.  I think the first --as-needed -lgcc_s --no-as-needed
could probably be removed, but this would actually introduce complexity:
both of the `-lgcc --as-needed -lgcc_s- --no-as-needed' sequences come
from expansion of the same %G spec, so we'd have to introduce a new spec
letter just to deal with this, for, effectively, no benefit.  (Maybe
we'd save an unmeasurably small of time in the link phase.)

>> > Will the '--as-needed -lgcc_s --no-as-needed' ever apply?
>> 
>> > The missing symbols will be found in -lgcc.
>> 
>> That's not true.  The EH stuff is not in -lgcc, so if -lc needs it,
>> it wouldn't be found.
> 
> so this construct is used only to get EH stuff from libgcc_s.so? Is there 
> stuff in libgcc.a that is not present in libgcc_s.so too? If not, what 
> about moving this around (or remove -lgcc) and get everything from 
> libgcc_s, if we already depend on it?

The point of that trickery is to avoid introducing a dependency on the
shared libgcc for programs that don't use exception handling. If they
do, it'll come from the shared libgcc: otherwise, the shared libgcc gets
entirely dropped thanks to --as-needed. (This is *not* quite the same as
dropping it for C programs and keeping it for C++ programs: C programs
can be linked with -fexceptions for the same of exception propagation
from C++, and then they'd pull in symbols from libgcc_s, even if they
are themselves not using the symbol anywhere else: perhaps they're a
shared library, or will dlopen() something written in C++ which may
throw.)

-- 
`Once again, I must remark on the far-reaching extent of my
 ladylike nature.' --- Rosie Taylor