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Re: [PATCH] Avoid invoking ranlib on libbackend.a
On Mon, Jul 18, 2016 at 1:35 PM, Segher Boessenkool
<segher@kernel.crashing.org> wrote:
> On Sun, Jul 17, 2016 at 10:04:13PM -0400, Patrick Palka wrote:
>> I did some digging to figure out the origin of libbackend.a. It was was
>> created to work around a command line length limit on a VAX system
>> (https://gcc.gnu.org/ml/gcc-bugs/2000-06/msg00438.html). The 1600 byte
>> command line that links cc1plus was too large for this system, so
>> libbackend.a was introduced and used in place of $(OBJS) to reduce the
>> size of this command line.
>
> As Zack said in that thread, at the top of the mail you refer to here:
> "Putting the back end in a library seems like a good idea to me, never
> mind whether or not we're really hitting command line length limits."
>
> Many people agree with that. Some, anyway.
>
>> I suppose rebuild times could instead be further reduced by splitting
>> libbackend.a into multiple logical archives. It would also be a small
>> step towards making GCC more modular.
>
> Is it faster to not have one big archive? There are nine compilers.
>
> If you want to add -s to the ar flags (it is POSIX, most systems should
> have it by now), you should add a configure check (or find one, there is
> bound to be one somewhere already) to test for it, and then add it to
> AR_FLAGS (and there is also AR_CREATE_FOR_TARGET, it may be useful to
> add it there as well -- needs a separate test of course).
>
> Or, if using GNU ar, you can even use -S, if that helps (after testing
> for it in configure, of course).
While eliding ranlib sounds like a no-brainer the real benefit (I/O wise) is
when you get rid of the archive or save link time by creating a (partially)
linked DSO. ISTR Michael Matz has patches to do that. Whether it's
portable enough is another question (I suppose it simply uses libtool).
Richard.
>
> Segher