Re: [PATCH] Add --jobserver/jobserver option for GCC -flto=jobserver

[Zack Weinberg]

On Wed, Oct 28, 2020 at 2:16 PM Nick Bowler <nbowler@draconx.ca> wrote:
> On 2020-10-28, H.J. Lu <hjl.tools@gmail.com> wrote:
> > GCC introduced some time ago option -flto=jobserver in order to use the
> > GNU Make jobserver when parallelising LTO builds.  It is actually a
> > similar "recursive make".  When doing a recursive make, you need to
> > place a '+' character at the beginning of the recipe line in order to
> > let GNU Make pass the jobserver file descriptors to the child processes.
> >
> > Add the --jobserver option to add a '+' character to the recipe line in
> > program.am and ltlibrary.am.
...
> Surely this needs to be a configure-time option, perhaps combined
> with some sort of configure test, since otherwise users won't get
> this choice, right?  As an automake option the choice made by whomever
> prepares the distribution will get baked into distributed Makefile.in
> files...

I was going to say something very similar: there shouldn't be an
option at all.  The decision of whether or not to put + at the
beginning of the recipe line should be made _when make is run_, based
on whether -flto=jobserver actually appears in $(LDFLAGS) or wherever.

> This will break "make -n", won't it?  Some sort of test of $(MAKEFLAGS)
> is probably required in this command.

I concur with this as well.

zw