On Wed, Oct 28, 2020 at 11:40 AM Nick Bowler <nbow...@draconx.ca> wrote: > > On 2020-10-28, Zack Weinberg <za...@panix.com> wrote: > > On Wed, Oct 28, 2020 at 2:16 PM Nick Bowler <nbow...@draconx.ca> wrote: > >> On 2020-10-28, H.J. Lu <hjl.to...@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. > > Since this check cannot be done inside a rule, testing LDFLAGS at make > time is probably impractical to do portably. > > However I think I misunderstood the impact of this option on first > reading. > > I am not aware of any portability concerns with including "+" in > commands, if this is literally the only difference it should be OK > to just always include it (after ensuring that "make -n" is respected > portably in the command). >
"make -n" will execute the recipe with the "+" prefix. But --jobserver is off by default. People who use --jobserver prefer a working GCC -flto=jobserver over a broken "make -n". -- H.J.
