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). Cheers, Nick
