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Re: [PATCH] Deduce automatically number of cores for -flto option.


> and see that in some cases jobserver is 0 and in other cases jobserver is 1.
> Examples of both:
> 0 kw -j2 --jobserver-auth=3,6 -- 
> total 0
> lrwx------. 1 jakub jakub 64 Jul 31 10:41 0 -> /dev/pts/4
> l-wx------. 1 jakub jakub 64 Jul 31 10:41 1 -> pipe:[75026106]
> lr-x------. 1 jakub jakub 64 Jul 31 10:41 10 -> /usr/src/gcc/obj/gcc/libgcc_s.so
> lr-x------. 1 jakub jakub 64 Jul 31 10:41 13 -> /usr/lib64/libc.so
> lr-x------. 1 jakub jakub 64 Jul 31 10:41 18 -> /usr/src/gcc/obj/gcc/libgcc_s.so
> l-wx------. 1 jakub jakub 64 Jul 31 10:41 2 -> /tmp/ccX4y4r3.le
> l-wx------. 1 jakub jakub 64 Jul 31 10:41 9 -> pipe:[46167136]
> 1 kw -j2 --jobserver-auth=3,6 -- 
> total 0
> lrwx------. 1 jakub jakub 64 Jul 31 10:41 0 -> /dev/pts/4
> l-wx------. 1 jakub jakub 64 Jul 31 10:41 1 -> /tmp/cchSvmBt
> lr-x------. 1 jakub jakub 64 Jul 31 10:41 10 -> /usr/lib64/crtn.o
> lrwx------. 1 jakub jakub 64 Jul 31 10:41 2 -> /dev/pts/4
> lr-x------. 1 jakub jakub 64 Jul 31 10:41 3 -> /usr/lib64/crt1.o
> lr-x------. 1 jakub jakub 64 Jul 31 10:41 4 -> /usr/lib64/crti.o
> lr-x------. 1 jakub jakub 64 Jul 31 10:41 5 -> /usr/src/gcc/obj/gcc/crtbegin.o
> lr-x------. 1 jakub jakub 64 Jul 31 10:41 6 -> /usr/src/gcc/obj/gcc/testsuite/gcc/c_lto_20081125_0.o
> lr-x------. 1 jakub jakub 64 Jul 31 10:41 7 -> /usr/src/gcc/obj/gcc/testsuite/gcc/c_lto_20081125_1.o
> lr-x------. 1 jakub jakub 64 Jul 31 10:41 8 -> /usr/src/gcc/obj/gcc/crtend.o
> l-wx------. 1 jakub jakub 64 Jul 31 10:41 9 -> pipe:[46167136]
> 
> so, if one is lucky enough and at least one of the two file descriptors in
> MAKEFLAGS --jobserver-auth= is closed, it will work fine, but if they are
> open, even when they have nothing to do with make, it will fail miserably.

I see, so the problem is that lto-wrapper is executed via plugin from
gold which already used the file descriptors for something else?

This seems a bit of problem since gold opens it before we get to
lto-plugin (most probably) so i do not see how to reliably detect
presence of make server.

I think the gcc binary can look for jobserv environment, detect jobserv
and if it is not available remove jobserver option from it prior going
to ld.  I think this works since I think link-time gcc can only be
executed via gcc/g++/gfortran... wrappers.

(unlike lto plugin invoked implicitly for ar/nm etc).

Honza
> 
> As a partial workaround, I wonder if jobserver_active_p couldn't check (with
> fstat/fstat64) if the file descriptors are pipes.  It will still not be 100%
> reliable, as when you are unlucky the file descriptor could be some
> completely unrelated pipe, but at least better than the current state.
> 
> 	Jakub


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