Re: [PATCH] kbuild: pass jobserver to cmd_ld_vmlinux.o

[Jiri Slaby]

On 17. 06. 22, 18:32, Nick Desaulniers wrote:
> On Fri, Jun 17, 2022 at 3:35 AM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
> > On Fri, Jun 17, 2022 at 12:53 AM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
> > > On Thu, Jun 16, 2022 at 4:09 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote:
> > > > On Thu, Jun 16, 2022 at 12:45 PM Jiri Slaby <jslaby@xxxxxxx> wrote:
> > > > > Until the link-vmlinux.sh split (cf. the commit below), the linker was
> > > > > run with jobserver set in MAKEFLAGS. After the split, the command in
> > > > > Makefile.vmlinux_o is not prefixed by "+" anymore, so this information
> > > > > is lost.
> > > > >
> > > > > Restore it as linkers working in parallel (esp. the LTO ones) make a use
> > > > > of it.
>
> TBH, I agree with Masahiro. I didn't understand this comment "esp. the
> LTO ones."  Jiri, can you clarify what you mean here?

Sure. clang is not the only compiler/linker that can handle kernel ;). 
So while rebasing gcc-LTO-kernel-patches to 5.19-rc (to upstream them 
later), this broke. See:
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/lto-wrapper.cc;h=26e06e77be4e0afb2bc3e913062a9c51cab5d205;hb=HEAD#l1336

gcc really parses MAKEFLAGS and looks for "--jobserver-auth=" there, if 
one passes specifies -flto=jobserver.

thanks,
--
js
suse labs