Date:   Wed, 28 Jul 2021 00:45:54 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Fangrui Song <maskray@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Christoph Hellwig <hch@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH v2 2/2] Makefile: infer CROSS_COMPILE from SRCARCH for
 LLVM=1 LLVM_IAS=1

On Tue, Jul 27, 2021 at 11:16 PM Eric W. Biederman
<ebiederm@...ssion.com> wrote:
>
> Masahiro Yamada <masahiroy@...nel.org> writes:
>
> > On Tue, Jul 27, 2021 at 5:27 AM Eric W. Biederman <ebiederm@...ssion.com> wrote:
> >>
> >> Masahiro Yamada <masahiroy@...nel.org> writes:
> >>
> >> > On Wed, Jul 21, 2021 at 4:58 AM Arnd Bergmann <arnd@...nel.org> wrote:
> >> >>
> >> >> On Tue, Jul 20, 2021 at 7:43 PM Linus Torvalds
> >> >> <torvalds@...ux-foundation.org> wrote:
> >> >> > On Tue, Jul 20, 2021 at 1:05 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
> >> >> >
> >> >> > We do most of the other heavy lifting in this area in Kconfig anyway,
> >> >> > why not add that compiler choice?
> >> >> >
> >> >> > Obviously it would be gated by the tests to see which compilers are
> >> >> > _installed_ (and that they are valid versions), so that it doesn't ask
> >> >> > stupid things ("do you want gcc or clang" when only one of them is
> >> >> > installed and/or viable).
> >> >>
> >> >> I don't see a good way of making Kconfig options both select the
> >> >> compiler and defining variables based on the compiler, since that
> >> >> would mean teaching Kconfig about re-evaluating all compiler
> >> >> dependent settings whenever the first option changes.
> >> >>
> >> >> I do have another idea that I think would work though.
> >> >>
> >> >> > Hmm? So then any "LLVM=1" thing would be about the "make config"
> >> >> > stage, not the actual build stage.
> >> >> >
> >> >> > (It has annoyed me for years that if you want to cross-compile, you
> >> >> > first have to do "make ARCH=xyz config" and then remember to do "make
> >> >> > ARCH=xyz" for the build too, but I cross-compile so seldom that I've
> >> >> > never really cared).
> >> >>
> >> >> The best thing that I have come up with is a pre-configure step, where
> >> >> an object tree gets seeded with a makefile fragment that gets included
> >> >> for any 'make' invocation. This would set 'ARCH=', 'CROSS_COMPILE',
> >> >> 'CC=' and possibly any other option that gets passed to 'make' as
> >> >> a variable and has to exist before calling 'make *config'.
> >> >
> >> >
> >> > There is no need to add a hook to include such makefile fragment(s).
> >> >
> >> > Quite opposite, you can put your Makefile (in a different filename)
> >> > that includes the top Makefile.
> >> >
> >> >
> >> > I think this is what people are already doing:
> >> >
> >> >
> >> > GNU Make looks for 'GNUmakefile', 'makefile', and 'Makefile'
> >> > in this order.
> >> >
> >> >
> >> > So, you can put 'GNUmakefile' with your favorite setups.
> >> >
> >> >
> >> > $ cat GNUmakefile
> >> > ARCH=arm64
> >> > CROSS_COMPILE=aarch64-linux-gnu-
> >> > CC=clang
> >> > include Makefile
> >>
> >> Very weird.
> >>
> >> I just tested this and it does not work.
> >> I did this:
> >>
> >> $ cat GNUmakefile
> >> ARCH = alpha
> >> CROSS_COMPILE = $(arch-prefix alpha)
> >> include Makefile
> >>
> >> In one of my build directories and the main makefile simply does not see
> >> the value of ARCH or CROSS_COMPILE I set.  I have confirmed that my
> >> GNUmakefile is being read, because everything breaks if I remove the
> >> include line.
> >>
> >> Does anyone have any ideas?
> >>
> >> Something so we don't have to specify all of these variables on the make
> >> command line would be nice.
> >>
> >> Eric
> >
> >
> > Worked for me.
> >
> > Could you tell me the exact steps you did?
> >
> >
> > This is my case:
> >
> > My kernel source tree is located at $HOME/ref/linux
> > alpha tool chains are located at $HOME/tools/alpha-10.1.0/bin
> >
> >
> >
> > I tried a simple GNUmakefile with 3 lines.
> >
> > You can see 'make' is building the alpha kernel
> >
> >
> > Please see below:
>
> Interesting.  That appears to work if I don't specify a build directory.
> Once I specify a build directory with O= it does not work.
>
> When I am working on a change that affects multiple architectures
> I really want a build directory that is not my source tree so I can
> test small changes on multiple architectures without needing to rebuild
> everything.
>
> Eric


Ah, OK.
When you specify O= option, Kbuild will
invoke sub-make.
So you need to add 'export' to the
variables.

Please see the following modified version.





masahiro@...ver:~/ref/linux$ rm -rf build-dir/
masahiro@...ver:~/ref/linux$ cat GNUmakefile
export ARCH = alpha
export CROSS_COMPILE = $(HOME)/tools/alpha-10.1.0/bin/alpha-linux-
include Makefile
masahiro@...ver:~/ref/linux$ make O=build-dir defconfig
make[1]: Entering directory '/home/masahiro/ref/linux/build-dir'
  GEN     Makefile
  HOSTCC  scripts/basic/fixdep
  HOSTCC  scripts/kconfig/conf.o
  HOSTCC  scripts/kconfig/confdata.o
  HOSTCC  scripts/kconfig/expr.o
  LEX     scripts/kconfig/lexer.lex.c
  YACC    scripts/kconfig/parser.tab.[ch]
  HOSTCC  scripts/kconfig/lexer.lex.o
  HOSTCC  scripts/kconfig/menu.o
  HOSTCC  scripts/kconfig/parser.tab.o
  HOSTCC  scripts/kconfig/preprocess.o
  HOSTCC  scripts/kconfig/symbol.o
  HOSTCC  scripts/kconfig/util.o
  HOSTLD  scripts/kconfig/conf
*** Default configuration is based on 'defconfig'
#
# configuration written to .config
#
make[1]: Leaving directory '/home/masahiro/ref/linux/build-dir'
masahiro@...ver:~/ref/linux$ make O=build-dir
make[1]: Entering directory '/home/masahiro/ref/linux/build-dir'
  GEN     Makefile
  SYSHDR  arch/alpha/include/generated/uapi/asm/unistd_32.h
  SYSTBL  arch/alpha/include/generated/asm/syscall_table.h
  HOSTCC  scripts/kallsyms
  WRAP    arch/alpha/include/generated/uapi/asm/bpf_perf_event.h
  WRAP    arch/alpha/include/generated/uapi/asm/ipcbuf.h
  WRAP    arch/alpha/include/generated/uapi/asm/msgbuf.h
  WRAP    arch/alpha/include/generated/uapi/asm/poll.h
  WRAP    arch/alpha/include/generated/uapi/asm/sembuf.h
  WRAP    arch/alpha/include/generated/uapi/asm/shmbuf.h
  WRAP    arch/alpha/include/generated/asm/export.h
  WRAP    arch/alpha/include/generated/asm/kvm_para.h
  WRAP    arch/alpha/include/generated/asm/mcs_spinlock.h
  WRAP    arch/alpha/include/generated/asm/compat.h
  WRAP    arch/alpha/include/generated/asm/current.h
  WRAP    arch/alpha/include/generated/asm/exec.h
  WRAP    arch/alpha/include/generated/asm/fb.h
  WRAP    arch/alpha/include/generated/asm/irq_work.h
  WRAP    arch/alpha/include/generated/asm/kmap_size.h
  WRAP    arch/alpha/include/generated/asm/kprobes.h
  WRAP    arch/alpha/include/generated/asm/local64.h
  WRAP    arch/alpha/include/generated/asm/mmiowb.h
  WRAP    arch/alpha/include/generated/asm/module.lds.h
  WRAP    arch/alpha/include/generated/asm/msi.h
  WRAP    arch/alpha/include/generated/asm/preempt.h
  WRAP    arch/alpha/include/generated/asm/sections.h
  WRAP    arch/alpha/include/generated/asm/simd.h
  WRAP    arch/alpha/include/generated/asm/softirq_stack.h
  WRAP    arch/alpha/include/generated/asm/trace_clock.h
  WRAP    arch/alpha/include/generated/asm/unaligned.h
  WRAP    arch/alpha/include/generated/asm/vermagic.h
  UPD     include/config/kernel.release
  UPD     include/generated/uapi/linux/version.h
  UPD     include/generated/utsrelease.h
  CC      scripts/mod/empty.o
  HOSTCC  scripts/mod/mk_elfconfig
  MKELF   scripts/mod/elfconfig.h
  HOSTCC  scripts/mod/modpost.o
  CC      scripts/mod/devicetable-offsets.s
  UPD     scripts/mod/devicetable-offsets.h
  HOSTCC  scripts/mod/file2alias.o
  HOSTCC  scripts/mod/sumversion.o
  HOSTLD  scripts/mod/modpost
  CC      kernel/bounds.s
  UPD     include/generated/bounds.h
  UPD     include/generated/timeconst.h
  CC      arch/alpha/kernel/asm-offsets.s
  UPD     include/generated/asm-offsets.h
  CALL    ../scripts/checksyscalls.sh
<stdin>:1515:2: warning: #warning syscall clone3 not implemented [-Wcpp]
  CALL    ../scripts/atomic/check-atomics.sh
  CC      init/main.o
  CHK     include/generated/compile.h
  UPD     include/generated/compile.h
  CC      init/version.o
  CC      init/do_mounts.o
  CC      init/noinitramfs.o
  CC      init/calibrate.o
  CC      init/init_task.o
  AR      init/built-in.a
  AR      usr/built-in.a
  AS      arch/alpha/kernel/head.o
  LDS     arch/alpha/kernel/vmlinux.lds
  AS      arch/alpha/kernel/entry.o
  CC      arch/alpha/kernel/traps.o
  CC      arch/alpha/kernel/process.o
  CC      arch/alpha/kernel/osf_sys.o
  CC      arch/alpha/kernel/irq.o
  CC      arch/alpha/kernel/irq_alpha.o
  CC      arch/alpha/kernel/signal.o
  CC      arch/alpha/kernel/setup.o
  CC      arch/alpha/kernel/ptrace.o
  CC      arch/alpha/kernel/time.o
  AS      arch/alpha/kernel/systbls.o
  CC      arch/alpha/kernel/err_common.o
  CC      arch/alpha/kernel/io.o
  CC      arch/alpha/kernel/bugs.o
  CC      arch/alpha/kernel/console.o
  CC      arch/alpha/kernel/pci.o
  CC      arch/alpha/kernel/pci_iommu.o
  CC      arch/alpha/kernel/pci-sysfs.o
  CC      arch/alpha/kernel/module.o
  CC      arch/alpha/kernel/rtc.o
  CC      arch/alpha/kernel/core_apecs.o
  CC      arch/alpha/kernel/core_cia.o
  CC      arch/alpha/kernel/core_irongate.o
  CC      arch/alpha/kernel/core_lca.o
  CC      arch/alpha/kernel/core_mcpcia.o
  CC      arch/alpha/kernel/core_polaris.o
  CC      arch/alpha/kernel/core_t2.o
  CC      arch/alpha/kernel/core_tsunami.o
  CC      arch/alpha/kernel/sys_alcor.o
  CC      arch/alpha/kernel/sys_cabriolet.o
  CC      arch/alpha/kernel/sys_dp264.o
  CC      arch/alpha/kernel/sys_eb64p.o
  CC      arch/alpha/kernel/sys_eiger.o
  CC      arch/alpha/kernel/sys_jensen.o
  CC      arch/alpha/kernel/sys_miata.o
  CC      arch/alpha/kernel/sys_mikasa.o
  CC      arch/alpha/kernel/sys_nautilus.o
  CC      arch/alpha/kernel/sys_noritake.o
  CC      arch/alpha/kernel/sys_rawhide.o
  CC      arch/alpha/kernel/sys_ruffian.o
  CC      arch/alpha/kernel/sys_rx164.o
  CC      arch/alpha/kernel/sys_sable.o
  CC      arch/alpha/kernel/sys_sio.o
  CC      arch/alpha/kernel/sys_sx164.o
  CC      arch/alpha/kernel/sys_takara.o
  CC      arch/alpha/kernel/irq_pyxis.o
  CC      arch/alpha/kernel/irq_i8259.o
  CC      arch/alpha/kernel/irq_srm.o
  CC      arch/alpha/kernel/err_ev6.o
  CC      arch/alpha/kernel/es1888.o
  CC      arch/alpha/kernel/smc37c669.o
  CC      arch/alpha/kernel/smc37c93x.o
  CC      arch/alpha/kernel/pc873xx.o
  CC      arch/alpha/kernel/gct.o
  CC      arch/alpha/kernel/srmcons.o
  AR      arch/alpha/kernel/built-in.a
  CC [M]  arch/alpha/kernel/srm_env.o
  CC      arch/alpha/mm/init.o
  CC      arch/alpha/mm/fault.o
  AR      arch/alpha/mm/built-in.a
  CC      arch/alpha/math-emu/math.o
  AS      arch/alpha/math-emu/qrnnd.o
  AR      arch/alpha/math-emu/built-in.a
  AR      arch/alpha/built-in.a
  CC      kernel/sched/core.o
  CC      kernel/sched/loadavg.o
  CC      kernel/sched/clock.o
  CC      kernel/sched/cputime.o
  CC      kernel/sched/idle.o
  CC      kernel/sched/fair.o
  CC      kernel/sched/rt.o
  CC      kernel/sched/deadline.o
  CC      kernel/sched/wait.o
  CC      kernel/sched/wait_bit.o
  CC      kernel/sched/swait.o
  CC      kernel/sched/completion.o
  CC      kernel/sched/debug.o
  CC      kernel/sched/membarrier.o
  AR      kernel/sched/built-in.a
  CC      kernel/locking/mutex.o
  CC      kernel/locking/semaphore.o
  CC      kernel/locking/rwsem.o
  CC      kernel/locking/percpu-rwsem.o
  CC      kernel/locking/rtmutex.o
  AR      kernel/locking/built-in.a
  CC      kernel/power/qos.o
  CC      kernel/power/poweroff.o
  AR      kernel/power/built-in.a
  CC      kernel/printk/printk.o
  CC      kernel/printk/printk_safe.o
  CC      kernel/printk/printk_ringbuffer.o
  AR      kernel/printk/built-in.a
  CC      kernel/irq/irqdesc.o
  CC      kernel/irq/handle.o
  CC      kernel/irq/manage.o
  CC      kernel/irq/spurious.o
  CC      kernel/irq/resend.o
  CC      kernel/irq/chip.o
  CC      kernel/irq/dummychip.o
  CC      kernel/irq/devres.o
  CC      kernel/irq/autoprobe.o
  CC      kernel/irq/proc.o
  AR      kernel/irq/built-in.a
  CC      kernel/rcu/update.o
  CC      kernel/rcu/sync.o
  CC      kernel/rcu/srcutiny.o
  CC      kernel/rcu/tiny.o
  AR      kernel/rcu/built-in.a
  AR      kernel/livepatch/built-in.a
  CC      kernel/dma/mapping.o
  CC      kernel/dma/direct.o
  CC      kernel/dma/ops_helpers.o
  CC      kernel/dma/dummy.o
  AR      kernel/dma/built-in.a
  AR      kernel/entry/built-in.a
  CC      kernel/time/time.o
  CC      kernel/time/timer.o
  CC      kernel/time/hrtimer.o
  CC      kernel/time/timekeeping.o
  CC      kernel/time/ntp.o
  CC      kernel/time/clocksource.o
  CC      kernel/time/jiffies.o
  CC      kernel/time/timer_list.o
  CC      kernel/time/timeconv.o
  CC      kernel/time/timecounter.o
  CC      kernel/time/alarmtimer.o
  CC      kernel/time/posix-timers.o
  CC      kernel/time/posix-cpu-timers.o
  CC      kernel/time/posix-clock.o
  CC      kernel/time/itimer.o
  CC      kernel/time/clockevents.o
  CC      kernel/time/tick-common.o
  AR      kernel/time/built-in.a
  CC      kernel/bpf/core.o
  AR      kernel/bpf/built-in.a




-- 
Best Regards
Masahiro Yamada

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