linux-kernel - Re: Set environment variable `KVM` makes build fail

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Message-ID: <CAABZP2yOA2n-xux8uUC72vVYc14JfCawoOzp_pnTGDvY8cRSnw@mail.gmail.com>
Date:   Sun, 13 Feb 2022 16:07:55 +0800
From:   Zhouyi Zhou <zhouzhouyi@...il.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        rcu <rcu@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: Set environment variable `KVM` makes build fail

Dear Paul

Thank you for your trust in me.

I think the following patch has a good explanation of what happened ;-)
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/tools/testing/selftests/rcutorture/bin/torture.sh?id=a7d89cfb8e1269cb6d22453adba56b8d0218589f
"The torture-test scripting's long-standing use of KVM as the
environment variable tracking the pathname of the rcutorture directory
now conflicts with allmodconfig builds due to the
virt/kvm/Makefile.kvm file's use of this as a makefile variable"

Thanks
Zhouyi

On Sun, Feb 13, 2022 at 2:03 PM Paul Menzel <pmenzel@...gen.mpg.de> wrote:
>
> Dear Linux folks,
>
>
> Playing with rcutorture
> (`tools/testing/selftests/rcutorture/bin/torture.sh`), a Linux kernel
> build failed, because the script sets and exports the environment
> variable `KVM`. I was able to reproduce that manually (on x86_64):
>
>      $ make defconfig
>      $ scripts/config -m KVM
>      $ scripts/config -m KVM_INTEL
>      $ scripts/config -d KVM_AMD
>      $ scripts/config -d KVM_XEN
>      $ scripts/config -d KVM_MMU_AUDIT
>      $ export KVM=XXX
>      $ make arch/x86/kvm/kvm.o
>      […]
>        LINK    /dev/shm/linux-kvm/tools/objtool/objtool
>      make[2]: *** No rule to make target 'arch/x86/kvm/XXX/kvm_main.o',
> needed by 'arch/x86/kvm/kvm.o'.  Stop.
>      make[1]: *** [scripts/Makefile.build:550: arch/x86/kvm] Error 2
>      make: *** [Makefile:1831: arch/x86] Error 2
>
> The directory `arch/x86/kvm/XXX` is created somehow.
>
> Is that expected? Do you know what is going on? I wasn’t able to
> reproduce this with other variables like `SND_HDA` for example.
>
>
> Kind regards,
>
> Paul