Date:   Fri, 22 Jan 2021 12:25:42 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Willy Tarreau <w@....eu>, valentin.schneider@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/9] tools/nolibc: fix build issues on aarch64 after
 unistd cleanup

On Fri, Jan 22, 2021 at 04:03:26AM -0800, Paul E. McKenney wrote:
> On Thu, Jan 21, 2021 at 11:11:17AM +0000, Mark Rutland wrote:
> 
> [ . . . ]
> 
> > I've given this a spin atop v5.11-rc4, building natively on arm64 on a
> > Debian 10.7 system, and with the whole series applied I'm able to run
> > the rcutorture kvm.sh script without issue (the CONFIG warnings are
> > unrelated to nolibc):
> > 
> > | [mark@...vadlaks:~/src/linux]% ./tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 255 --configs "TREE03"  --kmake-arg "CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64" --duration 1
> > | Creating a statically linked C-language initrd
> > | Done creating a statically linked C-language initrd
> > | Results directory: /home/mark/src/linux/tools/testing/selftests/rcutorture/res/2021.01.21-10.53.24
> > | ./tools/testing/selftests/rcutorture/bin/kvm.sh --cpus 255 --configs TREE03 --kmake-arg CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 --duration 1
> > | ----Start batch 1: Thu 21 Jan 10:53:24 GMT 2021
> > | TREE03 16: Starting build. Thu 21 Jan 10:53:24 GMT 2021
> > | TREE03 16: Waiting for build to complete. Thu 21 Jan 10:53:24 GMT 2021
> > | TREE03 16: Build complete. Thu 21 Jan 10:56:25 GMT 2021
> > | ---- TREE03 16: Kernel present. Thu 21 Jan 10:56:25 GMT 2021
> > | ---- Starting kernels. Thu 21 Jan 10:56:25 GMT 2021
> > | ---- All kernel runs complete. Thu 21 Jan 10:57:35 GMT 2021
> > | ---- TREE03 16: Build/run results:
> > |  --- Thu 21 Jan 10:53:24 GMT 2021: Starting build
> > | :CONFIG_HYPERVISOR_GUEST=y: improperly set
> > | :CONFIG_KVM_GUEST=y: improperly set
> 
> These two (apparently harmless) error messages are due to these lines
> in CFcommon:
> 
> CONFIG_HYPERVISOR_GUEST=y
> CONFIG_KVM_GUEST=y

Yup; I had figured this out, but since this wasn't getting in the way of
actually running the torture tests I had assumed we could deal with that
at some indefinite point in the future, or simply ignore it. ;)

> It looks like CONFIG_HYPERVISOR_GUEST is specific to x86, while KVM_GUEST
> is specific to x86, powerpc, and mips.  (It appears that arm64 doesn't
> need anything here?) 

Yup, we don't need any special options -- arm64 doesn't stricly need any
guest enlightenment to run under a hypervisor, so we never had a need
for KVM_GUEST or HYPERVISOR_GUEST. We have all the common
paravritualized drivers (e.g. virtio) in defconfig too, so that should
all work out of the box.

> Given this variety, I need to make rcutorture know very early on what
> arch it is building for.  My current approach of looking at the
> vmlinux file won't work because I need to get the config right before
> building the kernel.
> 
> One approach would be to look at the initrd/init file, but doing this
> reliably would mean removing the ability for users to supply their own
> initrd file trees.  Another approach would be to look at the current
> environment, perhaps using "uname -m", which will work until someone
> wants to cross-build.  Yet another approach would be to parse the target
> line from the output of "${CROSS_COMPILE}gcc -v".
> 
> Left to myself, I would parse the output of "${CROSS_COMPILE}gcc -v".

Heh, I hadn't considered parsing the target line from that output, and I
guess that works for native builds where "${CROSS_COMPILE}" = "". Neat
trick!

That sounds sensible to me!

Thanks,
Mark.

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