netdev - Re: arch: arm: bpf: Converting cBPF to eBPF for arm 32 bit

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Date:   Tue, 23 May 2017 09:04:40 +0530
From:   Shubham Bansal <illusionist.neo@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Network Development <netdev@...r.kernel.org>, ast@...com,
        Mircea Gherzan <mgherzan@...il.com>,
        David Miller <davem@...emloft.net>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>, nschichan@...ebox.fr,
        andrew@...n.ch
Subject: Re: arch: arm: bpf: Converting cBPF to eBPF for arm 32 bit

Hi Florian,

>> I think it is fine to only target ARMv7. It is harder and harder to
>> find devices on v5 or v6 CPUs that would want to be using BPF JIT,
>> IMO.
>
> There are still a ton of Marvell-based routers out there (e.g: Kirkwood,
> Orion5x) that are ARMv5 and that prompted Nicholas (hey there) to fix
> the cBPF JIT a while ago. I don't think you can just ignore those, it's
> fine not to target them initially, but arguably, QEMU has decent support
> for some ARMv5 platforms that could be used for testing as well
> (realview-eb, versatileab/pbm.

I am using busybox to get the rootfs. Here is what I am doing :-

1. ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make -j4 (for kernel
build as well as busybox build)
2. qemu-system-arm -M vexpress-a9 -dtb
./linux/arch/arm/boot/dts/versatile-ab.dts -kernel ./linux/arch/a
rm/boot/zImage -append "root=/dev/mmcblk0 console=ttyAMA0" -sd
./a9rootfs.ext3 --nographic

Can you help me with running qemu for ARMv5 and ARMv6 ?

>> When they "disappear", it's because there isn't a prerequisite met. I
>> either read the Kconfig files or use "make menuconfig" and "search" to
>> tell me where a config is defined and what is needed to meet the
>> prerequisites.
>>
>> In the case of CPU_BIG_ENDIAN, you need ARCH_SUPPORTS_BIG_ENDIAN,
>> which appears to be only ARCH_IXP4XX. I don't think you're going to
>> find an emulator that will handle this, so I'd suggest ignoring this
>> config for now unless you can find someone with that hardware that you
>> can work with to test it.
>>
>> In the case of CONFIG_FRAME_POINTER, I assume you built a
>> THUMB2_KERNEL? I'd read the notes in arch/arm/Kconfig.debug for
>> 'config FRAME_POINTER'.
>
> It sounds like we are at the point where Shubham's patches should be
> posted so people could test/fix on earlier ARM devices for instance.
>
I would post them as soon as I test them on ARMv5 and ARMv6. If you
can help me with that, please let me know.

> Thanks
> --
> Florian

-Shubham