Re: include/linux/build_bug.h:78:41: error: static assertion failed: "struct bpf_fib_lookup size check"

[Alexander Lobakin]

From: Arnd Bergmann <arnd@xxxxxxxx>
Date: Wed, 03 Apr 2024 10:45:36 +0200

> On Wed, Apr 3, 2024, at 10:10, Anton Protopopov wrote:
>> On Wed, Apr 3, 2024 at 10:03 AM Naresh Kamboju
>> <naresh.kamboju@xxxxxxxxxx> wrote:
>>>
>>> The arm footbridge_defconfig failed with gcc-13 and gcc-8 on Linux next
>>> starting from next-20240328..next-20240402.
>>>
>>> arm:
>>>   build:
>>>     * gcc-8-footbridge_defconfig - Failed
>>>     * gcc-13-footbridge_defconfig - Failed
>>>
>>> Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>
>>>
>>> In file included from include/linux/bitfield.h:10,
>>>                  from arch/arm/include/asm/ptrace.h:13,
>>>                  from arch/arm/include/asm/processor.h:14,
>>>                  from include/linux/prefetch.h:15,
>>>                  from arch/arm/include/asm/atomic.h:12,
>>>                  from include/linux/atomic.h:7,
>>>                  from net/core/filter.c:20:
>>> include/linux/build_bug.h:78:41: error: static assertion failed:
>>> "struct bpf_fib_lookup size check"
>>>    78 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg)
>>>       |                                         ^~~~~~~~~~~~~~
>>
>> Thanks, I will take a look today

Naresh,

Could you please remove that static_assert() and dump bpf_bif_lookup
layout from pahole?

Anton unionized { smac, dmac } with __u32 mark. On x86_64, the offset of
smac was 52 (aligned to 4) already, so I don't really get what AEABI
does here. IIRC it aligns every structure to 8 bytes?

Maybe we could just add __attribute__((__packed__))
__attribute__((__aligned__(4))) to that anonymous union at the end.

> 
> The problem is CONFIG_AEABI=n, which changes the alignment
> of sub-word struct members. I had assumed that AEABI is enabled
> by default for everything already, but it looks like footbridge
> and a couple of other defconfigs still have it turned off:
> 
> $ git grep -l  CONFIG_ARCH_MULTI_V7.is.not arch/arm/configs/* | xargs git grep -L AEABI
> arch/arm/configs/assabet_defconfig
> arch/arm/configs/collie_defconfig
> arch/arm/configs/footbridge_defconfig
> arch/arm/configs/h3600_defconfig
> arch/arm/configs/jornada720_defconfig
> arch/arm/configs/neponset_defconfig
> arch/arm/configs/netwinder_defconfig
> arch/arm/configs/rpc_defconfig
> arch/arm/configs/spear3xx_defconfig
> arch/arm/configs/spear6xx_defconfig
> arch/arm/configs/spitz_defconfig
> 
> Russell still has machines with an OABI toolchain, but I'm not
> aware of anyone else relying on it. It does cause other
> problems as well, so I already turned it off a long time ago
> for my randconfig testing.
> 
> We should probably make it the default for everything, except
> whichever defconfig Russell uses:
> 
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1159,7 +1159,7 @@ config ARM_PATCH_IDIV
>  config AEABI
>         bool "Use the ARM EABI to compile the kernel" if !CPU_V7 && \
>                 !CPU_V7M && !CPU_V6 && !CPU_V6K && !CC_IS_CLANG && !COMPILE_TEST
> -       default CPU_V7 || CPU_V7M || CPU_V6 || CPU_V6K || CC_IS_CLANG || COMPILE_TEST
> +       default y
>         help
>           This option allows for the kernel to be compiled using the latest
>           ARM ABI (aka EABI).  This is only useful if you are using a user
> 
> Or we could go one step further and make it 'depends on
> EXPERT', short of removing it entirely.>
>      Arnd

Thanks,
Olek