linux-kernel - Re: include/linux/build_bug.h:78:41: error: static assertion failed: "struct bpf_fib

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Message-ID: <CAPyNcWeXpidnVsXgt4XpwXiA0CRFdZYFN9O2ys5oq9FQKXNxsw@mail.gmail.com>
Date: Wed, 3 Apr 2024 11:57:07 +0200
From: Anton Protopopov <aspsk@...valent.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
Cc: Arnd Bergmann <arnd@...db.de>, Naresh Kamboju <naresh.kamboju@...aro.org>, 
	open list <linux-kernel@...r.kernel.org>, lkft-triage@...ts.linaro.org, 
	Linux Regressions <regressions@...ts.linux.dev>, Anders Roxell <anders.roxell@...aro.org>, 
	Dan Carpenter <dan.carpenter@...aro.org>, Daniel Borkmann <daniel@...earbox.net>, 
	David Ahern <dsahern@...nel.org>, Alexei Starovoitov <ast@...nel.org>, 
	Russell King <rmk+kernel@...linux.org.uk>, Ard Biesheuvel <ardb@...nel.org>, 
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: include/linux/build_bug.h:78:41: error: static assertion failed:
 "struct bpf_fib_lookup size check"

On Wed, Apr 3, 2024 at 11:39 AM Alexander Lobakin
<aleksander.lobakin@...el.com> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
> 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@...aro.org> 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@...aro.org>
> >>>
> >>> 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.

Yeah, I am sending a patch for this right now. Better not to depend on
compiler options