linux-kernel - Re: [PATCH bpf-next v2 8/9] selftests/bpf: Add selftests for load-acquire and store-release instructions

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Message-ID: <6a87b140203461f9d56874b9e4a778febdcd47a6.camel@gmail.com>
Date: Mon, 10 Feb 2025 16:20:18 -0800
From: Eduard Zingerman <eddyz87@...il.com>
To: Peilin Ye <yepeilin@...gle.com>, bpf@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org
Cc: bpf@...f.org, Xu Kuohai <xukuohai@...weicloud.com>, David Vernet	
 <void@...ifault.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann	
 <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai
 Lau	 <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, Yonghong Song	
 <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, KP
 Singh	 <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo	
 <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, Jonathan Corbet	
 <corbet@....net>, "Paul E. McKenney" <paulmck@...nel.org>, Puranjay Mohan	
 <puranjay@...nel.org>, Ilya Leoshkevich <iii@...ux.ibm.com>, Heiko Carstens
	 <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>, Catalin Marinas	
 <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Quentin Monnet	
 <qmo@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan
 <shuah@...nel.org>,  Ihor Solodrai <ihor.solodrai@...ux.dev>, Yingchi Long
 <longyingchi24s@....ac.cn>, Josh Don <joshdon@...gle.com>,  Barret Rhoden
 <brho@...gle.com>, Neel Natu <neelnatu@...gle.com>, Benjamin Segall
 <bsegall@...gle.com>, 	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 8/9] selftests/bpf: Add selftests for
 load-acquire and store-release instructions

On Sat, 2025-02-08 at 02:20 +0000, Peilin Ye wrote:

[...]

> Sorry, that wasn't very accurate - we need to make sure there are no
> "holes" in the .addr_space.1 ELF section, e.g.:
> 
>   /* 8-byte-aligned */
>   __u8 __arena_global load_acquire8_value = 0x12;
>   /* 1-byte hole, causing clang-17 to crash */
>   __u16 __arena_global load_acquire16_value = 0x1234;
> 
> LLVM commit f27c4903c43b ("MC: Add .data. and .rodata. prefixes to
> MCContext section classification") fixed this issue.

This is a bit strange, from commit log it looks like LLVM-17 should
include this commit. But in any case, targeting LLVM >= 18 seems
reasonable to me, the main goal is to have these tests run by CI for
some compiler version.

> - - -
> For now, I think I should:
> 
>   1. change existing #if guards to
>      "#if defined(__TARGET_ARCH_arm64) && __clang_major__ >= 18"
> 
>   2. additionally, guard "__arena_global" variable definitions behind
>      "#if __clang_major >= 18" so that clang-17 doesn't try to compile
>      that part (then crash)
> 
> Will fix in v3.
> 
> Thanks,
> Peilin Ye
>