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Date: Sat, 19 Apr 2025 12:11:35 +0200
From: Thomas =?utf-8?Q?Wei=C3=9Fschuh?= <linux@weissschuh.net>
To: Willy Tarreau <w@1wt.eu>
Cc: "Paul E. McKenney" <paulmck@kernel.org>, Shuah Khan <shuah@kernel.org>, 
	linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 3/6] tools/nolibc: properly align dirent buffer
Message-ID: <7ce6cd20-e20a-4bfa-b893-995ce6585d03@t-8ch.de>
References: <20250416-nolibc-ubsan-v1-0-c4704bb23da7@weissschuh.net>
 <20250416-nolibc-ubsan-v1-3-c4704bb23da7@weissschuh.net>
 <20250419091140.GC31874@1wt.eu>
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In-Reply-To: <20250419091140.GC31874@1wt.eu>

On 2025-04-19 11:11:40+0200, Willy Tarreau wrote:
> On Wed, Apr 16, 2025 at 08:40:18PM +0200, Thomas Weißschuh wrote:
> > As byte buffer is overlaid with a 'struct dirent64'.
> > it has to satisfy the structs alignment requirements.
> > 
> > Fixes: 665fa8dea90d ("tools/nolibc: add support for directory access")
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> 
> Oh good catch! I already faced crashes in other programs due to AVX
> memcpy when doing similar casts without thinking about alignment.
> 
> > @@ -58,6 +58,7 @@ int closedir(DIR *dirp)
> >  static __attribute__((unused))
> >  int readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result)
> >  {
> > +	__attribute__((aligned(__alignof__(struct linux_dirent64))))
> >  	char buf[sizeof(struct linux_dirent64) + NAME_MAX + 1];
> 
> I tend to find it more readable when the attribute is on the same line as
> the type on variables declaration, often at the end of the line, to keep
> declarations alignes, even if that makes longer lines. If alignment concerns
> come back often, we could maybe have __nolibc_align(<align>) and maybe even
> __nolibc_align_as(<type>) to slightly shorten the lines. Just an idea.

Sounds good, the attribute soup is annoying.

> In any case: Acked-by: Willy Tarreau <w@1wt.eu>

Thanks!


Thomas