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From: Willy Tarreau <w@1wt.eu>
To: "Thomas Weißschuh" <linux@weissschuh.net>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] tools/nolibc: use __builtin_offsetof()
Date: Sat, 4 Apr 2026 10:34:24 +0200	[thread overview]
Message-ID: <adDNEEmZrqi-IiYp@1wt.eu> (raw)
In-Reply-To: <20260401-nolibc-asprintf-v1-1-46292313439f@weissschuh.net>

Hi Thomas,

On Wed, Apr 01, 2026 at 05:07:27PM +0200, Thomas Weißschuh wrote:
> The current custom implementation of offsetof() fails UBSAN:
> runtime error: member access within null pointer of type 'struct ...'
> This means that all its users, including container_of(), free() and
> realloc(), fail.
> 
> Use __builtin_offsetof() instead which does not have this issue and
> has been available since GCC 4 and clang 4.

Yeah, that's a place where I find the standard ambiguous and ridiculously
absurd (since there's no dereference, only an address calculations), but I
had to do the same in haproxy recently for the same reasons, and I didn't
remember that we had it in nolibc as well. So that's an obvious ack!

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

thanks,
Willy

  reply	other threads:[~2026-04-04  8:34 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-04-01 15:07 [PATCH 0/3] tools/nolibc: add support for asprintf() Thomas Weißschuh
2026-04-01 15:07 ` [PATCH 1/3] tools/nolibc: use __builtin_offsetof() Thomas Weißschuh
2026-04-04  8:34   ` Willy Tarreau [this message]
2026-04-04 15:29     ` David Laight
2026-04-01 15:07 ` [PATCH 2/3] selftests/nolibc: test the memory allocator Thomas Weißschuh
2026-04-04  8:51   ` Willy Tarreau
2026-04-01 15:07 ` [PATCH 3/3] tools/nolibc: add support for asprintf() Thomas Weißschuh
2026-04-04  8:53   ` Willy Tarreau
2026-04-04 15:34   ` David Laight
2026-04-05 15:39     ` Thomas Weißschuh
2026-04-07 10:46       ` David Laight

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