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Date: Wed, 28 Feb 2024 23:51:23 +0200
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Kees Cook <keescook@chromium.org>
Cc: Vinod Koul <vkoul@kernel.org>, Linus Walleij <linus.walleij@linaro.org>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	Mark Brown <broonie@kernel.org>,
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	Jonathan Cameron <jic23@kernel.org>,
	Lars-Peter Clausen <lars@metafoo.de>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>
Subject: Re: [PATCH v4 2/8] overflow: Add struct_size_with_data() and
 struct_data_pointer() helpers
Message-ID: <Zd-q20FkC_3DQ14i@smile.fi.intel.com>
References: <20240228204919.3680786-1-andriy.shevchenko@linux.intel.com>
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 <202402281334.876DC89@keescook>
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On Wed, Feb 28, 2024 at 01:37:36PM -0800, Kees Cook wrote:
> On Wed, Feb 28, 2024 at 10:41:32PM +0200, Andy Shevchenko wrote:

..

> > +#define struct_data_pointer(p, a)	PTR_ALIGN((void *)((p) + 1), (a))
> 
> I'm not super excited about propagating the "p + 1" code pattern to find
> things after an allocation. This leads to the compiler either being
> blind to accesses beyond an allocation, or being too conservative about
> accesses beyond an object. Instead of these helpers I would much prefer
> that data structures that use this code pattern be converted to using
> trailing flexible arrays, at which point the compiler is in a much
> better position to reason about sizes.

There is nothing about flexible arrays in this.
Maybe you have been confused by my choice for name of the macros.
In that case I also can argue that current struct_size() is a good one.
(something like struct_size_with_flex_array() can be more specific)

-- 
With Best Regards,
Andy Shevchenko