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Date: Fri, 16 Jan 2026 09:35:16 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: Bill Wendling <morbo@google.com>, linux-kernel@vger.kernel.org,
	Kees Cook <kees@kernel.org>, Qing Zhao <qing.zhao@oracle.com>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
	Justin Stitt <justinstitt@google.com>,
	Miguel Ojeda <ojeda@kernel.org>,
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	Heiko Carstens <hca@linux.ibm.com>,
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	Masahiro Yamada <masahiroy@kernel.org>,
	linux-hardening@vger.kernel.org, llvm@lists.linux.dev,
	Jan Hendrik Farr <kernel@jfarr.cc>
Subject: Re: [PATCH v2 1/2] Compiler Attributes: Add __counted_by_ptr macro
Message-ID: <20260116083516.GI830755@noisy.programming.kicks-ass.net>
References: <20251121193957.1655580-2-morbo@google.com>
 <20251121195504.1661783-1-morbo@google.com>
 <CANiq72=kqJApbOJ0hmC_mAYe6DO8YqXSFaLJOsbPhkXfxmvJHQ@mail.gmail.com>
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In-Reply-To: <CANiq72=kqJApbOJ0hmC_mAYe6DO8YqXSFaLJOsbPhkXfxmvJHQ@mail.gmail.com>

On Fri, Nov 21, 2025 at 10:47:45PM +0100, Miguel Ojeda wrote:
> On Fri, Nov 21, 2025 at 8:55 PM Bill Wendling <morbo@google.com> wrote:
> >
> > +/*
> > + * Optional: only supported since clang >= 21
> > + *
> > + * clang: https://github.com/llvm/llvm-project/pull/137250
> > + */
> > +#ifdef CONFIG_CC_HAS_COUNTED_BY_FOR_POINTER
> > +#define __counted_by_ptr(member)       __attribute__((__counted_by__(member)))
> > +#else
> > +#define __counted_by_ptr(member)
> > +#endif
> 
> I guess there is a reason for this name, but it sounds to me a bit
> like the thing between parenthesis is a pointer, i.e. that perhaps it
> is the pointee that one that counts.
> 
> Hmm... what about `__ptr_counted_by`?

Kees promised to drop this attribute once GCC-16 releases by basically
doing 's/__counted_by_ptr/__counted_by/' and unifying things again.

This split out state will only exist for a very short while until GCC
has a release with this feature on.