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Date: Sun, 27 Sep 2026 14:05:38 +0000
From: "Jose Fernandez (Anthropic)" <jose.fernandez@linux.dev>
To: Bill Wendling <morbo@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>, 
	Masami Hiramatsu <mhiramat@kernel.org>, Mark Rutland <mark.rutland@arm.com>, 
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Nathan Chancellor <nathan@kernel.org>, 
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	Eduard Zingerman <eddyz87@gmail.com>, Kumar Kartikeya Dwivedi <memxor@gmail.com>, 
	Martin KaFai Lau <martin.lau@linux.dev>, Song Liu <song@kernel.org>, 
	Yonghong Song <yonghong.song@linux.dev>, Jiri Olsa <jolsa@kernel.org>, 
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	Tamir Duberstein <tamird@kernel.org>, Alexandre Courbot <acourbot@nvidia.com>, 
	Onur =?utf-8?B?w5Z6a2Fu?= <work@onurozkan.dev>, Sami Tolvanen <samitolvanen@google.com>, 
	Kees Cook <kees@kernel.org>, Leon Hwang <leon.hwang@linux.dev>, 
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	Ben Cressey <ben@cressey.dev>, "Florent Revest (Anthropic)" <florent.revest@linux.dev>
Subject: Re: [PATCH v2 6/9] arm64: cfi: Use CONFIG_ARM64_FUNCTION_PREFIX_NOPS
 for the type hash offset
Message-ID: <arkimpxRmauCfcn8@linux.dev>
References: <20260924-b4-arm64-callops-kcfi-v2-0-587865b6d991@linux.dev>
 <20260924-b4-arm64-callops-kcfi-v2-6-587865b6d991@linux.dev>
 <CAGG=3QVs=e5JtAs-D98vDsj2ax9H0gH-_rPc0oKhx-vNpq_RyQ@mail.gmail.com>
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In-Reply-To: <CAGG=3QVs=e5JtAs-D98vDsj2ax9H0gH-_rPc0oKhx-vNpq_RyQ@mail.gmail.com>

On Fri, Sep 25, 2026 at 12:17 PM Bill Wendling wrote:
> > +       return 4 + 4 * CONFIG_ARM64_FUNCTION_PREFIX_NOPS;
>
> *drive by review* Could you explain the two fours in this equation
> with a comment? (Feel free to ignore this if it's obvious to
> developers.)

The first is the type hash and the second is the size of a NOP. For v3
I'll spell the second one out and add a comment for the first.

	/* The 4-byte type hash sits before the prefix NOPs. */
	return 4 + CONFIG_ARM64_FUNCTION_PREFIX_NOPS * AARCH64_INSN_SIZE;

- Jose