linux-kernel - Re: [PATCH] arm64/mm: Fix annotated branch unbootable kernel

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Message-ID: <aVwp_BJx84gXHPlD@willie-the-truck>
Date: Mon, 5 Jan 2026 21:15:40 +0000
From: Will Deacon <will@...nel.org>
To: Breno Leitao <leitao@...ian.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Mark Rutland <mark.rutland@....com>,
	Laura Abbott <labbott@...hat.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>, puranjay@...nel.org,
	usamaarif642@...il.com, kernel-team@...a.com,
	stable@...r.kernel.org
Subject: Re: [PATCH] arm64/mm: Fix annotated branch unbootable kernel

On Wed, Dec 31, 2025 at 04:44:05AM -0800, Breno Leitao wrote:
> The arm64 kernel doesn't boot with annotated branches
> (PROFILE_ANNOTATED_BRANCHES) enabled and CONFIG_DEBUG_VIRTUAL together.
> 
> Bisecting it, I found that disabling branch profiling in arch/arm64/mm
> solved the problem. Narrowing down a bit further, I found that
> physaddr.c is the file that needs to have branch profiling disabled to
> get the machine to boot.
> 
> I suspect that it might invoke some ftrace helper very early in the boot
> process and ftrace is still not enabled(!?).
> 
> Disable branch profiling for physaddr.o to allow booting an arm64
> machine with CONFIG_PROFILE_ANNOTATED_BRANCHES and
> CONFIG_DEBUG_VIRTUAL together.
> 
> Cc: stable@...r.kernel.org
> Fixes: ec6d06efb0bac ("arm64: Add support for CONFIG_DEBUG_VIRTUAL")
> Signed-off-by: Breno Leitao <leitao@...ian.org>
> ---
> Another approach is to disable profiling on all arch/arm64 code, similarly to
> x86, where DISABLE_BRANCH_PROFILING is called for all arch/x86 code. See
> commit 2cbb20b008dba ("tracing: Disable branch profiling in noinstr
> code").

Yes, let's start with arch/arm64/. We know that's safe and then if
somebody wants to make it finer-grained, it's on them to figure out a
way to do it without playing whack-a-mole.

Will