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

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Message-Id: <20251231-annotated-v1-1-9db1c0d03062@debian.org>
Date: Wed, 31 Dec 2025 04:44:05 -0800
From: Breno Leitao <leitao@...ian.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, 
 Laura Abbott <labbott@...hat.com>
Cc: 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, 
 Breno Leitao <leitao@...ian.org>
Subject: [PATCH] arm64/mm: Fix annotated branch unbootable kernel

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").
---
 arch/arm64/mm/Makefile | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile
index c26489cf96cd..8bfe2451ea26 100644
--- a/arch/arm64/mm/Makefile
+++ b/arch/arm64/mm/Makefile
@@ -14,5 +14,10 @@ obj-$(CONFIG_ARM64_MTE)		+= mteswap.o
 obj-$(CONFIG_ARM64_GCS)		+= gcs.o
 KASAN_SANITIZE_physaddr.o	+= n
 
+# Branch profiling isn't noinstr-safe
+ifdef CONFIG_TRACE_BRANCH_PROFILING
+CFLAGS_physaddr.o += -DDISABLE_BRANCH_PROFILING
+endif
+
 obj-$(CONFIG_KASAN)		+= kasan_init.o
 KASAN_SANITIZE_kasan_init.o	:= n

---
base-commit: c8ebd433459bcbf068682b09544e830acd7ed222
change-id: 20251231-annotated-75de3f33cd7b

Best regards,
--  
Breno Leitao <leitao@...ian.org>