linux-kernel - [PATCH v9 01/32] dyndbg: fix NULL ptr on i386 due to section alignment

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Message-ID: <20260129072932.2190803-2-jim.cromie@gmail.com>
Date: Thu, 29 Jan 2026 00:28:47 -0700
From: Jim Cromie <jim.cromie@...il.com>
To: gregkh@...uxfoundation.org
Cc: Jim Cromie <jim.cromie@...il.com>,
	Jason Baron <jbaron@...mai.com>,
	Łukasz Bartosik <ukaszb@...omium.org>,
	Louis Chauvet <louis.chauvet@...tlin.com>,
	Bagas Sanjaya <bagasdotme@...il.com>,
	Dave Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	dri-devel@...ts.freedesktop.org,
	Petr Mladek <pmladek@...e.com>,
	Shuah Khan <skhan@...uxfoundation.org>,
	linux-doc@...r.kernel.org,
	kernel test robot <oliver.sang@...el.com>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v9 01/32] dyndbg: fix NULL ptr on i386 due to section alignment

When dyndbg classmaps get used (later in this series), the
__dyndbg_classes section (which has 28 byte structs on i386), causes
mis-alignment of the following __dyndbg section, resulting in a NULL
pointer deref in dynamic_debug_init().

To fix this, employ belt + suspenders:

1. move __dyndbg section above __dyndbg_classes.  This restores it to
its original position directly after the ALIGN(8), and fixes the
immediate problem.

2. add ALIGN(8) to the BOUNDED_SECTION* macros.  This aligns all
existing sections using the macro, and also fixes a future
dyndbg_class_* addition which would suffer the same misalignment on
i386.  Many of the existing macro uses already have a preceding ALIGN,
these are now redundant, but are harmless, so are left to avoid churn.

3. remove BOUNDED_SECTION* uses in ORC_UNWINDER sections.  These have
smaller alignments, *and* scripts/sorttable.c does not tolerate the
added ALIGN(8) padding.

Reported-by: kernel test robot <oliver.sang@...el.com>
Closes: https://lore.kernel.org/oe-lkp/202601211325.7e1f336-lkp@intel.com
Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 include/asm-generic/vmlinux.lds.h | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 8ca130af301f..4b4d2773aa22 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -212,11 +212,13 @@
 #endif
 
 #define BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_)	\
+	. = ALIGN(8);							\
 	_BEGIN_##_label_ = .;						\
 	KEEP(*(_sec_))							\
 	_END_##_label_ = .;
 
 #define BOUNDED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_)	\
+	. = ALIGN(8);							\
 	_label_##_BEGIN_ = .;						\
 	KEEP(*(_sec_))							\
 	_label_##_END_ = .;
@@ -383,8 +385,8 @@
 	*(__tracepoints)						\
 	/* implement dynamic printk debug */				\
 	. = ALIGN(8);							\
-	BOUNDED_SECTION_BY(__dyndbg_classes, ___dyndbg_classes)		\
 	BOUNDED_SECTION_BY(__dyndbg, ___dyndbg)				\
+	BOUNDED_SECTION_BY(__dyndbg_classes, ___dyndbg_classes)		\
 	CODETAG_SECTIONS()						\
 	LIKELY_PROFILE()		       				\
 	BRANCH_PROFILE()						\
@@ -867,15 +869,21 @@
 #ifdef CONFIG_UNWINDER_ORC
 #define ORC_UNWIND_TABLE						\
 	.orc_header : AT(ADDR(.orc_header) - LOAD_OFFSET) {		\
-		BOUNDED_SECTION_BY(.orc_header, _orc_header)		\
+		__start_orc_header = .;					\
+		KEEP(*(.orc_header))					\
+		__stop_orc_header = .;					\
 	}								\
 	. = ALIGN(4);							\
 	.orc_unwind_ip : AT(ADDR(.orc_unwind_ip) - LOAD_OFFSET) {	\
-		BOUNDED_SECTION_BY(.orc_unwind_ip, _orc_unwind_ip)	\
+		__start_orc_unwind_ip = .;				\
+		KEEP(*(.orc_unwind_ip))					\
+		__stop_orc_unwind_ip = .;				\
 	}								\
 	. = ALIGN(2);							\
 	.orc_unwind : AT(ADDR(.orc_unwind) - LOAD_OFFSET) {		\
-		BOUNDED_SECTION_BY(.orc_unwind, _orc_unwind)		\
+		__start_orc_unwind = .;					\
+		KEEP(*(.orc_unwind))					\
+		__stop_orc_unwind = .;					\
 	}								\
 	text_size = _etext - _stext;					\
 	. = ALIGN(4);							\
-- 
2.52.0