[PATCH v4 0/5] fix section alignment on i386 when CONFIG_DRM_USE_DYNAMIC_DEBUG=Y

[PATCH v4 0/5] fix section alignment on i386 when CONFIG_DRM_USE_DYNAMIC_DEBUG=Y

[Jim Cromie]

This fixes a section misalignement on i386, when CONFIG_DRM=y and
CONFIG_DRM_USE_DYNAMIC_DEBUG=Y

In this config, the __dyndbg_classes section gets a single
struct/record.  On i386 this is 28-bytes, breaking the required
ALIGN(8) on the following __dyndbg section.

This breaks dynamic_debug_init() with a NULL pointer dereference; the
section traversal logic encounters padding bytes instead of a valid
descriptor.

the series:

1. moves BOUNDED_SECTION_* macros from vmlinux.lds.h to its own file.
   v2- adds note that macros are for vmlinux.lds.h only, not for modules.

2. drops unused HEADERED_SECTION_* macros from that new file

3. adds ALIGN(8) into BOUNDED_SECTION* macros
   omission causing NULL ptr on i386
   adds,uses BOUNDED_SECTION _ALIGNED variants

4. removes now redundant ALIGN(8)s in vmlinux.lds.h

5. adds dyndbg.lds.S to KEEP sections in modules
   follows codetag.lds.h model

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
v3:
- move #includes to top of files,
- drop redundant ALIGN(8) in dydnbg.lds.S: DYNDBG_SECTIONS macro
- add Reviewed-by tag (thx Petr)

v2:
- avoid BOUNDED_SECTION in modules, dont need _start & _end symbols.
- sets 0 address to the sections, not just whatever current is.

---
Jim Cromie (5):
      vmlinux.lds.h: refactor BOUNDED_SECTION_* macros into bounded_sections.lds.h
      vmlinux.lds.h: drop unused HEADERED_SECTION* macros
      vmlinux.lds.h: Fix ALIGN(8) omission causing NULL ptr on i386
      vmlinux.lds.h: remove redundant ALIGN(8) directives
      dyndbg.lds.S: fix lost dyndbg sections in modules

 MAINTAINERS                                |  1 +
 include/asm-generic/bounded_sections.lds.h | 32 ++++++++++++++
 include/asm-generic/dyndbg.lds.h           | 18 ++++++++
 include/asm-generic/vmlinux.lds.h          | 68 ++++++------------------------
 scripts/module.lds.S                       |  2 +
 5 files changed, 66 insertions(+), 55 deletions(-)
---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260630-fix-align-589738662161

Best regards,
-- 
Jim Cromie <jim.cromie@gmail.com>

[PATCH v4 1/5] vmlinux.lds.h: refactor BOUNDED_SECTION_* macros into bounded_sections.lds.h

[Jim Cromie]

Move BOUNDED_SECTION_* macros to a new helper file:
include/asm-generic/bounded_sections.lds.h and include it back into
vmlinux.lds.h.  This allows its reuse later to fix a failure to keep
dyndbg sections in some circumstances.

NOTES:

These macros are only for use in vmlinux.lds.h, where the _start &
_end symbols are needed.  Modules keep sections separate in ELF
sections, with their boundaries known, so the _start and _end are not
useful, and may confuse tools not expecting them.

This patch ignores a checkpatch warning, because new file is covered
by "GENERIC INCLUDE/ASM HEADER FILES" in MAINTAINERS

CC: Arnd Bergmann <arnd@arndb.de>
CC: linux-arch@vger.kernel.org
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
v3: move include to top
---
 include/asm-generic/bounded_sections.lds.h | 36 ++++++++++++++++++++++++++++++
 include/asm-generic/vmlinux.lds.h          | 31 +------------------------
 2 files changed, 37 insertions(+), 30 deletions(-)

diff --git a/include/asm-generic/bounded_sections.lds.h b/include/asm-generic/bounded_sections.lds.h
new file mode 100644
index 000000000000..8c29293ca7fb
--- /dev/null
+++ b/include/asm-generic/bounded_sections.lds.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _ASM_GENERIC_BOUNDED_SECTIONS_H
+#define _ASM_GENERIC_BOUNDED_SECTIONS_H
+
+#define BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_)	\
+	_BEGIN_##_label_ = .;						\
+	KEEP(*(_sec_))							\
+	_END_##_label_ = .;
+
+#define BOUNDED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_)	\
+	_label_##_BEGIN_ = .;						\
+	KEEP(*(_sec_))							\
+	_label_##_END_ = .;
+
+#define BOUNDED_SECTION_BY(_sec_, _label_)				\
+	BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, __start, __stop)
+
+#define BOUNDED_SECTION(_sec)	 BOUNDED_SECTION_BY(_sec, _sec)
+
+#define HEADERED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_, _HDR_) \
+	_HDR_##_label_	= .;						\
+	KEEP(*(.gnu.linkonce.##_sec_))					\
+	BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_)
+
+#define HEADERED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_, _HDR_) \
+	_label_##_HDR_ = .;						\
+	KEEP(*(.gnu.linkonce.##_sec_))					\
+	BOUNDED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_)
+
+#define HEADERED_SECTION_BY(_sec_, _label_)				\
+	HEADERED_SECTION_PRE_LABEL(_sec_, _label_, __start, __stop)
+
+#define HEADERED_SECTION(_sec)	 HEADERED_SECTION_BY(_sec, _sec)
+
+#endif /* _ASM_GENERIC_BOUNDED_SECTIONS_H */
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 5659f4b5a125..f5ddf31b7f26 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -50,6 +50,7 @@
  *               [__nosave_begin, __nosave_end] for the nosave data
  */
 
+#include <asm-generic/bounded_sections.lds.h>
 #include <asm-generic/codetag.lds.h>
 
 #ifndef LOAD_OFFSET
@@ -211,36 +212,6 @@
 # endif
 #endif
 
-#define BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_)	\
-	_BEGIN_##_label_ = .;						\
-	KEEP(*(_sec_))							\
-	_END_##_label_ = .;
-
-#define BOUNDED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_)	\
-	_label_##_BEGIN_ = .;						\
-	KEEP(*(_sec_))							\
-	_label_##_END_ = .;
-
-#define BOUNDED_SECTION_BY(_sec_, _label_)				\
-	BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, __start, __stop)
-
-#define BOUNDED_SECTION(_sec)	 BOUNDED_SECTION_BY(_sec, _sec)
-
-#define HEADERED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_, _HDR_) \
-	_HDR_##_label_	= .;						\
-	KEEP(*(.gnu.linkonce.##_sec_))					\
-	BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_)
-
-#define HEADERED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_, _HDR_) \
-	_label_##_HDR_ = .;						\
-	KEEP(*(.gnu.linkonce.##_sec_))					\
-	BOUNDED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_)
-
-#define HEADERED_SECTION_BY(_sec_, _label_)				\
-	HEADERED_SECTION_PRE_LABEL(_sec_, _label_, __start, __stop)
-
-#define HEADERED_SECTION(_sec)	 HEADERED_SECTION_BY(_sec, _sec)
-
 #ifdef CONFIG_TRACE_BRANCH_PROFILING
 #define LIKELY_PROFILE()						\
 	BOUNDED_SECTION_BY(_ftrace_annotated_branch, _annotated_branch_profile)

-- 
2.54.0

[PATCH v4 2/5] vmlinux.lds.h: drop unused HEADERED_SECTION* macros

[Jim Cromie]

These macros are unused, no point in carrying them any more.

NB: these macros were just moved to bounded_sections.lds.h, from
vmlinux.lds.h, which is the known entity, and therefore more
meaningful in the 1-line summary, so thats what I used as the topic.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 include/asm-generic/bounded_sections.lds.h | 15 ---------------
 1 file changed, 15 deletions(-)

diff --git a/include/asm-generic/bounded_sections.lds.h b/include/asm-generic/bounded_sections.lds.h
index 8c29293ca7fb..268cdc34389b 100644
--- a/include/asm-generic/bounded_sections.lds.h
+++ b/include/asm-generic/bounded_sections.lds.h
@@ -18,19 +18,4 @@
 
 #define BOUNDED_SECTION(_sec)	 BOUNDED_SECTION_BY(_sec, _sec)
 
-#define HEADERED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_, _HDR_) \
-	_HDR_##_label_	= .;						\
-	KEEP(*(.gnu.linkonce.##_sec_))					\
-	BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_)
-
-#define HEADERED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_, _HDR_) \
-	_label_##_HDR_ = .;						\
-	KEEP(*(.gnu.linkonce.##_sec_))					\
-	BOUNDED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_)
-
-#define HEADERED_SECTION_BY(_sec_, _label_)				\
-	HEADERED_SECTION_PRE_LABEL(_sec_, _label_, __start, __stop)
-
-#define HEADERED_SECTION(_sec)	 HEADERED_SECTION_BY(_sec, _sec)
-
 #endif /* _ASM_GENERIC_BOUNDED_SECTIONS_H */

-- 
2.54.0

[PATCH v4 3/5] vmlinux.lds.h: Fix ALIGN(8) omission causing NULL ptr on i386

[Jim Cromie]

Almost all uses of the BOUNDED_SECTION macros are ALIGN(8), either
explicitly, or by being below an aligned section containing x*8 byte
objects.  The noteworthy exception is BOUNDED_SECTION(__dyndbg), which
immediately follows BOUNDED_SECTION(__dyndbg_classes).

On i386, struct _ddebug_classmap is 28 bytes, so without an explicit
ALIGN(8) in the macro, the following __dyndbg section gets misaligned,
causing a NULL ptr deref in dynamic_debug_init().

So fix this with an explicit ALIGN(8) in the existing BOUNDED_SECTION
macros, and introduce _ALIGNED variants to handle the cases with an
explicit . = ALIGN(x)

Also add explicit alignments for: EXCEPTION_TABLE, ORC_UNWIND_TABLE,
TRACEDATA, INIT_SETUP, and NOTES.

update BOUNDED_SECTION uses inside . = ALIGN(x) stanzas to use
_ALIGNED variants, but keep the outer ALIGNs so the symbols between
them are not "re-aligned".

In particular, scripts/sorttable.c does not tolerate sloppy padding.

At the top of ORC_UNWIND_TABLE, add . = ALIGN(4) to match the struct
orc_header __align() call in the code:

commit b9f174c811e3 ("x86/unwind/orc: Add ELF section with ORC version identifier")

Suggested-by: Louis Chauvet <louis.chauvet@bootlin.com>  # _ALIGNED variants.
Link: https://lore.kernel.org/lkml/177402491426.6181.12855763650074831089.b4-review@b4/
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
v3:

sashiko complained about NOTES and .BTF_ids.
gemini asserts that NOTES are natively 4-byte aligned, add comment repeating it.
.BTF_ids doesnt use BOUNDED_BY, since start/end isnt needed;
sashiko evidently got confused by immediately preceding usage.

v2:

sashiko picked up 2 cases, added to the explicit list above
https://sashiko.dev/#/patchset/20260515-asm-generic-1-v3-0-680b273666d4%40gmail.com
---
 include/asm-generic/bounded_sections.lds.h | 17 ++++++++++++++---
 include/asm-generic/vmlinux.lds.h          | 18 ++++++++++--------
 2 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/include/asm-generic/bounded_sections.lds.h b/include/asm-generic/bounded_sections.lds.h
index 268cdc34389b..8ff3e3420f60 100644
--- a/include/asm-generic/bounded_sections.lds.h
+++ b/include/asm-generic/bounded_sections.lds.h
@@ -3,19 +3,30 @@
 #ifndef _ASM_GENERIC_BOUNDED_SECTIONS_H
 #define _ASM_GENERIC_BOUNDED_SECTIONS_H
 
-#define BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_)	\
+#define BOUNDED_SECTION_PRE_LABEL_ALIGNED(_sec_, _label_, _BEGIN_, _END_, _ALIGNED_) \
+	. = ALIGN(_ALIGNED_);						\
 	_BEGIN_##_label_ = .;						\
 	KEEP(*(_sec_))							\
 	_END_##_label_ = .;
 
-#define BOUNDED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_)	\
+#define BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, _BEGIN_, _END_)	\
+	BOUNDED_SECTION_PRE_LABEL_ALIGNED(_sec_, _label_, _BEGIN_, _END_, 8)
+
+#define BOUNDED_SECTION_POST_LABEL_ALIGNED(_sec_, _label_, _BEGIN_, _END_, _ALIGNED_) \
+	. = ALIGN(_ALIGNED_);						\
 	_label_##_BEGIN_ = .;						\
 	KEEP(*(_sec_))							\
 	_label_##_END_ = .;
 
+#define BOUNDED_SECTION_POST_LABEL(_sec_, _label_, _BEGIN_, _END_)	\
+	BOUNDED_SECTION_POST_LABEL_ALIGNED(_sec_, _label_, _BEGIN_, _END_, 8)
+
 #define BOUNDED_SECTION_BY(_sec_, _label_)				\
 	BOUNDED_SECTION_PRE_LABEL(_sec_, _label_, __start, __stop)
 
-#define BOUNDED_SECTION(_sec)	 BOUNDED_SECTION_BY(_sec, _sec)
+#define BOUNDED_SECTION_BY_ALIGNED(_sec_, _label_, _ALIGNED_)		\
+	BOUNDED_SECTION_PRE_LABEL_ALIGNED(_sec_, _label_, __start, __stop, _ALIGNED_)
+
+#define BOUNDED_SECTION(_sec)   BOUNDED_SECTION_BY(_sec, _sec)
 
 #endif /* _ASM_GENERIC_BOUNDED_SECTIONS_H */
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index f5ddf31b7f26..f29fc079e37e 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -640,7 +640,7 @@
 #define EXCEPTION_TABLE(align)						\
 	. = ALIGN(align);						\
 	__ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {		\
-		BOUNDED_SECTION_BY(__ex_table, ___ex_table)		\
+		BOUNDED_SECTION_BY_ALIGNED(__ex_table, ___ex_table, align) \
 	}
 
 /*
@@ -650,7 +650,7 @@
 #define BTF								\
 	. = ALIGN(PAGE_SIZE);						\
 	.BTF : AT(ADDR(.BTF) - LOAD_OFFSET) {				\
-		BOUNDED_SECTION_BY(.BTF, _BTF)				\
+		BOUNDED_SECTION_BY_ALIGNED(.BTF, _BTF, PAGE_SIZE)	\
 	}								\
 	. = ALIGN(PAGE_SIZE);						\
 	.BTF_ids : AT(ADDR(.BTF_ids) - LOAD_OFFSET) {			\
@@ -832,16 +832,17 @@
 
 #ifdef CONFIG_UNWINDER_ORC
 #define ORC_UNWIND_TABLE						\
+	. = ALIGN(4);							\
 	.orc_header : AT(ADDR(.orc_header) - LOAD_OFFSET) {		\
-		BOUNDED_SECTION_BY(.orc_header, _orc_header)		\
+		BOUNDED_SECTION_BY_ALIGNED(.orc_header, _orc_header, 4)	\
 	}								\
 	. = ALIGN(4);							\
 	.orc_unwind_ip : AT(ADDR(.orc_unwind_ip) - LOAD_OFFSET) {	\
-		BOUNDED_SECTION_BY(.orc_unwind_ip, _orc_unwind_ip)	\
+		BOUNDED_SECTION_BY_ALIGNED(.orc_unwind_ip, _orc_unwind_ip, 4)\
 	}								\
 	. = ALIGN(2);							\
 	.orc_unwind : AT(ADDR(.orc_unwind) - LOAD_OFFSET) {		\
-		BOUNDED_SECTION_BY(.orc_unwind, _orc_unwind)		\
+		BOUNDED_SECTION_BY_ALIGNED(.orc_unwind, _orc_unwind, 2)	\
 	}								\
 	text_size = _etext - _stext;					\
 	. = ALIGN(4);							\
@@ -869,7 +870,7 @@
 #define TRACEDATA							\
 	. = ALIGN(4);							\
 	.tracedata : AT(ADDR(.tracedata) - LOAD_OFFSET) {		\
-		BOUNDED_SECTION_POST_LABEL(.tracedata, __tracedata, _start, _end) \
+		BOUNDED_SECTION_POST_LABEL_ALIGNED(.tracedata, __tracedata, _start, _end, 4) \
 	}
 #else
 #define TRACEDATA
@@ -898,13 +899,14 @@
 		*(.note.gnu.property)					\
 	}								\
 	.notes : AT(ADDR(.notes) - LOAD_OFFSET) {			\
-		BOUNDED_SECTION_BY(.note.*, _notes)			\
+		/* *(.note.*) are natively 4-byte aligned */		\
+		BOUNDED_SECTION_BY_ALIGNED(.note.*, _notes, 4)		\
 	} NOTES_HEADERS							\
 	NOTES_HEADERS_RESTORE
 
 #define INIT_SETUP(initsetup_align)					\
 		. = ALIGN(initsetup_align);				\
-		BOUNDED_SECTION_POST_LABEL(.init.setup, __setup, _start, _end)
+		BOUNDED_SECTION_POST_LABEL_ALIGNED(.init.setup, __setup, _start, _end, initsetup_align)
 
 #define INIT_CALLS_LEVEL(level)						\
 		__initcall##level##_start = .;				\

-- 
2.54.0

[PATCH v4 4/5] vmlinux.lds.h: remove redundant ALIGN(8) directives

[Jim Cromie]

The BOUNDED_SECTION_PRE_LABEL and BOUNDED_SECTION_POST_LABEL macros
were recently updated to inherently enforce an 8-byte alignment. This
makes the explicit '. = ALIGN(8);' statements preceding 'naked' macro
calls in vmlinux.lds.h redundant.

Remove these redundant alignment directives to clean up the file and
clarify that the macros handle their own alignment padding.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
 include/asm-generic/vmlinux.lds.h | 13 -------------
 1 file changed, 13 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index f29fc079e37e..3758a79d0430 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -228,7 +228,6 @@
 
 #ifdef CONFIG_KPROBES
 #define KPROBE_BLACKLIST()				\
-	. = ALIGN(8);					\
 	BOUNDED_SECTION(_kprobe_blacklist)
 #else
 #define KPROBE_BLACKLIST()
@@ -244,7 +243,6 @@
 
 #ifdef CONFIG_EVENT_TRACING
 #define FTRACE_EVENTS()							\
-	. = ALIGN(8);							\
 	BOUNDED_SECTION(_ftrace_events)					\
 	BOUNDED_SECTION_BY(_ftrace_eval_map, _ftrace_eval_maps)
 #else
@@ -261,7 +259,6 @@
 
 #ifdef CONFIG_FTRACE_SYSCALLS
 #define TRACE_SYSCALLS()			\
-	. = ALIGN(8);				\
 	BOUNDED_SECTION_BY(__syscalls_metadata, _syscalls_metadata)
 #else
 #define TRACE_SYSCALLS()
@@ -276,7 +273,6 @@
 
 #ifdef CONFIG_SERIAL_EARLYCON
 #define EARLYCON_TABLE()						\
-	. = ALIGN(8);							\
 	BOUNDED_SECTION_POST_LABEL(__earlycon_table, __earlycon_table, , _end)
 #else
 #define EARLYCON_TABLE()
@@ -284,11 +280,9 @@
 
 #ifdef CONFIG_SECURITY
 #define LSM_TABLE()					\
-	. = ALIGN(8);					\
 	BOUNDED_SECTION_PRE_LABEL(.lsm_info.init, _lsm_info, __start, __end)
 
 #define EARLY_LSM_TABLE()						\
-	. = ALIGN(8);							\
 	BOUNDED_SECTION_PRE_LABEL(.early_lsm_info.init, _early_lsm_info, __start, __end)
 #else
 #define LSM_TABLE()
@@ -314,7 +308,6 @@
 
 #ifdef CONFIG_ACPI
 #define ACPI_PROBE_TABLE(name)						\
-	. = ALIGN(8);							\
 	BOUNDED_SECTION_POST_LABEL(__##name##_acpi_probe_table,		\
 				   __##name##_acpi_probe_table,, _end)
 #else
@@ -323,7 +316,6 @@
 
 #ifdef CONFIG_THERMAL
 #define THERMAL_TABLE(name)						\
-	. = ALIGN(8);							\
 	BOUNDED_SECTION_POST_LABEL(__##name##_thermal_table,		\
 				   __##name##_thermal_table,, _end)
 #else
@@ -403,12 +395,10 @@
 	__end_init_stack = .;
 
 #define JUMP_TABLE_DATA							\
-	. = ALIGN(8);							\
 	BOUNDED_SECTION_BY(__jump_table, ___jump_table)
 
 #ifdef CONFIG_HAVE_STATIC_CALL_INLINE
 #define STATIC_CALL_DATA						\
-	. = ALIGN(8);							\
 	BOUNDED_SECTION_BY(.static_call_sites, _static_call_sites)	\
 	BOUNDED_SECTION_BY(.static_call_tramp_key, _static_call_tramp_key)
 #else
@@ -453,7 +443,6 @@
 		*(.rodata) *(.rodata.*) *(.data.rel.ro*)		\
 		SCHED_DATA						\
 		RO_AFTER_INIT_DATA	/* Read only after init */	\
-		. = ALIGN(8);						\
 		BOUNDED_SECTION_BY(__tracepoints_ptrs, ___tracepoints_ptrs) \
 		*(__tracepoints_strings)/* Tracepoints: strings */	\
 	}								\
@@ -947,12 +936,10 @@
 
 /* Alignment must be consistent with (kunit_suite *) in include/kunit/test.h */
 #define KUNIT_TABLE()							\
-		. = ALIGN(8);						\
 		BOUNDED_SECTION_POST_LABEL(.kunit_test_suites, __kunit_suites, _start, _end)
 
 /* Alignment must be consistent with (kunit_suite *) in include/kunit/test.h */
 #define KUNIT_INIT_TABLE()						\
-		. = ALIGN(8);						\
 		BOUNDED_SECTION_POST_LABEL(.kunit_init_test_suites, \
 				__kunit_init_suites, _start, _end)
 

-- 
2.54.0

[PATCH v4 5/5] dyndbg.lds.S: fix lost dyndbg sections in modules

[Jim Cromie]

With CONFIG_DRM_USE_DYNAMIC_DEBUG=y, several build configs had
problems with __dyndbg* sections getting lost in drm drivers.  Fix
this by following the model demonstrated in codetag.lds.h.

Introduce include/asm-generic/dyndbg.lds.h, to bundle dynamic-debug's
multiple sections together, into 2 macros:

vmlinux.lds.h DATA_DATA: move the 2 BOUNDED_SECTION_BY(__dyndbg*)
calls into dyndbg.lds.h DYNDBG_SECTIONS(). vmlinux.lds.h now includes
the new file and calls the new macro.

MOD_DYNDBG_SECTIONS keeps the 2 sections by name, aligns them and sets
the output address to 0 when the sections are empty.

dyndbg.lds.h includes (reuses) bounded-section.lds.h

scripts/module.lds.S: now calls MOD_DYNDBG_SECTIONS right before the
CODETAG macro (consistent with their placements in vmlinux.lds.h), and
also includes dyndbg.lds.h

This isolates vmlinux.lds.h from further __dyndbg section additions.

CC: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
---
v3: move #includes to top, drop extra ALIGN(8) in DYNDBG_SECTIONS, add RvBy

v2: Address linker script review feedback for relocatable modules.

MOD_DYNDBG_SECTIONS() used the BOUNDED_SECTION_BY() macro, which
proved problematic for kernel modules for two reasons:

1. Unwanted Empty Sections:
   BOUNDED_SECTION_BY() automatically generates `__start` and `__stop`
   symbols. When applied to `MOD_DYNDBG_SECTIONS()`, the linker assumes
   the sections are populated due to the symbol definitions, forcing an
   empty `__dyndbg` and `__dyndbg_classes` output section in every
   compiled module, even those without dynamic debug configuration.
   Since the module loader uses `section_objs()` to locate data via
   ELF headers instead of relying on `__start`/`__stop` symbols, these
   assignments are completely unnecessary.

2. Non-zero Output Addresses:
   During relocatable linking (e.g., `ld.bfd -r`), omitting an explicit
   base address causes the section to inherit the current location
   counter. This results in non-zero sh_addr values in `.ko` files,
   which is confusing, degrades compressibility, and can cause issues
   with external tools parsing the ELF.

Fix both issues by dropping `BOUNDED_SECTION_BY()` in favor of a simple
`KEEP(*(...))` constraint and explicitly defining the sections with a `0`
base address: `__dyndbg 0 : ALIGN(8) { ... }`.

fixup-inc-vml
---
 MAINTAINERS                       |  1 +
 include/asm-generic/dyndbg.lds.h  | 18 ++++++++++++++++++
 include/asm-generic/vmlinux.lds.h |  6 ++----
 scripts/module.lds.S              |  2 ++
 4 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index 15011f5752a9..cfc2695d9bbe 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9178,6 +9178,7 @@ DYNAMIC DEBUG
 M:	Jason Baron <jbaron@akamai.com>
 M:	Jim Cromie <jim.cromie@gmail.com>
 S:	Maintained
+F:	include/asm-generic/dyndbg.lds.h
 F:	include/linux/dynamic_debug.h
 F:	lib/dynamic_debug.c
 F:	lib/test_dynamic_debug.c
diff --git a/include/asm-generic/dyndbg.lds.h b/include/asm-generic/dyndbg.lds.h
new file mode 100644
index 000000000000..9d8951bef688
--- /dev/null
+++ b/include/asm-generic/dyndbg.lds.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __ASM_GENERIC_DYNDBG_LDS_H
+#define __ASM_GENERIC_DYNDBG_LDS_H
+
+#include <asm-generic/bounded_sections.lds.h>
+#define DYNDBG_SECTIONS()					\
+	BOUNDED_SECTION_BY(__dyndbg, ___dyndbg)			\
+	BOUNDED_SECTION_BY(__dyndbg_classes, ___dyndbg_classes)
+
+#define MOD_DYNDBG_SECTIONS()						\
+	__dyndbg 0 : ALIGN(8) {						\
+		KEEP(*(__dyndbg))					\
+	}								\
+	__dyndbg_classes 0 : ALIGN(8) {					\
+		KEEP(*(__dyndbg_classes))				\
+	}
+
+#endif /* __ASM_GENERIC_DYNDBG_LDS_H */
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 3758a79d0430..bd60f278f762 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -52,6 +52,7 @@
 
 #include <asm-generic/bounded_sections.lds.h>
 #include <asm-generic/codetag.lds.h>
+#include <asm-generic/dyndbg.lds.h>
 
 #ifndef LOAD_OFFSET
 #define LOAD_OFFSET 0
@@ -344,10 +345,7 @@
 	*(.data..do_once)						\
 	STRUCT_ALIGN();							\
 	*(__tracepoints)						\
-	/* implement dynamic printk debug */				\
-	. = ALIGN(8);							\
-	BOUNDED_SECTION_BY(__dyndbg_classes, ___dyndbg_classes)		\
-	BOUNDED_SECTION_BY(__dyndbg, ___dyndbg)				\
+	DYNDBG_SECTIONS()						\
 	CODETAG_SECTIONS()						\
 	LIKELY_PROFILE()		       				\
 	BRANCH_PROFILE()						\
diff --git a/scripts/module.lds.S b/scripts/module.lds.S
index b62683061d79..2e62dc5bd5d4 100644
--- a/scripts/module.lds.S
+++ b/scripts/module.lds.S
@@ -10,6 +10,7 @@
 #endif
 
 #include <asm-generic/codetag.lds.h>
+#include <asm-generic/dyndbg.lds.h>
 
 SECTIONS {
 	/DISCARD/ : {
@@ -61,6 +62,7 @@ SECTIONS {
 		*(.rodata..L*)
 	}
 
+	MOD_DYNDBG_SECTIONS()
 	MOD_SEPARATE_CODETAG_SECTIONS()
 }
 

-- 
2.54.0