Re: [PATCH v3 01/20] kbuild: do not allocate .modinfo in vmlinux

[Nathan Chancellor <nathan@kernel.org>]

On Thu, Sep 17, 2026 at 09:52:32AM -0700, Kees Cook wrote:
> On Thu, Sep 17, 2026 at 05:06:11PM +0100, Lorenzo Stoakes (ARM) wrote:
> > -# .modinfo in vmlinux.unstripped is aligned to 8 bytes for compatibility with
> > -# tools that expect vmlinux to have sufficiently aligned sections but the
> > -# additional bytes used for padding .modinfo to satisfy this requirement break
> > -# certain versions of kmod with
> > -#
> > -#   depmod: ERROR: kmod_builtin_iter_next: unexpected string without modname prefix
> > -#
> > -# Strip the trailing padding bytes after extracting .modinfo to comply with
> > -# what kmod expects to parse.
> 
> This comment still seems useful here (afaict the stripping is still
> happening with the "sed"). Maybe better to leave it, or future readers
> are left wondering what the sed is for?

Thanks for bringing this up. I think we can actually get rid of that sed
and comment altogether. It was added by

  a26a6c93edfe ("kbuild: Strip trailing padding bytes from modules.builtin.modinfo")

to fix

  d50f21091358 ("kbuild: align modinfo section for Secureboot Authenticode EDK2 compat")

but I do not think that this alignment is needed anymore since I
properly fixed Dimitri's issue in

  8678591b4746 ("kbuild: Split .modinfo out from ELF_DETAILS")

So I think we could go with something like

From 008046b33ef4b476048e3ddb2c679a453254e535 Mon Sep 17 00:00:00 2001
From: Nathan Chancellor <nathan@kernel.org>
Date: Thu, 17 Sep 2026 17:29:53 -0700
Subject: [PATCH] kbuild: Remove alignment on .modinfo section

Commit d50f21091358 ("kbuild: align modinfo section for Secureboot
Authenticode EDK2 compat") aligned .modinfo because it appeared in the
x86_64 compressed kernel image after commit 3e86e4d74c04 ("kbuild: keep
.modinfo section in vmlinux.unstripped"), breaking boot.

Commit 8678591b4746 ("kbuild: Split .modinfo out from ELF_DETAILS")
properly addresses .modinfo appearing in unexpected contexts like
compressed images by moving it out of ELF_DETAILS and explicitly
specifying its location in every architecture's vmlinux linker script or
discarding it where it may appear elsewhere.

Effectively revert commit d50f21091358 ("kbuild: align modinfo section
for Secureboot Authenticode EDK2 compat") and its follow up fix,
commit a26a6c93edfe ("kbuild: Strip trailing padding bytes from
modules.builtin.modinfo"), as they are no longer necessary in the
current tree. This simplifies future cleanups.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 include/asm-generic/vmlinux.lds.h |  2 +-
 scripts/Makefile.vmlinux          | 10 ----------
 2 files changed, 1 insertion(+), 11 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index b2988aa12f66..26201821ea7f 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -855,7 +855,7 @@
 		KLP_SYMID
 
 #define MODINFO								\
-		.modinfo : { *(.modinfo) . = ALIGN(8); }
+		.modinfo : { *(.modinfo) }
 
 #ifdef CONFIG_GENERIC_BUG
 #define BUG_TABLE							\
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index fcae1e432d9a..6833b517cacb 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -102,18 +102,8 @@ vmlinux: vmlinux.unstripped FORCE
 # modules.builtin.modinfo
 # ---------------------------------------------------------------------------
 
-# .modinfo in vmlinux.unstripped is aligned to 8 bytes for compatibility with
-# tools that expect vmlinux to have sufficiently aligned sections but the
-# additional bytes used for padding .modinfo to satisfy this requirement break
-# certain versions of kmod with
-#
-#   depmod: ERROR: kmod_builtin_iter_next: unexpected string without modname prefix
-#
-# Strip the trailing padding bytes after extracting .modinfo to comply with
-# what kmod expects to parse.
 quiet_cmd_modules_builtin_modinfo = GEN     $@
       cmd_modules_builtin_modinfo = $(cmd_objcopy); \
-                                    sed -i 's/\x00\+$$/\x00/g' $@; \
                                     chmod -x $@
 
 OBJCOPYFLAGS_modules.builtin.modinfo := -j .modinfo -O binary
-- 

Then this patch becomes much more obvious (at least to me)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 26201821ea7f..a6730d34e8c6 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -855,7 +855,7 @@
 		KLP_SYMID
 
 #define MODINFO								\
-		.modinfo : { *(.modinfo) }
+		.modinfo (INFO) : { *(.modinfo) }
 
 #ifdef CONFIG_GENERIC_BUG
 #define BUG_TABLE							\
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index 6833b517cacb..95b523fe4f9e 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -89,11 +89,8 @@ remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel.*'
 
 remove-symbols := -w --strip-unneeded-symbol='__mod_device_table__*'
 
-# To avoid warnings: "empty loadable segment detected at ..." from GNU objcopy,
-# it is necessary to remove the PT_LOAD flag from the segment.
 quiet_cmd_strip_relocs = OBJCOPY $@
-      cmd_strip_relocs = $(OBJCOPY) $(patsubst %,--set-section-flags %=noload,$(remove-section-y)) $< $@; \
-                         $(OBJCOPY) $(addprefix --remove-section=,$(remove-section-y)) $(remove-symbols) $@
+      cmd_strip_relocs = $(OBJCOPY) $(addprefix --remove-section=,$(remove-section-y)) $(remove-symbols) $< $@
 
 targets += vmlinux
 vmlinux: vmlinux.unstripped FORCE
@@ -103,10 +100,7 @@ vmlinux: vmlinux.unstripped FORCE
 # ---------------------------------------------------------------------------
 
 quiet_cmd_modules_builtin_modinfo = GEN     $@
-      cmd_modules_builtin_modinfo = $(cmd_objcopy); \
-                                    chmod -x $@
-
-OBJCOPYFLAGS_modules.builtin.modinfo := -j .modinfo -O binary
+      cmd_modules_builtin_modinfo = $(OBJCOPY) -O binary -j .modinfo --dump-section .modinfo=$@ $< /dev/null
 
 targets += modules.builtin.modinfo
 modules.builtin.modinfo: vmlinux.unstripped FORCE
--

Thoughts?

-- 
Cheers,
Nathan