Re: [PATCH v7 3/8] kbuild: keep .modinfo section in vmlinux.unstripped

[Alexey Gladkov <legion@kernel.org>]

On Tue, Sep 16, 2025 at 11:36:54AM +0200, Nicolas Schier wrote:
> On Tue, Sep 16, 2025 at 09:12:22AM +0200, Alexey Gladkov wrote:
> > On Mon, Sep 15, 2025 at 07:56:16AM +0200, Nicolas Schier wrote:
> > > On Mon, Aug 18, 2025 at 06:54:57PM +0200, Alexey Gladkov wrote:
> > > > From: Masahiro Yamada <masahiroy@kernel.org>
> > > > 
> > > > Keep the .modinfo section during linking, but strip it from the final
> > > > vmlinux.
> > > > 
> > > > Adjust scripts/mksysmap to exclude modinfo symbols from kallsyms.
> > > > 
> > > > This change will allow the next commit to extract the .modinfo section
> > > > from the vmlinux.unstripped intermediate.
> > > > 
> > > > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > > > ---
> > > >  include/asm-generic/vmlinux.lds.h | 2 +-
> > > >  scripts/Makefile.vmlinux          | 2 +-
> > > >  scripts/mksysmap                  | 3 +++
> > > >  3 files changed, 5 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> > > > index ae2d2359b79e9..cfa63860dfd4c 100644
> > > > --- a/include/asm-generic/vmlinux.lds.h
> > > > +++ b/include/asm-generic/vmlinux.lds.h
> > > > @@ -831,6 +831,7 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
> > > >  
> > > >  /* Required sections not related to debugging. */
> > > >  #define ELF_DETAILS							\
> > > > +		.modinfo : { *(.modinfo) }				\
> > > >  		.comment 0 : { *(.comment) }				\
> > > >  		.symtab 0 : { *(.symtab) }				\
> > > >  		.strtab 0 : { *(.strtab) }				\
> > > > @@ -1044,7 +1045,6 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
> > > >  	*(.discard.*)							\
> > > >  	*(.export_symbol)						\
> > > >  	*(.no_trim_symbol)						\
> > > > -	*(.modinfo)							\
> > > >  	/* ld.bfd warns about .gnu.version* even when not emitted */	\
> > > >  	*(.gnu.version*)						\
> > > >  
> > > > diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
> > > > index 4f2d4c3fb7372..e2ceeb9e168d4 100644
> > > > --- a/scripts/Makefile.vmlinux
> > > > +++ b/scripts/Makefile.vmlinux
> > > > @@ -86,7 +86,7 @@ endif
> > > >  # vmlinux
> > > >  # ---------------------------------------------------------------------------
> > > >  
> > > > -remove-section-y                                   :=
> > > > +remove-section-y                                   := .modinfo
> > > >  remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel*'
> > > >  
> > > >  quiet_cmd_strip_relocs = OBJCOPY $@
> > > > diff --git a/scripts/mksysmap b/scripts/mksysmap
> > > > index 3accbdb269ac7..a607a0059d119 100755
> > > > --- a/scripts/mksysmap
> > > > +++ b/scripts/mksysmap
> > > > @@ -79,6 +79,9 @@
> > > >  / _SDA_BASE_$/d
> > > >  / _SDA2_BASE_$/d
> > > >  
> > > > +# MODULE_INFO()
> > > > +/ __UNIQUE_ID_modinfo[0-9]*$/d
> > > > +
> > > >  # ---------------------------------------------------------------------------
> > > >  # Ignored patterns
> > > >  #  (symbols that contain the pattern are ignored)
> > > > -- 
> > > > 2.50.1
> > > > 
> > > 
> > > Hi Alexey,
> > > 
> > > with this patch applied, I still get a warning from objcpy as Masahiro
> > > and Stephen wrote [1,2]
> > > 
> > >   SORTTAB vmlinux.unstripped
> > > + sorttable vmlinux.unstripped
> > > + nm -S vmlinux.unstripped
> > > + ./scripts/sorttable -s .tmp_vmlinux.nm-sort vmlinux.unstripped
> > > + is_enabled CONFIG_KALLSYMS
> > > + grep -q ^CONFIG_KALLSYMS=y include/config/auto.conf
> > > + cmp -s System.map .tmp_vmlinux2.syms
> > > + echo vmlinux.unstripped: ../scripts/link-vmlinux.sh
> > > # OBJCOPY vmlinux
> > >   objcopy --remove-section=.modinfo vmlinux.unstripped vmlinux
> > > objcopy: vmlinux.unstripped: warning: empty loadable segment detected at vaddr=0xffff8000807a0000, is this intentional?
> > > 
> > > (arm64, allnoconfig)
> > > 
> > > Kind regards,
> > > Nicolas
> > > 
> > > 
> > > [1]: https://lore.kernel.org/linux-kbuild/CAK7LNAR-gD2H6Kk-rZjo0R3weTHCGTm0a=u2tRH1WWW6Sx6=RQ@mail.gmail.com/
> > > [2]: https://lore.kernel.org/lkml/20250730164047.7c4a731a@canb.auug.org.au/
> > > 
> > 
> > Hm. I missed that. I need to investigate how to fix this. Nothing comes
> > to mind right now.
> 
> Same here.  Only thing I could find until now is
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/diff/scripts/link-vmlinux.sh?id=90ceddcb495008ac8ba7a3dce297841efcd7d584
> 
> where '2>/dev/null' is appended exactly to prevent this very warning.
> But for me, it doesn't feel good doing that when stripping to vmlinux.

Yes, that's not a very good approach. It will hide other errors that will
definitely need to be seen. I think the commit you mentioned is actually
incorrect. I think there should be a different solution.

I think in the case of .modinfo, we can change the flag in the section
since we are going to delete it anyway.

diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index dbbe3bf0cf23..9a118b31d0dc 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -87,7 +87,8 @@ remove-section-$(CONFIG_ARCH_VMLINUX_NEEDS_RELOCS) += '.rel*'
 remove-symbols := -w --strip-symbol='__mod_device_table__*'
 
 quiet_cmd_strip_relocs = OBJCOPY $@
-      cmd_strip_relocs = $(OBJCOPY) $(addprefix --remove-section=,$(remove-section-y)) \
+      cmd_strip_relocs = $(OBJCOPY) $(patsubst %,--set-section-flags %=noload,$(remove-section-y)) $< && \
+                         $(OBJCOPY) $(addprefix --remove-section=,$(remove-section-y)) \
                          $(remove-symbols) $< $@
 
 targets += vmlinux
-- 
Rgrds, legion