[PATCH 5.15 5.10 5.4 v2] kbuild: fix Build ID if CONFIG_MODVERSIONS

[Tom Saeger <tom.saeger@oracle.com>]

Backport of:
commit 0d362be5b142 ("Makefile: link with -z noexecstack --no-warn-rwx-segments")
breaks arm64 Build ID when CONFIG_MODVERSIONS=y for all kernels
from: commit e4484a495586 ("Merge tag 'kbuild-fixes-v5.0' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild")
until: commit df202b452fe6 ("Merge tag 'kbuild-v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild")

Linus's tree doesn't have this issue since 0d362be5b142 was merged
after df202b452fe6 which included:
commit 7b4537199a4a ("kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS")

This kernel's KBUILD CONFIG_MODVERSIONS tooling compiles and links .S targets
with relocatable (-r) and now (-z noexecstack)
which results in ld adding a .note.GNU-stack section to .o files.
Final linking of vmlinux should add a .NOTES segment containing the
Build ID, but does NOT (on some architectures like arm64) if a
.note.GNU-stack section is found in .o's supplied during link
of vmlinux.

DISCARD .note.GNU-stack sections of .S targets.  Final link of
vmlinux then properly adds .NOTES segment containing Build ID that can
be read using tools like 'readelf -n'.

Fixes: 0d362be5b142 ("Makefile: link with -z noexecstack --no-warn-rwx-segments")
Cc: <stable@vger.kernel.org> # 5.15, 5.10, 5.4
Cc: <linux-kbuild@vger.kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Tom Saeger <tom.saeger@oracle.com>
---

v2:
  - Changed approach to append DISCARD section to generated linker script.
    - ld no longer emits warning (which was intent of 0d362b35b142) this
      addresses Nick's v1 feedback.
    - this is applied to all arches, not just arm64
  - added commit refs and notes why this doesn't occur in Linus's tree
    to address Greg's v1 feedback.
  - added Fixes: 0d362b35b142 requested by Nick
  - added note to changelog for 7b4537199a4a requested by Nick
  - build tested on arm64 and x86
   
   version           works(vmlinux contains Build ID)
   v4.14.302         x86, arm64
   v4.14.302.patched x86, arm64
   v4.19.269         x86, arm64
   v4.19.269.patched x86, arm64
   v5.4.227          x86
   v5.4.227.patched  x86, arm64
   v5.10.159         x86
   v5.10.159.patched x86, arm64
   v5.15.83          x86
   v5.15.83.patched  x86, arm64

v1: https://lore.kernel.org/all/cover.1670358255.git.tom.saeger@oracle.com/


 scripts/Makefile.build | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 17aa8ef2d52a..e3939676eeb5 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -379,6 +379,8 @@ cmd_modversions_S =								\
 	if $(OBJDUMP) -h $@ | grep -q __ksymtab; then				\
 		$(call cmd_gensymtypes_S,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\
 		    > $(@D)/.tmp_$(@F:.o=.ver);					\
+		echo "SECTIONS { /DISCARD/ : { *(.note.GNU-stack) } }"		\
+		>> $(@D)/.tmp_$(@F:.o=.ver); 					\
 										\
 		$(LD) $(KBUILD_LDFLAGS) -r -o $(@D)/.tmp_$(@F) $@ 		\
 			-T $(@D)/.tmp_$(@F:.o=.ver);				\

base-commit: fd6d66840b4269da4e90e1ea807ae3197433bc66
-- 
2.38.1