[PATCH 5.15 5.10 5.4 0/1] arm64: fix Build ID if CONFIG_MODVERSIONS

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

Hi Greg,
    Our internal rpm build for aarch64 started failing after merging
v5.15.60.  The build actually succeeds, but packaging failed due to tools
which extract the Build ID from vmlinux.


Expected:
readelf -n vmlinux

Displaying notes found in: .notes
  Owner                Data size  Description
  GNU                  0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
    Build ID: ae5803ded69a15fb0a75905ec226a76cc1823d22
  Linux                0x00000004 func
   description data: 00 00 00 00
  Linux                0x00000001 OPEN
   description data: 00

Actual (post v5.15.60 merge):
readelf -n vmlinux
<no output>


Digging deeper...

Expected:
readelf --headers vmlinux | sed -ne '/Program Header/,$p'
Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000010000 0xffff800008000000 0xffff800008000000
                 0x0000000002012a00 0x000000000208f724  RWE    0x10000
  NOTE           0x0000000001705948 0xffff8000096f5948 0xffff8000096f5948
                 0x0000000000000054 0x0000000000000054  R      0x4
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RW     0x10

 Section to Segment mapping:
  Segment Sections...
   00     .head.text .text .got.plt .rodata .pci_fixup __ksymtab __ksymtab_gpl __kcrctab __kcrctab_gpl __ksymtab_strings __param __modver __ex_table .notes .hyp.rodata .init.text .exit.text .altinstructions .init.data .data..percpu .hyp.data..percpu .hyp.reloc .rela.dyn .data __bug_table .mmuoff.data.write .mmuoff.data.read .pecoff_edata_padding .bss
   01     .notes
   02

Actual:
readelf --headers vmlinux | sed -ne '/Program Header/,$p'
Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000010000 0xffff800008000000 0xffff800008000000
                 0x0000000002012a00 0x000000000208f724  RWE    0x10000
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RW     0x10

 Section to Segment mapping:
  Segment Sections...
   00     .head.text .text .got.plt .rodata .pci_fixup __ksymtab __ksymtab_gpl __kcrctab __kcrctab_gpl __ksymtab_strings __param __modver __ex_table .notes .hyp.rodata .init.text .exit.text .altinstructions .init.data .data..percpu .hyp.data..percpu .hyp.reloc .rela.dyn .data __bug_table .mmuoff.data.write .mmuoff.data.read .pecoff_edata_padding .bss
   01

readelf -n fails since NOTE segment is missing from vmlinux.

Why?

5.15 Commit: 4c7ee827da2c ("Makefile: link with -z noexecstack --no-warn-rwx-segments")
surfaced this issue.

1. Reverting this patch fixed this issue.

2. Removing all .note.GNU-stack sections in cmd_modversions_S also worked:

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 17aa8ef2d52a..b95cfbb43cee 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);				\

3. But the simplest fix I found was to remove -z noexecstack just for
head.S (this patch).


This issue exists, in my testing of arm64 builds, for stable versions
5.15.30+, 5.10.136+, and 5.4.210+
and reproduces with every attempted combination of gcc{11,12}
ld{2.36,2.37,2.38,2.39}.

It can also be reproduced upstream by cherry-picking 0d362be5b142 on-top until
7b4537199a4a ("kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS")
which was part of merge
df202b452fe6 ("Merge tag 'kbuild-v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild")

It seems kernels prior to v5.4 and 5.19+ use differing KBUILD rules
(with CONFIG_MODVERSIONS=y) for linking components of vmlinux, and in my
testing these other versions did not encounter this issue.

Other architectures besides arm64 might also have similar bug/feature of ld.
Though, x86_64 v5.15.60 worked as expected, so no further experiments
were performed for x86_64.

arm64 repro test:

make ARCH=arm64 mrproper
cp arch/arm64/configs/defconfig ".config"
scripts/config -e MODVERSIONS
make ARCH=arm64 olddefconfig
make ARCH=arm64 -j16 vmlinux
readelf -n vmlinux | grep -F "Build ID:"

Please consider applying for 5.15, 5.10, and 5.4.


Regards,

--Tom

Tom Saeger (1):
  arm64: fix Build ID if CONFIG_MODVERSIONS

 arch/arm64/kernel/Makefile | 5 +++++
 1 file changed, 5 insertions(+)


base-commit: e4a7232c917cd1b56d5b4fa9d7a23e3eabfecba0
-- 
2.38.1