Commit 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
changed the ELF type of .btf.vmlinux.bin.o to ET_REL via dd, which works
fine for little endian platforms:
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
-00000010 03 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
+00000010 01 00 b7 00 01 00 00 00 00 00 00 80 00 80 ff ff |................|
However, for big endian platforms, it changes the wrong byte, resulting
in an invalid ELF file type, which ld.lld rejects:
00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
-00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
+00000010 01 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
Type: <unknown>: 103
ld.lld: error: .btf.vmlinux.bin.o: unknown file type
Fix this by updating the entire 16-bit e_type field rather than just a
single byte, so that everything works correctly for all platforms and
linkers.
00000000 7f 45 4c 46 02 02 01 00 00 00 00 00 00 00 00 00 |.ELF............|
-00000010 00 03 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
+00000010 00 01 00 16 00 00 00 01 00 00 00 00 00 10 00 00 |................|
Type: REL (Relocatable file)
While in the area, update the comment to mention that binutils 2.35+
matches LLD's behavior of rejecting an ET_EXEC input, which occurred
after the comment was added.
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
Link: https://github.com/llvm/llvm-project/pull/75643
Suggested-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
---
Changes in v2:
- Rather than change the seek value for dd, update the entire e_type
field (Masahiro). Due to this change, I did not carry forward the
tags of v1.
- Slightly update commit message to remove mention of ET_EXEC, which
does not match the dump (Masahiro).
- Update comment to mention binutils 2.35+ has the same behavior as LLD
(Fangrui).
- Link to v1: https://lore.kernel.org/r/20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-v1-1-cb3112491edc@xxxxxxxxxx
---
scripts/link-vmlinux.sh | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index a432b171be82..7862a8101747 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -135,8 +135,13 @@ gen_btf()
${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \
--strip-all ${1} ${2} 2>/dev/null
# Change e_type to ET_REL so that it can be used to link final vmlinux.
- # Unlike GNU ld, lld does not allow an ET_EXEC input.
- printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 status=none
+ # GNU ld 2.35+ and lld do not allow an ET_EXEC input.
+ if is_enabled CONFIG_CPU_BIG_ENDIAN; then
+ et_rel='\0\1'
+ else
+ et_rel='\1\0'
+ fi
+ printf "${et_rel}" | dd of=${2} conv=notrunc bs=1 seek=16 status=none
}
# Create ${2} .S file with all symbols from the ${1} object file
---
base-commit: 54be6c6c5ae8e0d93a6c4641cb7528eb0b6ba478
change-id: 20240208-fix-elf-type-btf-vmlinux-bin-o-big-endian-dbc55a1e1296
Best regards,
--
Nathan Chancellor <nathan@xxxxxxxxxx>
