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| author | Stanislav Fomichev <sdf@google.com> | 2019-11-27 14:57:59 -0800 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2019-11-29 10:18:57 +0100 |
| commit | df786c9b947639aedbc7bb44b5dae2a7824af360 (patch) | |
| tree | c47ad5f82c960333514486f3b0b3572ffae569f5 /scripts | |
| parent | ce27709b8162e5c501bc54292b8bf6bdecc4bbd4 (diff) | |
| download | lwn-df786c9b947639aedbc7bb44b5dae2a7824af360.tar.gz lwn-df786c9b947639aedbc7bb44b5dae2a7824af360.zip | |
bpf: Force .BTF section start to zero when dumping from vmlinux
While trying to figure out why fentry_fexit selftest doesn't pass for me
(old pahole, broken BTF), I found out that my latest patch can break vmlinux
.BTF generation. objcopy preserves section start when doing --only-section,
so there is a chance (depending on where pahole inserts .BTF section) to
have leading empty zeroes. Let's explicitly force section offset to zero.
Before:
$ objcopy --set-section-flags .BTF=alloc -O binary \
--only-section=.BTF vmlinux .btf.vmlinux.bin
$ xxd .btf.vmlinux.bin | head -n1
00000000: 0000 0000 0000 0000 0000 0000 0000 0000 ................
After:
$ objcopy --change-section-address .BTF=0 \
--set-section-flags .BTF=alloc -O binary \
--only-section=.BTF vmlinux .btf.vmlinux.bin
$ xxd .btf.vmlinux.bin | head -n1
00000000: 9feb 0100 1800 0000 0000 0000 80e1 1c00 ................
^BTF magic
As part of this change, I'm also dropping '2>/dev/null' from objcopy
invocation to be able to catch possible other issues (objcopy doesn't
produce any warnings for me anymore, it did before with --dump-section).
Fixes: da5fb18225b4 ("bpf: Support pre-2.25-binutils objcopy for vmlinux BTF")
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Cc: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20191127225759.39923-1-sdf@google.com
Diffstat (limited to 'scripts')
| -rwxr-xr-x | scripts/link-vmlinux.sh | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh index 2998ddb323e3..436379940356 100755 --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -127,8 +127,9 @@ gen_btf() cut -d, -f1 | cut -d' ' -f2) bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \ awk '{print $4}') - ${OBJCOPY} --set-section-flags .BTF=alloc -O binary \ - --only-section=.BTF ${1} .btf.vmlinux.bin 2>/dev/null + ${OBJCOPY} --change-section-address .BTF=0 \ + --set-section-flags .BTF=alloc -O binary \ + --only-section=.BTF ${1} .btf.vmlinux.bin ${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \ --rename-section .data=.BTF .btf.vmlinux.bin ${2} } |