From df786c9b947639aedbc7bb44b5dae2a7824af360 Mon Sep 17 00:00:00 2001 From: Stanislav Fomichev Date: Wed, 27 Nov 2019 14:57:59 -0800 Subject: 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 Signed-off-by: Daniel Borkmann Acked-by: John Fastabend Cc: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20191127225759.39923-1-sdf@google.com --- scripts/link-vmlinux.sh | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'scripts') 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} } -- cgit v1.2.3-59-g8ed1b