From da5fb18225b49b97bb37c51bcbbb2990a507c364 Mon Sep 17 00:00:00 2001 From: Stanislav Fomichev Date: Wed, 27 Nov 2019 08:14:10 -0800 Subject: bpf: Support pre-2.25-binutils objcopy for vmlinux BTF If vmlinux BTF generation fails, but CONFIG_DEBUG_INFO_BTF is set, .BTF section of vmlinux is empty and kernel will prohibit BPF loading and return "in-kernel BTF is malformed". --dump-section argument to binutils' objcopy was added in version 2.25. When using pre-2.25 binutils, BTF generation silently fails. Convert to --only-section which is present on pre-2.25 binutils. Documentation/process/changes.rst states that binutils 2.21+ is supported, not sure those standards apply to BPF subsystem. v2: * exit and print an error if gen_btf fails (John Fastabend) v3: * resend with Andrii's Acked-by/Tested-by tags Fixes: 341dfcf8d78ea ("btf: expose BTF info through sysfs") Signed-off-by: Stanislav Fomichev Signed-off-by: Alexei Starovoitov Tested-by: Andrii Nakryiko Acked-by: Andrii Nakryiko Cc: John Fastabend Link: https://lore.kernel.org/bpf/20191127161410.57327-1-sdf@google.com --- scripts/link-vmlinux.sh | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'scripts') diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh index 06495379fcd8..2998ddb323e3 100755 --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -127,7 +127,8 @@ gen_btf() cut -d, -f1 | cut -d' ' -f2) bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \ awk '{print $4}') - ${OBJCOPY} --dump-section .BTF=.btf.vmlinux.bin ${1} 2>/dev/null + ${OBJCOPY} --set-section-flags .BTF=alloc -O binary \ + --only-section=.BTF ${1} .btf.vmlinux.bin 2>/dev/null ${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \ --rename-section .data=.BTF .btf.vmlinux.bin ${2} } @@ -253,6 +254,10 @@ btf_vmlinux_bin_o="" if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then if gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then btf_vmlinux_bin_o=.btf.vmlinux.bin.o + else + echo >&2 "Failed to generate BTF for vmlinux" + echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF" + exit 1 fi fi -- cgit v1.2.3 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