[PATCH bpf] bpf: Support llvm-objcopy and llvm-objdump for vmlinux BTF
From: Fangrui Song <hidden>
Date: 2020-03-17 01:17:00
Also in:
bpf
Subsystem:
kernel build + files below scripts/ (unless maintained elsewhere), the rest · Maintainers:
Nathan Chancellor, Nicolas Schier, Linus Torvalds
Simplify gen_btf logic to make it work with llvm-objcopy and
llvm-objdump. We just need to retain one section .BTF. To do so, we can
use a simple objcopy --only-section=.BTF instead of jumping all the
hoops via an architecture-less binary file.
We use a dd comment to change the e_type field in the ELF header from
ET_EXEC to ET_REL so that .btf.vmlinux.bin.o will be accepted by lld.
Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux")
Cc: Stanislav Fomichev <redacted>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reported-by: Nathan Chancellor <redacted>
Link: https://github.com/ClangBuiltLinux/linux/issues/871
Signed-off-by: Fangrui Song <redacted>
---
scripts/link-vmlinux.sh | 13 ++-----------
1 file changed, 2 insertions(+), 11 deletions(-)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index dd484e92752e..84be8d7c361d 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh@@ -120,18 +120,9 @@ gen_btf() info "BTF" ${2} vmlinux_link ${1} - LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} - # dump .BTF section into raw binary file to link with final vmlinux - bin_arch=$(LANG=C ${OBJDUMP} -f ${1} | grep architecture | \ - cut -d, -f1 | cut -d' ' -f2) - bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \ - awk '{print $4}') - ${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} + # Extract .BTF section, change e_type to ET_REL, to link with final vmlinux + ${OBJCOPY} --only-section=.BTF ${1} ${2} && printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 } # Create ${2} .o file with all symbols from the ${1} object file
--
2.25.1.481.gfbce0eb801-goog