148 lines
3.3 KiB
Bash
Executable File
148 lines
3.3 KiB
Bash
Executable File
#!/bin/sh
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# SPDX-License-Identifier: GPL-2.0
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# Copyright (c) 2025 Meta Platforms, Inc. and affiliates.
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#
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# This script generates BTF data for the provided ELF file.
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#
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# Kernel BTF generation involves these conceptual steps:
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# 1. pahole generates BTF from DWARF data
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# 2. resolve_btfids applies kernel-specific btf2btf
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# transformations and computes data for .BTF_ids section
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# 3. the result gets linked/objcopied into the target binary
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#
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# How step (3) should be done differs between vmlinux, and
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# kernel modules, which is the primary reason for the existence
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# of this script.
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#
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# For modules the script expects vmlinux passed in as --btf_base.
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# Generated .BTF, .BTF.base and .BTF_ids sections become embedded
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# into the input ELF file with objcopy.
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#
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# For vmlinux the input file remains unchanged and two files are produced:
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# - ${1}.btf.o ready for linking into vmlinux
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# - ${1}.BTF_ids with .BTF_ids data blob
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# This output is consumed by scripts/link-vmlinux.sh
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set -e
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usage()
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{
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echo "Usage: $0 [--btf_base <file>] <target ELF file>"
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exit 1
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}
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BTF_BASE=""
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while [ $# -gt 0 ]; do
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case "$1" in
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--btf_base)
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BTF_BASE="$2"
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shift 2
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;;
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-*)
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echo "Unknown option: $1" >&2
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usage
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;;
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*)
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break
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;;
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esac
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done
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if [ $# -ne 1 ]; then
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usage
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fi
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ELF_FILE="$1"
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shift
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is_enabled() {
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grep -q "^$1=y" ${objtree}/include/config/auto.conf
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}
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case "${KBUILD_VERBOSE}" in
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*1*)
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set -x
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;;
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esac
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gen_btf_data()
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{
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btf1="${ELF_FILE}.BTF.1"
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${PAHOLE} -J ${PAHOLE_FLAGS} \
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${BTF_BASE:+--btf_base ${BTF_BASE}} \
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--btf_encode_detached=${btf1} \
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"${ELF_FILE}"
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${RESOLVE_BTFIDS} ${RESOLVE_BTFIDS_FLAGS} \
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${BTF_BASE:+--btf_base ${BTF_BASE}} \
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--btf ${btf1} "${ELF_FILE}"
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}
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gen_btf_o()
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{
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btf_data=${ELF_FILE}.btf.o
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# Create ${btf_data} which contains just .BTF section but no symbols. Add
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# SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all
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# deletes all symbols including __start_BTF and __stop_BTF, which will
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# be redefined in the linker script.
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echo "" | ${CC} ${CLANG_FLAGS} ${KBUILD_CPPFLAGS} ${KBUILD_CFLAGS} -fno-lto -c -x c -o ${btf_data} -
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${OBJCOPY} --add-section .BTF=${ELF_FILE}.BTF \
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--set-section-flags .BTF=alloc,readonly ${btf_data}
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${OBJCOPY} --only-section=.BTF --strip-all ${btf_data}
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# Change e_type to ET_REL so that it can be used to link final vmlinux.
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# GNU ld 2.35+ and lld do not allow an ET_EXEC input.
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if is_enabled CONFIG_CPU_BIG_ENDIAN; then
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et_rel='\0\1'
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else
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et_rel='\1\0'
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fi
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printf "${et_rel}" | dd of="${btf_data}" conv=notrunc bs=1 seek=16 status=none
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}
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embed_btf_data()
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{
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${OBJCOPY} --add-section .BTF=${ELF_FILE}.BTF ${ELF_FILE}
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# a module might not have a .BTF_ids or .BTF.base section
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btf_base="${ELF_FILE}.BTF.base"
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if [ -f "${btf_base}" ]; then
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${OBJCOPY} --add-section .BTF.base=${btf_base} ${ELF_FILE}
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fi
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btf_ids="${ELF_FILE}.BTF_ids"
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if [ -f "${btf_ids}" ]; then
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${RESOLVE_BTFIDS} --patch_btfids ${btf_ids} ${ELF_FILE}
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fi
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}
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cleanup()
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{
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rm -f "${ELF_FILE}.BTF.1"
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rm -f "${ELF_FILE}.BTF"
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if [ "${BTFGEN_MODE}" = "module" ]; then
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rm -f "${ELF_FILE}.BTF.base"
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rm -f "${ELF_FILE}.BTF_ids"
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fi
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}
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trap cleanup EXIT
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BTFGEN_MODE="vmlinux"
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if [ -n "${BTF_BASE}" ]; then
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BTFGEN_MODE="module"
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fi
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gen_btf_data
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case "${BTFGEN_MODE}" in
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vmlinux)
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gen_btf_o
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;;
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module)
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embed_btf_data
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;;
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esac
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exit 0
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