Simplify gen_btf logic to make it work with llvm-objcopy. The existing 'file format' and 'architecture' parsing logic is brittle and does not work with llvm-objcopy/llvm-objdump. 'file format' output of llvm-objdump>=11 will match GNU objdump, but 'architecture' (bfdarch) may not. .BTF in .tmp_vmlinux.btf is non-SHF_ALLOC. Add the SHF_ALLOC flag because it is part of vmlinux image used for introspection. C code can reference the section via linker script defined __start_BTF and __stop_BTF. This fixes a small problem that previous .BTF had the SHF_WRITE flag (objcopy -I binary -O elf* synthesized .data). Additionally, `objcopy -I binary` synthesized symbols _binary__btf_vmlinux_bin_start and _binary__btf_vmlinux_bin_stop (not used elsewhere) are replaced with more commonplace __start_BTF and __stop_BTF. Add 2>/dev/null because GNU objcopy (but not llvm-objcopy) warns "empty loadable segment detected at vaddr=0xffffffff81000000, is this intentional?" We use a dd command to change the e_type field in the ELF header from ET_EXEC to ET_REL so that lld will accept .btf.vmlinux.bin.o. Accepting ET_EXEC as an input file is an extremely rare GNU ld feature that lld does not intend to support, because this is error-prone. The output section description .BTF in include/asm-generic/vmlinux.lds.h avoids potential subtle orphan section placement issues and suppresses --orphan-handling=warn warnings.
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| @@ -113,9 +113,6 @@ vmlinux_link() · 112 unmodified lines | |||
| 113 | gen_btf() | 113 | gen_btf() |
| 114 | { | 114 | { |
| 115 | local pahole_ver | 115 | local pahole_ver |
| 116 | local bin_arch | ||
| 117 | local bin_format | ||
| 118 | local bin_file | ||
| 119 | 116 | ||
| 120 | if ! [ -x "$(command -v ${PAHOLE})" ]; then | 117 | if ! [ -x "$(command -v ${PAHOLE})" ]; then |
| 121 | echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available" | 118 | echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available" |
| @@ -133,17 +130,16 @@ gen_btf() · 11 unmodified lines | |||
| 133 | info "BTF" ${2} | 130 | info "BTF" ${2} |
| 134 | LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} | 131 | LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} |
| 135 | 132 | ||
| 136 | # dump .BTF section into raw binary file to link with final vmlinux | 133 | # Create ${2} which contains just .BTF section but no symbols. Add |
| 137 | bin_arch=$(LANG=C ${OBJDUMP} -f ${1} | grep architecture | \ | 134 | # SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all |
| 138 | cut -d, -f1 | cut -d' ' -f2) | 135 | # deletes all symbols including __start_BTF and __stop_BTF, which will |
| 139 | bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \ | 136 | # be redefined in the linker script. Add 2>/dev/null to suppress GNU |
| 140 | awk '{print $4}') | 137 | # objcopy warnings: "empty loadable segment detected at ..." |
| 141 | bin_file=.btf.vmlinux.bin | 138 | ${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \ |
| 142 | ${OBJCOPY} --change-section-address .BTF=0 \ | 139 | --strip-all ${1} ${2} 2>/dev/null |
| 143 | --set-section-flags .BTF=alloc -O binary \ | 140 | # Change e_type to ET_REL so that it can be used to link final vmlinux. |
| 144 | --only-section=.BTF ${1} $bin_file | 141 | # Unlike GNU ld, lld does not allow an ET_EXEC input. |
| 145 | ${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \ | 142 | printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 status=none |
| 146 | --rename-section .data=.BTF $bin_file ${2} | ||
| 147 | } | 143 | } |
| 148 | 144 | ||
| 149 | # Create ${2} .o file with all symbols from the ${1} object file | 145 | # Create ${2} .o file with all symbols from the ${1} object file |