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 | 113 | gen_btf() |
| 114 | 114 | { |
| 115 | 115 | local pahole_ver |
| 116 | − local bin_arch | |
| 117 | − local bin_format | |
| 118 | − local bin_file | |
| 119 | 116 | |
| 120 | 117 | if ! [ -x "$(command -v ${PAHOLE})" ]; then |
| 121 | 118 | echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available" |
| @@ -133,17 +130,16 @@ gen_btf() · 11 unmodified lines | ||
| 133 | 130 | info "BTF" ${2} |
| 134 | 131 | LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1} |
| 135 | 132 | |
| 136 | − # dump .BTF section into raw binary file to link with final vmlinux | |
| 137 | − bin_arch=$(LANG=C ${OBJDUMP} -f ${1} | grep architecture | \ | |
| 138 | − cut -d, -f1 | cut -d' ' -f2) | |
| 139 | − bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \ | |
| 140 | − awk '{print $4}') | |
| 141 | − bin_file=.btf.vmlinux.bin | |
| 142 | − ${OBJCOPY} --change-section-address .BTF=0 \ | |
| 143 | − --set-section-flags .BTF=alloc -O binary \ | |
| 144 | − --only-section=.BTF ${1} $bin_file | |
| 145 | − ${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \ | |
| 146 | − --rename-section .data=.BTF $bin_file ${2} | |
| 133 | + # Create ${2} which contains just .BTF section but no symbols. Add | |
| 134 | + # SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all | |
| 135 | + # deletes all symbols including __start_BTF and __stop_BTF, which will | |
| 136 | + # be redefined in the linker script. Add 2>/dev/null to suppress GNU | |
| 137 | + # objcopy warnings: "empty loadable segment detected at ..." | |
| 138 | + ${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \ | |
| 139 | + --strip-all ${1} ${2} 2>/dev/null | |
| 140 | + # Change e_type to ET_REL so that it can be used to link final vmlinux. | |
| 141 | + # Unlike GNU ld, lld does not allow an ET_EXEC input. | |
| 142 | + printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 status=none | |
| 147 | 143 | } |
| 148 | 144 | |
| 149 | 145 | # Create ${2} .o file with all symbols from the ${1} object file |