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).
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| @@ -127,8 +127,9 @@ gen_btf() · 126 unmodified lines | |||
| 127 | cut -d, -f1 | cut -d' ' -f2) | 127 | cut -d, -f1 | cut -d' ' -f2) |
| 128 | bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \ | 128 | bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \ |
| 129 | awk '{print $4}') | 129 | awk '{print $4}') |
| 130 | ${OBJCOPY} --set-section-flags .BTF=alloc -O binary \ | 130 | ${OBJCOPY} --change-section-address .BTF=0 \ |
| 131 | --only-section=.BTF ${1} .btf.vmlinux.bin 2>/dev/null | 131 | --set-section-flags .BTF=alloc -O binary \ |
| 132 | --only-section=.BTF ${1} .btf.vmlinux.bin | ||
| 132 | ${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \ | 133 | ${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \ |
| 133 | --rename-section .data=.BTF .btf.vmlinux.bin ${2} | 134 | --rename-section .data=.BTF .btf.vmlinux.bin ${2} |
| 134 | } | 135 | } |