mirror of
git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs.git
synced 2026-11-09 11:00:49 +01:00
Fangrui Song
90ceddcb49
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. Fixes:df786c9b94("bpf: Force .BTF section start to zero when dumping from vmlinux") Fixes:cb0cc635c7("powerpc: Include .BTF section") Reported-by: Nathan Chancellor <[email protected]> Signed-off-by: Fangrui Song <[email protected]> Signed-off-by: Daniel Borkmann <[email protected]> Tested-by: Stanislav Fomichev <[email protected]> Tested-by: Andrii Nakryiko <[email protected]> Reviewed-by: Stanislav Fomichev <[email protected]> Reviewed-by: Kees Cook <[email protected]> Acked-by: Andrii Nakryiko <[email protected]> Acked-by: Michael Ellerman <[email protected]> (powerpc) Link: https://github.com/ClangBuiltLinux/linux/issues/871 Link: https://lore.kernel.org/bpf/[email protected]