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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 <natechancellor@gmail.com> Signed-off-by: Fangrui Song <maskray@google.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Tested-by: Stanislav Fomichev <sdf@google.com> Tested-by: Andrii Nakryiko <andriin@fb.com> Reviewed-by: Stanislav Fomichev <sdf@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Acked-by: Andrii Nakryiko <andriin@fb.com> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc) Link: https://github.com/ClangBuiltLinux/linux/issues/871 Link: https://lore.kernel.org/bpf/20200318222746.173648-1-maskray@google.com
46 lines
1.1 KiB
C
46 lines
1.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Provide kernel BTF information for introspection and use by eBPF tools.
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/kobject.h>
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#include <linux/init.h>
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#include <linux/sysfs.h>
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/* See scripts/link-vmlinux.sh, gen_btf() func for details */
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extern char __weak __start_BTF[];
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extern char __weak __stop_BTF[];
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static ssize_t
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btf_vmlinux_read(struct file *file, struct kobject *kobj,
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struct bin_attribute *bin_attr,
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char *buf, loff_t off, size_t len)
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{
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memcpy(buf, __start_BTF + off, len);
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return len;
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}
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static struct bin_attribute bin_attr_btf_vmlinux __ro_after_init = {
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.attr = { .name = "vmlinux", .mode = 0444, },
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.read = btf_vmlinux_read,
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};
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static struct kobject *btf_kobj;
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static int __init btf_vmlinux_init(void)
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{
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if (!__start_BTF)
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return 0;
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btf_kobj = kobject_create_and_add("btf", kernel_kobj);
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if (!btf_kobj)
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return -ENOMEM;
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bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
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return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
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}
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subsys_initcall(btf_vmlinux_init);
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