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Commitsffb1b4a410("x86/unwind/orc: Add 'signal' field to ORC metadata") andfb799447ae("x86,objtool: Split UNWIND_HINT_EMPTY in two") changed the ORC format. Although ORC is internal to the kernel, it's the only way for external tools to get reliable kernel stack traces on x86-64. In particular, the drgn debugger [1] uses ORC for stack unwinding, and these format changes broke it [2]. As the drgn maintainer, I don't care how often or how much the kernel changes the ORC format as long as I have a way to detect the change. It suffices to store a version identifier in the vmlinux and kernel module ELF files (to use when parsing ORC sections from ELF), and in kernel memory (to use when parsing ORC from a core dump+symbol table). Rather than hard-coding a version number that needs to be manually bumped, Peterz suggested hashing the definitions from orc_types.h. If there is a format change that isn't caught by this, the hashing script can be updated. This patch adds an .orc_header allocated ELF section containing the 20-byte hash to vmlinux and kernel modules, along with the corresponding __start_orc_header and __stop_orc_header symbols in vmlinux. 1: https://github.com/osandov/drgn 2: https://github.com/osandov/drgn/issues/303 Fixes:ffb1b4a410("x86/unwind/orc: Add 'signal' field to ORC metadata") Fixes:fb799447ae("x86,objtool: Split UNWIND_HINT_EMPTY in two") Signed-off-by: Omar Sandoval <osandov@fb.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Josh Poimboeuf <jpoimboe@kernel.org> Link: https://lkml.kernel.org/r/aef9c8dc43915b886a8c48509a12ec1b006ca1ca.1686690801.git.osandov@osandov.com
20 lines
483 B
C
20 lines
483 B
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/* Copyright (c) Meta Platforms, Inc. and affiliates. */
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#ifndef _ORC_HEADER_H
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#define _ORC_HEADER_H
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#include <linux/types.h>
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#include <linux/compiler.h>
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#include <asm/orc_hash.h>
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/*
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* The header is currently a 20-byte hash of the ORC entry definition; see
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* scripts/orc_hash.sh.
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*/
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#define ORC_HEADER \
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__used __section(".orc_header") __aligned(4) \
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static const u8 orc_header[] = { ORC_HASH }
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#endif /* _ORC_HEADER_H */
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