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d1091c7fa3
The BUG() macro's use of __builtin_unreachable() via the unreachable() macro tells gcc that the instruction is a dead end, and that it's safe to assume the current code path will not execute past the previous instruction. On x86, the BUG() macro is implemented with the 'ud2' instruction. When objtool's branch analysis sees that instruction, it knows the current code path has come to a dead end. Peter Zijlstra has been working on a patch to change the WARN macros to use 'ud2'. That patch will break objtool's assumption that 'ud2' is always a dead end. Generally it's best for objtool to avoid making those kinds of assumptions anyway. The more ignorant it is of kernel code internals, the better. So create a more generic way for objtool to detect dead ends by adding an annotation to the unreachable() macro. The annotation stores a pointer to the end of the unreachable code path in an '__unreachable' section. Objtool can read that section to find the dead ends. Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/41a6d33971462ebd944a1c60ad4bf5be86c17b77.1487712920.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
44 lines
1.3 KiB
C
44 lines
1.3 KiB
C
/*
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* Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef _ARCH_H
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#define _ARCH_H
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#include <stdbool.h>
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#include "elf.h"
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#define INSN_FP_SAVE 1
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#define INSN_FP_SETUP 2
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#define INSN_FP_RESTORE 3
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#define INSN_JUMP_CONDITIONAL 4
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#define INSN_JUMP_UNCONDITIONAL 5
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#define INSN_JUMP_DYNAMIC 6
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#define INSN_CALL 7
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#define INSN_CALL_DYNAMIC 8
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#define INSN_RETURN 9
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#define INSN_CONTEXT_SWITCH 10
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#define INSN_NOP 11
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#define INSN_OTHER 12
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#define INSN_LAST INSN_OTHER
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int arch_decode_instruction(struct elf *elf, struct section *sec,
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unsigned long offset, unsigned int maxlen,
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unsigned int *len, unsigned char *type,
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unsigned long *displacement);
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#endif /* _ARCH_H */
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