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No functional change (in program code). Additional DWARF metadata is generated in the .eh_frame section. Also, it is now a compile-time requirement that machine/asm.h ENTRY() and END() macros are paired. (This is subject to ongoing discussion and may change.) This DWARF metadata allows llvm-libunwind to unwind program stacks when the program is executing the function. The goal is to collect accurate userspace stacktraces when programs have entered syscalls. (The motivation for "Call Frame Information," or CFI for short -- not to be confused with Control Flow Integrity -- is to sufficiently annotate assembly functions such that stack unwinders can unwind out of the local frame without the requirement of a dedicated framepointer register; i.e., -fomit-frame-pointer. This is necessary for C++ exception handling or collecting backtraces.) For the curious, a more thorough description of the metadata and some examples may be found at [1] and documentation at [2]. You can also look at 'cc -S -o - foo.c | less' and search for '.cfi_' to see the CFI directives generated by your C compiler. [1]: https://www.imperialviolet.org/2017/01/18/cfi.html [2]: https://sourceware.org/binutils/docs/as/CFI-directives.html Reviewed by: emaste, kib (with reservations) Differential Revision: https://reviews.freebsd.org/D22122
113 lines
3.6 KiB
C
113 lines
3.6 KiB
C
/*-
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* SPDX-License-Identifier: BSD-3-Clause
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*
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* Copyright (c) 1990 The Regents of the University of California.
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* All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* William Jolitz.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* from: @(#)DEFS.h 5.1 (Berkeley) 4/23/90
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* $FreeBSD$
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*/
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#ifndef _MACHINE_ASM_H_
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#define _MACHINE_ASM_H_
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#include <sys/cdefs.h>
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#ifdef PIC
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#define PIC_PLT(x) x@PLT
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#define PIC_GOT(x) x@GOTPCREL(%rip)
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#else
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#define PIC_PLT(x) x
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#endif
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/*
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* CNAME and HIDENAME manage the relationship between symbol names in C
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* and the equivalent assembly language names. CNAME is given a name as
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* it would be used in a C program. It expands to the equivalent assembly
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* language name. HIDENAME is given an assembly-language name, and expands
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* to a possibly-modified form that will be invisible to C programs.
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*/
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#define CNAME(csym) csym
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#define HIDENAME(asmsym) .asmsym
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#define _START_ENTRY .text; .p2align 4,0x90
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#define _ENTRY(x) _START_ENTRY; \
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.globl CNAME(x); .type CNAME(x),@function; CNAME(x):; \
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.cfi_startproc
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#ifdef PROF
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#define ALTENTRY(x) _ENTRY(x); \
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pushq %rbp; \
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.cfi_def_cfa_offset 16; \
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.cfi_offset %rbp, -16; \
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movq %rsp,%rbp; \
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call PIC_PLT(HIDENAME(mcount)); \
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popq %rbp; \
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.cfi_restore %rbp; \
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.cfi_def_cfa_offset 8; \
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jmp 9f
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#define ENTRY(x) _ENTRY(x); \
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pushq %rbp; \
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.cfi_def_cfa_offset 16; \
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.cfi_offset %rbp, -16; \
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movq %rsp,%rbp; \
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call PIC_PLT(HIDENAME(mcount)); \
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popq %rbp; \
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.cfi_restore %rbp; \
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.cfi_def_cfa_offset 8; \
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9:
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#else
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#define ALTENTRY(x) _ENTRY(x)
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#define ENTRY(x) _ENTRY(x)
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#endif
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#define END(x) .size x, . - x; .cfi_endproc
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/*
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* WEAK_REFERENCE(): create a weak reference alias from sym.
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* The macro is not a general asm macro that takes arbitrary names,
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* but one that takes only C names. It does the non-null name
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* translation inside the macro.
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*/
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#define WEAK_REFERENCE(sym, alias) \
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.weak CNAME(alias); \
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.equ CNAME(alias),CNAME(sym)
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#define RCSID(x) .text; .asciz x
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#undef __FBSDID
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#if !defined(STRIP_FBSDID)
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#define __FBSDID(s) .ident s
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#else
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#define __FBSDID(s) /* nothing */
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#endif /* !STRIP_FBSDID */
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#endif /* !_MACHINE_ASM_H_ */
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