a65bee6705
The man page said dynamic allocation was required, but struct stack can be allocated in any way, including on the stack. Make this clear, and explain how to initialize the struct. While I'm here, stack_save does not require any lock. Reviewed by: markj, Pau Amma <pauamma_gundo.com> MFC after: 1 week Sponsored by: Dell EMC Isilon Differential Revision: https://reviews.freebsd.org/D34461
187 lines
5.5 KiB
Groff
187 lines
5.5 KiB
Groff
.\"
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.\" Copyright (c) 2007-2009 Robert N. M. Watson
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.\" All rights reserved.
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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(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), 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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
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.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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.\" 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 SUCH
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.\" DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd March 6, 2022
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.Dt STACK 9
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.Os
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.Sh NAME
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.Nm stack
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.Nd kernel thread stack tracing routines
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/stack.h
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.Pp
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In the kernel configuration file:
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.Cd "options DDB"
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.Cd "options STACK"
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.Pp
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.Ft struct stack *
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.Fn stack_create "int flags"
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.Ft void
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.Fn stack_destroy "struct stack *st"
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.Ft int
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.Fn stack_put "struct stack *st" "vm_offset_t pc"
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.Ft void
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.Fn stack_copy "const struct stack *src" "struct stack *dst"
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.Ft void
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.Fn stack_zero "struct stack *st"
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.Ft void
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.Fn stack_print "const struct stack *st"
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.Ft void
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.Fn stack_print_ddb "const struct stack *st"
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.Ft void
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.Fn stack_print_short "const struct stack *st"
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.Ft void
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.Fn stack_print_short_ddb "const struct stack *st"
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.Ft void
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.Fn stack_sbuf_print "struct sbuf *sb" "const struct stack *st"
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.Ft void
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.Fn stack_sbuf_print_ddb "struct sbuf *sb" "const struct stack *st"
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.Ft void
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.Fn stack_save "struct stack *st"
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.Ft int
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.Fn stack_save_td "struct stack *st" "struct thread *td"
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.Sh DESCRIPTION
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The
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.Nm
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KPI allows querying of kernel stack trace information and the automated
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generation of kernel stack trace strings for the purposes of debugging and
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tracing.
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To use the KPI, at least one of
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.Cd "options DDB"
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and
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.Cd "options STACK"
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must be compiled into the kernel.
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.Pp
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Each stack trace is described by a
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.Vt "struct stack" .
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It can be declared in the usual ways, including on the stack, and optionally
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initialized with
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.Fn stack_zero ,
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though this is not necessary before saving a trace.
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It can also be dynamically allocated with
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.Fn stack_create .
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The
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.Ar flags
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argument is passed to
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.Xr malloc 9 .
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This dynamic allocation must be freed with
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.Fn stack_destroy .
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.Pp
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A trace of the current thread's kernel call stack may be captured using
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.Fn stack_save .
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.Fn stack_save_td
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can be used to capture the kernel stack of a caller-specified thread.
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Callers of
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.Fn stack_save_td
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must own the thread lock of the specified thread,
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and the thread's stack must not be swapped out.
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.Fn stack_save_td
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can capture the kernel stack of a running thread, though note that this is
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not implemented on all platforms.
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If the thread is running, the caller must also hold the process lock for the
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target thread.
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.Pp
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.Fn stack_print
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and
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.Fn stack_print_short
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may be used to print a stack trace using the kernel
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.Xr printf 9 ,
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and may sleep as a result of acquiring
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.Xr sx 9
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locks in the kernel linker while looking up symbol names.
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In locking-sensitive environments, the unsynchronized
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.Fn stack_print_ddb
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and
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.Fn stack_print_short_ddb
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variants may be invoked.
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This function bypasses kernel linker locking, making it usable in
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.Xr ddb 4 ,
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but not in a live system where linker data structures may change.
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.Pp
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.Fn stack_sbuf_print
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may be used to construct a human-readable string, including conversion (where
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possible) from a simple kernel instruction pointer to a named symbol and
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offset.
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The argument
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.Ar sb
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must be an initialized
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.Dv struct sbuf
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as described in
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.Xr sbuf 9 .
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This function may sleep if an auto-extending
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.Dv struct sbuf
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is used, or due to kernel linker locking.
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In locking-sensitive environments, such as
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.Xr ddb 4 ,
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the unsynchronized
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.Fn stack_sbuf_print_ddb
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variant may be invoked to avoid kernel linker locking; it should be used with
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a fixed-length sbuf.
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.Pp
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The utility functions
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.Nm stack_zero ,
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.Nm stack_copy ,
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and
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.Nm stack_put
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may be used to manipulate stack data structures directly.
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.Sh RETURN VALUES
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.Fn stack_put
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returns 0 on success.
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Otherwise the
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.Dv struct stack
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does not contain space to record additional frames, and a non-zero value is
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returned.
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.Pp
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.Fn stack_save_td
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returns 0 when the stack capture was successful and a non-zero error number
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otherwise.
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In particular,
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.Er EBUSY
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is returned if the thread was running in user mode at the time that the
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capture was attempted, and
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.Er EOPNOTSUPP
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is returned if the operation is not implemented.
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.Sh SEE ALSO
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.Xr ddb 4 ,
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.Xr printf 9 ,
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.Xr sbuf 9 ,
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.Xr sx 9
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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function suite was created by
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.An Antoine Brodin .
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.Nm
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was extended by
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.An Robert Watson
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for general-purpose use outside of
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.Xr ddb 4 .
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