160 lines
4.7 KiB
Groff
160 lines
4.7 KiB
Groff
.\" $NetBSD: backtrace.3,v 1.9 2016/10/31 07:37:10 pgoyette Exp $
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.\"
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.\" Copyright (c) 2012 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Christos Zoulas
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd November 5, 2015
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.Dt BACKTRACE 3
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.Os
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.Sh NAME
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.Nm backtrace
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.Nd fill in the backtrace of the currently executing thread
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.Sh LIBRARY
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.Lb libexecinfo
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.Sh SYNOPSIS
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.In execinfo.h
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.Ft size_t
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.Fn backtrace "void **addrlist" "size_t len"
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.Ft "char **"
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.Fn backtrace_symbols "void * const *addrlist" "size_t len"
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.Ft int
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.Fn backtrace_symbols_fd "void * const *addrlist" "size_t len" "int fd"
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.Ft "char **"
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.Fn backtrace_symbols_fmt "void * const *addrlist" "size_t len" "const char *fmt"
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.Ft int
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.Fn backtrace_symbols_fd_fmt "void * const *addrlist" "size_t len" "int fd" "const char *fmt"
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.Sh DESCRIPTION
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The
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.Fn backtrace
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function places into the array pointed by
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.Fa addrlist
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the array of the values of the program counter for each frame called up to
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.Fa len
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frames.
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The number of frames found (which can be fewer than
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.Fa len )
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is returned.
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.Pp
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The
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.Fn backtrace_symbols_fmt
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function takes an array of previously filled addresses from
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.Fn backtrace
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in
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.Fa addrlist
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of
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.Fa len
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elements, and uses
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.Fa fmt
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to format them.
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The formatting characters available are:
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.Bl -tag -width a -offset indent
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.It Dv a
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The numeric address of each element as would be printed using %p.
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.It Dv n
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The name of the nearest function symbol (smaller than the address element)
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as determined by
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.Xr dladdr 3
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if the symbol was dynamic, or looked up in the executable if static and
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the /proc filesystem is available to determine the executable path.
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.It Dv d
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The difference of the symbol address and the address element printed
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using 0x%tx.
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.It Dv D
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The difference of the symbol address and the address element printed using
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+0x%tx if non-zero, or nothing if zero.
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.It Dv f
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The filename of the symbol as determined by
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.Xr dladdr 3 .
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.El
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.Pp
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The array of formatted strings is returned as a contiguous memory address which
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can be freed by a single
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.Xr free 3 .
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.Pp
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The
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.Fn backtrace_symbols
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function is equivalent of calling
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.Fn backtrace_symbols_fmt
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with a format argument of
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.Dq "%a <%n%D> at %f"
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.Pp
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The
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.Fn backtrace_symbols_fd
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and
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.Fn backtrace_symbols_fd_fmt
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are similar to the non _fd named functions, only instead of returning
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an array of strings, they print a new-line separated array of strings in
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fd, and return
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.Dv 0
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on success and
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.Dv \-1
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on failure.
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.Sh RETURN VALUES
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The
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.Fn backtrace
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function returns the number of elements that were filled in the backtrace.
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The
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.Fn backtrace_symbols
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and
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.Fn backtrace_symbols_fmt
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return a string array on success, and
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.Dv NULL
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on failure, setting
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.Va errno .
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Diagnostic output may also be produced by the ELF symbol lookup functions.
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.Sh SEE ALSO
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.Xr dladdr 3 ,
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.Xr elf 3
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.Sh HISTORY
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The
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.Fn backtrace
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library of functions first appeared in
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.Nx 7.0 .
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.Sh BUGS
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.Bl -enum
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.It
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Errors should not be printed but communicated to the caller differently.
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.It
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Because these functions use
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.Xr elf 3
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this is a separate library instead of being part of libc/libutil
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so that no library dependencies are introduced.
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.It
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The Linux versions of the functions (there are no _fmt variants) use
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.Ft int
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instead of
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.Ft size_t
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arguments.
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.It
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Since
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.Xr dladdr 3
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only deals with dynamic symbols, we need to find the symbols from the main
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portion of the program.
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For that we need to locate the executable, and we use procfs for
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finding it, which is not portable.
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.El
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