xref: /openbsd-src/gnu/lib/libexecinfo/backtrace.3 (revision 55e684b42dc5507fa83a4fed61faa97ce984bbf7)

.\"	$OpenBSD: backtrace.3,v 1.3 2021/06/11 19:36:00 jmc Exp $
.\"
.\" Copyright (c) 2021 Todd Mortimer <mortimer@openbsd.org>
.\" Copyright (c) 2012 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Christos Zoulas
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: June 11 2021 $
.Dt BACKTRACE 3
.Os
.Sh NAME
.Nm backtrace ,
.Nm backtrace_symbols ,
.Nm backtrace_symbols_fd ,
.Nm backtrace_symbols_fmt ,
.Nm backtrace_symbols_fd_fmt
.Nd fill in the backtrace of the currently executing thread
.Sh SYNOPSIS
.In execinfo.h
.Ft size_t
.Fn backtrace "void **addrlist" "size_t len"
.Ft "char **"
.Fn backtrace_symbols "void * const *addrlist" "size_t len"
.Ft int
.Fn backtrace_symbols_fd "void * const *addrlist" "size_t len" "int fd"
.Ft "char **"
.Fn backtrace_symbols_fmt "void * const *addrlist" "size_t len" "const char *fmt"
.Ft int
.Fn backtrace_symbols_fd_fmt "void * const *addrlist" "size_t len" "int fd" "const char *fmt"
.Sh DESCRIPTION
The
.Fn backtrace
function places into the array pointed by
.Fa addrlist
the array of the values of the program counter for each frame called up to
.Fa len
frames.
The number of frames found (which can be fewer than
.Fa len )
is returned.
.Pp
The
.Fn backtrace_symbols_fmt
function takes an array of previously filled addresses from
.Fn backtrace
in
.Fa addrlist
of
.Fa len
elements, and uses
.Fa fmt
to format them.
The formatting characters available are:
.Bl -tag -width a -offset indent
.It Dv a
The numeric address of each element as would be printed using %p.
.It Dv n
The name of the nearest function symbol (smaller than the address element)
as determined by
.Xr dladdr 3
.It Dv d
The difference of the symbol address and the address element printed
using 0x%tx.
.It Dv D
The difference of the symbol address and the address element printed using
+0x%tx if non-zero, or nothing if zero.
.It Dv f
The filename of the symbol as determined by
.Xr dladdr 3 .
.El
.Pp
The array of formatted strings is returned as a contiguous memory address which
can be freed by a single
.Xr free 3 .
.Pp
The
.Fn backtrace_symbols
function is equivalent of calling
.Fn backtrace_symbols_fmt
with a format argument of
.Dq "%a <%n%D> at %f"
.Pp
The
.Fn backtrace_symbols_fd
and
.Fn backtrace_symbols_fd_fmt
are similar to the non _fd named functions, only instead of returning
an array of strings, they print a new-line separated array of strings in
fd, and return
.Dv 0
on success and
.Dv \-1
on failure.
.Sh RETURN VALUES
The
.Fn backtrace
function returns the number of elements that were filled in the backtrace.
The
.Fn backtrace_symbols
and
.Fn backtrace_symbols_fmt
return a string array on success, and
.Dv NULL
on failure, setting
.Va errno .
.Sh SEE ALSO
.Xr dladdr 3
.Sh HISTORY
The
.Fn backtrace
library of functions first appeared in
.Nx 7.0
and was imported into
.Ox 7.0 .
.Sh BUGS
.Bl -enum
.It
Only unwinding with libunwind is supported.
On architectures without libunwind the
.Fn backtrace
function simply returns 0.
.It
Since
.Xr dladdr 3
only deals with dynamic symbols, local symbols from the main
portion of the program are not printed.
.El