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Introduce ltrace(1). This tool works with ld.so to inject utrace record for
each plt call, allowing to trace a binary linked against shared library at the
public function call level.

To do so, ltrace(1) sets up some environment variables to enable plt tracing
in ld.so, and invokes ktrace(2) for utrace events. ld.so will force lazy
binding and will send an utrace record in the plt resolver, without updating
the plt.

Minimal filtering capabilities are provided, inspired by Solaris' truss -u,
to limit tracing to libraries and/or symbol names. Non-traced libraries and
symbols will have the regular resolver processing, with the expected plt
update.

"Get it in" deraadt

.\"	$OpenBSD: ltrace.1,v 1.1 2013/06/01 09:57:58 miod Exp $
.\"
.\" Copyright (c) 2013 Miodrag Vallat.
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.\" Copyright (c) 1990, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" 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
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.\"    may be used to endorse or promote products derived from this software
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.\"
.\"	from: @(#)ktrace.1	8.1 (Berkeley) 6/6/93
.\"
.Dd $Mdocdate: June 1 2013 $
.Dt LTRACE 1
.Os
.Sh NAME
.Nm ltrace
.Nd shared library function call tracer
.Sh SYNOPSIS
.Nm ltrace
.Op Fl ai
.Op Fl f Ar trfile
.Op Fl u Ar trspec
.Ar command
.Sh DESCRIPTION
.Nm ltrace
enables shared library function calls issued by the specified processes
to be traced using the
.Xr utrace 2
user tracing facility.
By default, call trace data is logged to the file
.Pa ktrace.out ,
unless overridden by the
.Fl f
option.
Each function call is traced as a pair of
.Dv KTRFAC_USER
entries;
the first entry contains the shared library containing the symbol being
called, and the second entry contains the symbol name.
.Pp
Once tracing is enabled on a process, trace data will be logged until
either the process exits or the trace point is cleared with
.Xr ktrace 1 .
A traced process can generate enormous amounts of log data quickly;
it is strongly suggested that users memorize how to disable tracing before
attempting to trace a process.
The following command is sufficient to disable tracing on all user owned
processes, and, if executed by root, all processes:
.Pp
.Dl $ ktrace -C
.Pp
The trace file is not human-readable; use
.Xr kdump 1
to decode it.
.Pp
The options are as follows:
.Bl -tag -width 9n
.It Fl a
Append to the trace file instead of recreating it.
.It Fl f Ar trfile
Log trace records to
.Ar trfile
instead of
.Pa ktrace.out .
.It Fl i
Inherit; pass the trace flags to all future children of the designated
processes.
.It Ar command
Execute
.Ar command
with the specified trace flags.
.It Fl u Ar trspec
Restrict the trace to a list of shared objects and/or function names, as
specified by the
.Ar trspec
argument.
The trace specification is a comma-separated list of library names,
followed by a colon
.Pq : , and a comma-separated list of function names.
Each list can be empty.
Each list member may end up with a star
.Pq *
to only match the beginning of a name.
A leading bang at the beginning of a list turns it into a rejection list,
causing all unmatched names to be traced.
Library names are compared without their version number and
.Sq .so
suffix.
.El
.Sh FILES
.Bl -tag -width ktrace.out -compact
.It Pa ktrace.out
default ltrace dump file
.El
.Sh EXAMPLES
Trace all shared library function calls from
.Xr wc 1
reading the message of the day:
.Dl $ ltrace wc -lh /etc/motd
.Pp
Trace only the shared library function calls in
.Pa libutil.so :
.Dl $ ltrace -u libutil wc -lh /etc/motd
.Pp
Trace all the shared library function calls but those in
.Pa libc.so :
.Dl $ ltrace -u \(dq!libc\(dq wc -lh /etc/motd
.Pp
Trace all the shared library function calls which name start in
.Pq fmt :
.Dl $ ltrace -u \(dq:fmt*\(dq wc -lh /etc/motd
.Sh SEE ALSO
.Xr kdump 1 ,
.Xr ktrace 1 ,
.Xr ktrace 2 ,
.Xr utrace 2