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.\" Copyright (c) 2022 Christos Margiolis <christos@FreeBSD.org>
.\" 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
.\" 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 AUTHOR 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 AUTHOR 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.
.\"
.\" $FreeBSD$
.\"
.Dd October 01, 2022
.Dt DTRACE_KINST 4
.Os
.Sh NAME
.Nm dtrace_kinst
.Nd a DTrace provider for tracing arbitrary instructions in a given kernel
function.
.Sh SYNOPSIS
kinst::<function>:<instruction>
.Sh DESCRIPTION
.Pp
The DTrace
.Nm kinst
provider allows the user to trace any instruction in a given kernel function.
<function> corresponds to the function to be traced, and <instruction> is the
offset to the specific instruction, and can be obtained from the function's
disassembly using
.Xr kgdb 1 .
.Pp
.Nm kinst
creates probes on-demand, meaning it searches for and parses the function's
instructions each time
.Xr dtrace 1
is run, and not at module load time. This is in contrast to FBT's load-time
parsing, since
.Nm kinst
can potentially create thousands of probes for just a single function, instead
of up to two (entry and return) in the case of FBT.
.Sh EXAMPLES
.Pp
Find the offset to the third instruction in
.Fn vm_fault
and trace it:
.Bd -literal -offset indent
# kgdb
(kgdb) disas /r vm_fault
Dump of assembler code for function vm_fault:
0xffffffff80876df0 <+0>: 55 push %rbp
0xffffffff80876df1 <+1>: 48 89 e5 mov %rsp,%rbp
0xffffffff80876df4 <+4>: 41 57 push %r15
# dtrace -n 'kinst::vm_fault:4'
.Ed
.Pp
Trace all instructions in
.Fn amd64_syscall :
.Bd -literal -offset indent
# dtrace -n 'kinst::amd64_syscall:'
.Ed
.Sh IMPLEMENTATION NOTES
The provider is currently implemented only for amd64.
.Sh SEE ALSO
.Xr dtrace 1 ,
.Xr kgdb 1
.Sh HISTORY
The
.Nm kinst
provider first appeared in
.Fx
14.0.
.Sh AUTHORS
This manual page was written by
.An Christos Margiolis Aq Mt christos@FreeBSD.org .
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