Page MenuHomeFreeBSD
Files F156898942

D50922.id157372.diff
No OneTemporary
Actions

D50922.id157372.diff
View Options

diff --git a/share/man/man4/Makefile b/share/man/man4/Makefile
--- a/share/man/man4/Makefile
+++ b/share/man/man4/Makefile
@@ -967,6 +967,7 @@
.if ${MK_CDDL} != "no"
_dtrace_provs= dtrace_audit.4 \
+ dtrace_fbt.4 \
dtrace_io.4 \
dtrace_ip.4 \
dtrace_kinst.4 \
diff --git a/share/man/man4/dtrace_fbt.4 b/share/man/man4/dtrace_fbt.4
new file mode 100644
--- /dev/null
+++ b/share/man/man4/dtrace_fbt.4
@@ -0,0 +1,189 @@
+.\"
+.\" SPDX-License-Identifier: BSD-2-Clause
+.\"
+.\" Copyright (c) 2025 Mateusz Piotrowski <0mp@FreeBSD.org>
+.\"
+.Dd June 14, 2025
+.Dt DTRACE_FBT 4
+.Os
+.Sh NAME
+.Nm dtrace_fbt
+.Nd a DTrace provider for function boundary tracing
+.Sh SYNOPSIS
+.Sm off
+.Nm fbt Cm \&: Ar module Cm \&: Ar function Cm \&: Ar name
+.Sm on
+.Sh DESCRIPTION
+The Function Boundary Tracing
+.Pq Nm fbt
+provider instruments the entry and return of every almost every function
+in the kernel and modules.
+It will always instrument function entry,
+and it will instrument function return so long as it can find a
+.Ql ret
+instruction
+.Pq a return via a tail call is never instrumented .
+.Pp
+Users can use the
+.Nm fbt
+provider to trace most function calls.
+Refer to the
+.Sx Frame Pointer
+subsection for more details.
+.Sh IMPLEMENTATION NOTES
+The
+.Nm fbt
+probes are by definition tightly coupled to kernel code; if the code underlying
+a script changes, the script may fail to run or may produce incorrect results.
+Scripts written for one version of
+.Fx
+might not work on another,
+and almost certainly will not work on other operating systems.
+.Pp
+Individual
+.Nm fbt
+probes often do not correspond nicely to logical system events.
+For example, consider a DTrace script which prints the destination
+address of every IP packet as the kernel hands them over
+to the network card driver.
+It turns out that this is a discouragingly difficult task:
+it involves instrumenting at least four different functions in different parts
+of the IPv4 and IPv6 code.
+Users should try available
+.Xr dtrace 1
+providers first
+.Po such as
+.Xr dtrace_ip 4 Pc ,
+before implementing a custom script with the
+.Nm fbt
+provider.
+Another potential solution is adding statically-defined tracing probes
+.Pq Xr SDT 9 .
+.Pp
+The
+.Nm fbt
+provider cannot attach to functions inside DTrace provider modules.
+.Ss Frame Pointer
+Inline functions are not instrumentable by
+.Nm fbt
+as they lack a frame pointer.
+A developer might explicitly disable inlining by adding the
+.Ql __noinline
+attribute to a function definition,
+but of course this requires a recompile of the kernel.
+Building the kernel with
+.Fl fno-omit-frame-pointer
+is another way of preserving frame pointers.
+Note, that sometimes compilers will omit frame pointer usage in leaf functions
+even when configured with
+.Fl fno-omit-frame-pointer .
+.Pp
+Function returns via a tail call are also not instrumentable by
+.Nm fbt .
+As a result,
+a function might have an entry probe
+and a mix of instrumented and uninstrumentable returns.
+.Pp
+Use
+.Xr dtrace_kinst 4
+to trace arbitrary instructions inside kernel functions
+and work around some of the
+.Nm fbt
+limitations.
+.Sh EXAMPLES
+.Ss Example 1 : No Listing Available FBT Probes
+.Bd -literal -offset 2n
+.No # Nm dtrace Fl l Fl P Cm fbt
+ ID PROVIDER MODULE FUNCTION NAME
+[...]
+31868 fbt kernel hammer_time entry
+31869 fbt kernel hammer_time return
+[...]
+.Ed
+.Ss Example 2 : No Counting Kernel Slab Memory Allocation by Function
+.Bd -literal -offset 2n
+.No # Nm dtrace Fl n Cm 'fbt::kmem*:entry { @[probefunc] = count(); }'
+dtrace: description 'fbt::kmem*:entry ' matched 47 probes
+.Ic ^C
+ kmem_alloc_contig 1
+ kmem_alloc_contig_domainset 1
+ kmem_cache_reap_active 1
+ kmem_alloc_contig_pages 2
+ kmem_free 2
+ kmem_std_destructor 19
+ kmem_std_constructor 26
+ kmem_cache_free 151
+ kmem_cache_alloc 181
+.Ed
+.Ss Example 3 : No Counting Kernel Slab Memory Allocation by Calling Function
+.Bd -literal -offset 2n
+.No # Nm dtrace Fl q Fl n Cm 'fbt::kmem*:entry { @[caller] = count(); } END { printa("%40a %@16d\en", @); }'
+.Ic ^C
+ kernel`contigmalloc+0x33 1
+ kernel`free+0xd3 1
+ kernel`kmem_alloc_contig+0x29 1
+kernel`kmem_alloc_contig_domainset+0x19a 1
+ zfs.ko`arc_reap_cb_check+0x16 1
+.Ed
+.Ss Example 4 : No Counting Kernel malloc()'s by Calling Function
+.Bd -literal -offset 2n
+.No # Nm dtrace Fl q Fl n Cm 'fbt::malloc:entry { @[caller] = count(); } END { printa("%45a %@16d\en", @); }'
+.Ic ^C
+ kernel`devclass_get_devices+0xa8 1
+ kernel`sys_ioctl+0xb7 1
+ dtrace.ko`dtrace_ioctl+0x15c1 1
+ dtrace.ko`dtrace_ioctl+0x972 2
+ dtrace.ko`dtrace_dof_create+0x35 2
+ kernel`kern_poll_kfds+0x2f0 4
+ kernel`kern_poll_kfds+0x28a 19
+.Ed
+.Ss Example 5 : No Counting Kernel malloc()'s by Kernel Stack Trace
+.Bd -literal -offset 2n
+.No # Nm dtrace Fl q Fl n Cm 'fbt::malloc:entry { @[stack()] = count(); }'
+.Ic ^C
+ dtrace.ko`dtrace_dof_create+0x35
+ dtrace.ko`dtrace_ioctl+0x827
+ kernel`devfs_ioctl+0xd1
+ kernel`VOP_IOCTL_APV+0x2a
+ kernel`vn_ioctl+0xb6
+ kernel`devfs_ioctl_f+0x1e
+ kernel`kern_ioctl+0x286
+ kernel`sys_ioctl+0x12f
+ kernel`amd64_syscall+0x169
+ kernel`0xffffffff81092b0b
+ 2
+.Ed
+.Ss Example 6 : No Summarizing vmem_alloc()'s by Arena Name and Size Distribution
+.Bd -literal -offset 2n
+.No # Nm dtrace Fl n Cm 'fbt::vmem_alloc:entry { @[args[0]->vm_name] = quantize(arg1); }'
+dtrace: description 'fbt::vmem_alloc:entry ' matched 1 probe
+.Ic ^C
+
+ kernel arena dom
+ value ------------- Distribution ------------- count
+ 2048 | 0
+ 4096 |@@@@@@@@@@@@@@@@@@@@@@@@@@@ 4
+ 8192 |@@@@@@@@@@@@@ 2
+ 16384 | 0
+
+.Ed
+.Sh SEE ALSO
+.Xr dtrace 1
+.Rs
+.%A Brendan Gregg
+.%A Jim Mauro
+.%B DTrace: Dynamic Tracing in Oracle Solaris, Mac OS X and FreeBSD
+.%I Prentice Hall
+.%P pp. 898\(en903
+.%D 2011
+.%U https://www.brendangregg.com/dtracebook/
+.Re
+.Rs
+.%B The illumos Dynamic Tracing Guide
+.%O Chapter fbt Provider
+.%D 2008
+.%U https://illumos.org/books/dtrace/chp-fbt.html#chp-fbt
+.Re
+.Sh AUTHORS
+This manual page was written by
+.An Mateusz Piotrowski Aq Mt 0mp@FreeBSD.org .

File Metadata

Mime Type
text/plain
Expires
Mon, May 18, 4:50 AM (7 h, 43 m)
Storage Engine
blob
Storage Format
Raw Data
Storage Handle
33213224
Default Alt Text
D50922.id157372.diff (7 KB)

Event Timeline