xref: /freebsd/share/man/man4/dtrace_kinst.4 (revision 8e95079e175854b84e57c521b34b4b52f7ae9cb1)
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25.Dd February 27, 2023
26.Dt DTRACE_KINST 4
27.Os
28.Sh NAME
29.Nm dtrace_kinst
30.Nd a DTrace provider for tracing arbitrary instructions in a given kernel function
31.Sh SYNOPSIS
32kinst::<function>:<instruction>
33.Sh DESCRIPTION
34The DTrace
35.Nm kinst
36provider allows the user to trace any instruction in a given kernel function.
37<function> corresponds to the function to be traced, and <instruction> is the
38offset to the specific instruction, and can be obtained from the function's
39disassembly using kgdb from the gdb package.
40.Pp
41.Nm kinst
42creates probes on-demand, meaning it searches for and parses the function's
43instructions each time
44.Xr dtrace 1
45is run, and not at module load time.
46This is in contrast to FBT's load-time parsing, since
47.Nm kinst
48can potentially create thousands of probes for just a single function, instead
49of up to two (entry and return) in the case of FBT.
50A result of this is that
51.Cm dtrace -l -P kinst
52will not match any probes.
53.Sh IMPLEMENTATION NOTES
54The provider is currently implemented only for amd64.
55.Sh EXAMPLES
56Find the offset corresponding to the third instruction in
57.Fn vm_fault
58and trace it, printing the contents of the RSI register:
59.Bd -literal -offset indent
60# kgdb
61(kgdb) disas /r vm_fault
62Dump of assembler code for function vm_fault:
63   0xffffffff80876df0 <+0>:     55      push   %rbp
64   0xffffffff80876df1 <+1>:     48 89 e5        mov    %rsp,%rbp
65   0xffffffff80876df4 <+4>:     41 57   push   %r15
66
67# dtrace -n 'kinst::vm_fault:4 {printf("%#x", regs[R_RSI]);}'
68  2  81500                       vm_fault:4 0x827c56000
69  2  81500                       vm_fault:4 0x827878000
70  2  81500                       vm_fault:4 0x1fab9bef0000
71  2  81500                       vm_fault:4 0xe16cf749000
72  0  81500                       vm_fault:4 0x13587c366000
73  ...
74.Ed
75.Pp
76Trace all instructions in
77.Fn amd64_syscall :
78.Bd -literal -offset indent
79# dtrace -n 'kinst::amd64_syscall:'
80.Ed
81.Sh SEE ALSO
82.Xr dtrace 1
83.Sh HISTORY
84The
85.Nm kinst
86provider first appeared in
87.Fx
8814.0.
89.Sh AUTHORS
90This manual page was written by
91.An Christos Margiolis Aq Mt christos@FreeBSD.org .
92