git: f622f1f7d5 - main - 2023Q1 kinst DTrace status report submission

The branch main has been updated by pauamma:

URL: https://cgit.FreeBSD.org/doc/commit/?id=f622f1f7d54f5dc72835e6fd85786a1e19d21ce3

commit f622f1f7d54f5dc72835e6fd85786a1e19d21ce3
Author:     Christos Margiolis <[email protected]>
AuthorDate: 2023-03-04 17:57:43 +0000
Commit:     Pau Amma <[email protected]>
CommitDate: 2023-03-09 20:37:27 +0000

    2023Q1 kinst DTrace status report submission
    
    Lightly copyedited from emailed original, and reformatted as 1 sentence
    per line.
    
    Approved by:    carlavilla
---
 .../report-2023-01-2023-03/kinst_2023q1.adoc       | 71 ++++++++++++++++++++++
 1 file changed, 71 insertions(+)

diff --git a/website/content/en/status/report-2023-01-2023-03/kinst_2023q1.adoc b/website/content/en/status/report-2023-01-2023-03/kinst_2023q1.adoc
new file mode 100644
index 0000000000..743081d850
--- /dev/null
+++ b/website/content/en/status/report-2023-01-2023-03/kinst_2023q1.adoc
@@ -0,0 +1,71 @@
+=== Improve the kinst DTrace provider
+
+Links: +
+link:https://reviews.freebsd.org/D38825[libdtrace: implement inline function tracing] URL: link:https://reviews.freebsd.org/D38825[https://reviews.freebsd.org/D38825] +
+link:https://reviews.freebsd.org/D38732[dtrace(1): add -d flag to dump D script post-dt_sugar] URL: link:https://reviews.freebsd.org/D38732[https://reviews.freebsd.org/D38732]
+
+Contact: Christos Margiolis <[email protected]> +
+Contact: Mark Johnston <[email protected]>
+
+kinst is a new DTrace provider created by christos@ and markj@ that allows for
+arbitrary instruction tracing in a kernel function. kinst has been added to the
+base system in FreeBSD 14.0.
+
+link:https://www.freebsd.org/status/report-2022-07-2022-09/#_dtrace_instruction_level_dynamic_tracing[The 2022Q3 status report gives a brief introduction to kinst.]
+We're now working on inline function tracing (see review D38825 above) -- a much-requested DTrace feature -- by using kernel DWARF and ELF info to find the call sites of each inline copy and use that information to transform D syntax by turning kinst probes of the form:
+
+....
+	kinst::<inline_func>:<entry/return>
+....
+
+To:
+
+....
+	kinst::<caller_func1>:<offset>
+	kinst::<caller_func2>:<offset>
+	...
+....
+
+For example:
+
+....
+	# dtrace -dn 'kinst::cam_iosched_has_more_trim:entry { printf("\t%d\t%s", pid, execname); }'
+	dtrace:::ERROR
+	{
+		((self->%error) = 0x1);
+	}
+
+	kinst::cam_iosched_get_trim:13
+	{
+		printf("\t%d\t%s", pid, execname);
+	}
+
+	kinst::cam_iosched_next_bio:13
+	{
+		printf("\t%d\t%s", pid, execname);
+	}
+
+	kinst::cam_iosched_schedule:40
+	{
+		printf("\t%d\t%s", pid, execname);
+	}
+
+	dtrace: description 'kinst::cam_iosched_has_more_trim:entry ' matched 4 probes
+	CPU     ID                    FUNCTION:NAME
+	  0  81502          cam_iosched_schedule:40     2       clock
+	  0  81501          cam_iosched_next_bio:13     2       clock
+	  2  81502          cam_iosched_schedule:40     2       clock
+	  1  81502          cam_iosched_next_bio:13     0	kernel
+	  1  81503          cam_iosched_schedule:40     0	kernel
+	^C
+....
+
+A new `-d` flag has also been added to man:dtrace[1] which dumps the D script after libdtrace has applied syntactic transformations.
+
+Further goals include:
+
+* Implement a `locals` structure in D which stores the local variables of the traced function.
+  For example with `kinst::foo:<x>`, we could print the local variable `bar` by doing `print(locals->bar)` inside a D script.
+* Port kinst to riscv and/or arm64.
+
+Sponsor: The FreeBSD Foundation