* [Bug bpf/24639] "next" statement not recognized by stap bpf backend
2019-06-05 15:29 [Bug bpf/24639] New: "next" statement not recognized by stap bpf backend wcohen at redhat dot com
@ 2019-06-05 20:34 ` me at serhei dot io
2019-06-06 21:13 ` wcohen at redhat dot com
` (5 subsequent siblings)
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From: me at serhei dot io @ 2019-06-05 20:34 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=24639
Serhei Makarov <me at serhei dot io> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |me at serhei dot io
--- Comment #1 from Serhei Makarov <me at serhei dot io> ---
Implementing next statement for probes should not be difficult. The other
behaviour is for overloaded functions, which are currently not supported by the
bpf backend.
Pushed a rudimentary implementation in patch
https://sourceware.org/git/gitweb.cgi?p=systemtap.git;a=commitdiff;h=d7679e5526832d70f435a58004a211d35818bf36
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* [Bug bpf/24639] "next" statement not recognized by stap bpf backend
2019-06-05 15:29 [Bug bpf/24639] New: "next" statement not recognized by stap bpf backend wcohen at redhat dot com
2019-06-05 20:34 ` [Bug bpf/24639] " me at serhei dot io
@ 2019-06-06 21:13 ` wcohen at redhat dot com
2019-06-06 21:30 ` wcohen at redhat dot com
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: wcohen at redhat dot com @ 2019-06-06 21:13 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=24639
--- Comment #2 from William Cohen <wcohen at redhat dot com> ---
The bpf back is recognizing the next statement in probes, but the tests fail:
$ ../install/bin/stap --bpf testsuite/systemtap.bpf/bpf_tests/next.stp
BEGIN
END FAIL
Looks like there is a problem with if statements code generation:
$ ../install/bin/stap --bpf -e 'global a, b; probe init {a=10; b=10} probe
oneshot{if (a!=b) printf("!=\n") else printf("==\n")}'
==
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* [Bug bpf/24639] "next" statement not recognized by stap bpf backend
2019-06-05 15:29 [Bug bpf/24639] New: "next" statement not recognized by stap bpf backend wcohen at redhat dot com
2019-06-05 20:34 ` [Bug bpf/24639] " me at serhei dot io
2019-06-06 21:13 ` wcohen at redhat dot com
@ 2019-06-06 21:30 ` wcohen at redhat dot com
2019-06-06 21:30 ` wcohen at redhat dot com
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: wcohen at redhat dot com @ 2019-06-06 21:30 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=24639
--- Comment #3 from William Cohen <wcohen at redhat dot com> ---
Created attachment 11817
--> https://sourceware.org/bugzilla/attachment.cgi?id=11817&action=edit
next.stp with diagnostic prints.
ignore the previous -e example. that isn't reproducing the problem.
It looks like changes in the values made by the kernel.function("vfs_read")
probes are not seen in the probe end. Put in the diagnostic printf in the
probes to better see what is going on.
[wcohen@localhost systemtap]$ ../install/bin/stap --bpf next.stp
BEGIN
vfs_read
value 2
status 0
end
value 2
status 2
END FAIL
[wcohen@localhost systemtap]$ ../install/bin/stap --bpf next.stp
BEGIN
vfs_read
value 0
status 0
end
value 2
status 2
END FAIL
--- Comment #4 from William Cohen <wcohen at redhat dot com> ---
Created attachment 11818
--> https://sourceware.org/bugzilla/attachment.cgi?id=11818&action=edit
next.stp with diagnostic prints.
ignore the previous -e example. that isn't reproducing the problem.
It looks like changes in the values made by the kernel.function("vfs_read")
probes are not seen in the probe end. Put in the diagnostic printf in the
probes to better see what is going on.
[wcohen@localhost systemtap]$ ../install/bin/stap --bpf next.stp
BEGIN
vfs_read
value 2
status 0
end
value 2
status 2
END FAIL
[wcohen@localhost systemtap]$ ../install/bin/stap --bpf next.stp
BEGIN
vfs_read
value 0
status 0
end
value 2
status 2
END FAIL
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* [Bug bpf/24639] "next" statement not recognized by stap bpf backend
2019-06-05 15:29 [Bug bpf/24639] New: "next" statement not recognized by stap bpf backend wcohen at redhat dot com
` (2 preceding siblings ...)
2019-06-06 21:30 ` wcohen at redhat dot com
@ 2019-06-06 21:30 ` wcohen at redhat dot com
2019-06-06 21:37 ` me at serhei dot io
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: wcohen at redhat dot com @ 2019-06-06 21:30 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=24639
--- Comment #3 from William Cohen <wcohen at redhat dot com> ---
Created attachment 11817
--> https://sourceware.org/bugzilla/attachment.cgi?id=11817&action=edit
next.stp with diagnostic prints.
ignore the previous -e example. that isn't reproducing the problem.
It looks like changes in the values made by the kernel.function("vfs_read")
probes are not seen in the probe end. Put in the diagnostic printf in the
probes to better see what is going on.
[wcohen@localhost systemtap]$ ../install/bin/stap --bpf next.stp
BEGIN
vfs_read
value 2
status 0
end
value 2
status 2
END FAIL
[wcohen@localhost systemtap]$ ../install/bin/stap --bpf next.stp
BEGIN
vfs_read
value 0
status 0
end
value 2
status 2
END FAIL
--- Comment #4 from William Cohen <wcohen at redhat dot com> ---
Created attachment 11818
--> https://sourceware.org/bugzilla/attachment.cgi?id=11818&action=edit
next.stp with diagnostic prints.
ignore the previous -e example. that isn't reproducing the problem.
It looks like changes in the values made by the kernel.function("vfs_read")
probes are not seen in the probe end. Put in the diagnostic printf in the
probes to better see what is going on.
[wcohen@localhost systemtap]$ ../install/bin/stap --bpf next.stp
BEGIN
vfs_read
value 2
status 0
end
value 2
status 2
END FAIL
[wcohen@localhost systemtap]$ ../install/bin/stap --bpf next.stp
BEGIN
vfs_read
value 0
status 0
end
value 2
status 2
END FAIL
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* [Bug bpf/24639] "next" statement not recognized by stap bpf backend
2019-06-05 15:29 [Bug bpf/24639] New: "next" statement not recognized by stap bpf backend wcohen at redhat dot com
` (3 preceding siblings ...)
2019-06-06 21:30 ` wcohen at redhat dot com
@ 2019-06-06 21:37 ` me at serhei dot io
2019-06-07 13:49 ` wcohen at redhat dot com
2019-06-10 17:11 ` me at serhei dot io
6 siblings, 0 replies; 8+ messages in thread
From: me at serhei dot io @ 2019-06-06 21:37 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=24639
--- Comment #5 from Serhei Makarov <me at serhei dot io> ---
Weird, since it passes consistently on earlier 4.18.0 kernel. To me that trace
looks like something went wrong writing to the global variable map.
Which kernel version are you using on Fedora 30?
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* [Bug bpf/24639] "next" statement not recognized by stap bpf backend
2019-06-05 15:29 [Bug bpf/24639] New: "next" statement not recognized by stap bpf backend wcohen at redhat dot com
` (4 preceding siblings ...)
2019-06-06 21:37 ` me at serhei dot io
@ 2019-06-07 13:49 ` wcohen at redhat dot com
2019-06-10 17:11 ` me at serhei dot io
6 siblings, 0 replies; 8+ messages in thread
From: wcohen at redhat dot com @ 2019-06-07 13:49 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=24639
--- Comment #6 from William Cohen <wcohen at redhat dot com> ---
Due to the crashes with bpf on f30 fedora 5.1.x kernels. This was on a rawhide
machine:
$ uname -a
Linux localhost.localdomain 5.2.0-0.rc3.git0.1.fc31.x86_64 #1 SMP Mon Jun 3
13:27:29 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
However, got same failure on f29:
$ uname -a
Linux fedora29 5.0.19-200.fc29.x86_64 #1 SMP Tue May 28 13:56:29 UTC 2019
x86_64 x86_64 x86_64 GNU/Linux
$ sudo ../install/bin/stap --bpf next.stp
BEGIN
vfs_read
value 2
status 0
end
value 2
status 2
END FAIL
Maybe there is some change in the kernel that is allowing for incoherent values
between kernel and user space.
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* [Bug bpf/24639] "next" statement not recognized by stap bpf backend
2019-06-05 15:29 [Bug bpf/24639] New: "next" statement not recognized by stap bpf backend wcohen at redhat dot com
` (5 preceding siblings ...)
2019-06-07 13:49 ` wcohen at redhat dot com
@ 2019-06-10 17:11 ` me at serhei dot io
6 siblings, 0 replies; 8+ messages in thread
From: me at serhei dot io @ 2019-06-10 17:11 UTC (permalink / raw)
To: systemtap
https://sourceware.org/bugzilla/show_bug.cgi?id=24639
Serhei Makarov <me at serhei dot io> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |FIXED
--- Comment #7 from Serhei Makarov <me at serhei dot io> ---
It appears that the recent kernels introduces some timing issue between kernel-
and user-space map operations. Filing as stapbpf pr24659
Changing the second probe vfs_read to probe timer.s(2) would make the testcase
pass on new kernels as well as old ones. But let's keep next.stp as-is and use
it to test for pr24659 as well.
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