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From: "wcohen at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: systemtap@sourceware.org
Subject: [Bug bpf/24656] New: Target variables for tracepoints differ between traditional sytemtap backend and bpf backend
Date: Mon, 10 Jun 2019 14:35:00 -0000
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X-Bugzilla-Type: new
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X-Bugzilla-Product: systemtap
X-Bugzilla-Component: bpf
X-Bugzilla-Version: unspecified
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: wcohen at redhat dot com
X-Bugzilla-Status: NEW
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X-Bugzilla-Priority: P2
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D24656

            Bug ID: 24656
           Summary: Target variables for tracepoints differ between
                    traditional sytemtap backend and bpf backend
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: bpf
          Assignee: systemtap at sourceware dot org
          Reporter: wcohen at redhat dot com
  Target Milestone: ---

After getting the target() function working I expected that the cycle_thief=
.stp
example would work with the bpf backend.  However, found that the bpf backe=
nd
has a different set of target variables available than the original systemt=
ap
kernel module backend:

[wcohen@localhost systemtap]$ ../install/bin/stap -L
'kernel.trace("sched_switch")'
kernel.trace("sched:sched_switch") $preempt:bool $prev:struct task_struct*
$next:struct task_struct*
[wcohen@localhost systemtap]$ ../install/bin/stap --bpf -L
'kernel.trace("sched_switch")'
kernel.trace("sched:sched_switch") $prev_comm:char[] $prev_pid:pid_t
$prev_prio:int $prev_state:long int $next_comm:char[] $next_pid:pid_t
$next_prio:int

Did not see this type of difference between probes for a kernel function. F=
or
example the vfs_read probes are the same:

[wcohen@localhost systemtap]$ ../install/bin/stap -L
'kernel.function("vfs_read")'=20
kernel.function("vfs_read@fs/read_write.c:446") $file:struct file* $buf:cha=
r*
$count:size_t $pos:loff_t*
[wcohen@localhost systemtap]$ ../install/bin/stap --bpf -L
'kernel.function("vfs_read")'=20
kernel.function("vfs_read@fs/read_write.c:446") $file:struct file* $buf:cha=
r*
$count:size_t $pos:loff_t*

--=20
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