[Bug translator/23866] dissonance between kernel tracepoint parametrization, lkm vs bpf

["wcohen at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=23866

William Cohen <wcohen at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #11866|0                           |1
        is obsolete|                            |
  Attachment #11901|0                           |1
        is obsolete|                            |

--- Comment #7 from William Cohen <wcohen at redhat dot com> ---
Created attachment 11907
  --> https://sourceware.org/bugzilla/attachment.cgi?id=11907&action=edit
Revised version of the WIP bpf raw tracepoint support

The patch still needs some work:

-modify stapbpf/stapbpf.cxx to allow it to compile on machines that don't have
raw tracepoint support (for example rhel7).
-have clearer handling of things if using the older non-raw bpf tracepoints
-correct access of target struct field arguments (this issue can be seen in the
example below)
-cache tracequery results to speed up the process

$  ../install/bin/stap --bpf -e 'probe kernel.trace("sched_switch"){printf("%d
%p(%d) %p(%d)\n", $preempt, $prev, $prev->pid, $next, $next->pid)}' -T 0.01
0 0xffff8d78706b0000(7260) 0xffff8d78706b3380(7260)
0 0xffff8d78706b3380(29440) 0xffff8d78ba488000(29440)
0 0xffff8d78ba488000(11) 0xffff8d78bcd30000(11)
0 0xffff8d78bcd30000(7260) 0xffff8d78706b3380(7260)
1 0xffff8d78706b3380(1499) 0xffff8d7857d4b380(1499)
0 0xffff8d7857d4b380(6714) 0xffff8d7880628000(6714)
0 0xffff8d7880628000(748) 0xffff8d78ba48b380(748)
0 0xffff8d78ba48b380(29440) 0xffff8d78ba488000(29440)
0 0xffff8d78ba488000(489) 0xffff8d7876410000(489)
0 0xffff8d7876410000(7260) 0xffff8d78706b3380(7260)
0 0xffff8d78706b3380(1499) 0xffff8d7857d4b380(1499)
...

comparing to lkm version which has 0xffff8d78bcd30000(11) looks like getting
the fields for $prev wrong
$  ../install/bin/stap -e 'probe kernel.trace("sched_switch"){printf("%d %p(%d)
%p(%d)\n", $preempt, $prev, $prev->pid, $next, $next->pid)}' -T 0.01
0 0xffff8d78706b0000(11032) 0xffff8d787fb83380(11035)
0 0xffff8d787fb83380(11035) 0xffff8d78bc6b8000(137)
1 0xffff8d78bc6b8000(137) 0xffff8d78ba488000(29440)
0 0xffff8d78ba488000(29440) 0xffff8d78bc6b8000(137)
1 0xffff8d78bc6b8000(137) 0xffff8d78bcd30000(11)
0 0xffff8d78bcd30000(11) 0xffff8d78bc6b8000(137)
1 0xffff8d78bc6b8000(137) 0xffff8d78bcd30000(11)
0 0xffff8d78bcd30000(11) 0xffff8d78bc6b8000(137)
1 0xffff8d78bc6b8000(137) 0xffff8d78bcd30000(11)
0 0xffff8d78bcd30000(11) 0xffff8d78bc6b8000(137)
1 0xffff8d78bc6b8000(137) 0xffff8d7857d48000(10951)
0 0xffff8d7857d48000(10951) 0xffff8d78bc6b8000(137)
1 0xffff8d78bc6b8000(137) 0xffff8d7857d48000(10951)
0 0xffff8d7857d48000(10951) 0xffff8d78bc6b8000(137)

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