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From: "wcohen at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: systemtap@sourceware.org
Subject: [Bug bpf/24804] New: bpf code generation unable to determine type of target variable used to index global variable
Date: Thu, 11 Jul 2019 17:43:00 -0000
X-Bugzilla-Reason: AssignedTo
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-Who: wcohen at redhat dot com
X-Bugzilla-Status: NEW
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D24804

            Bug ID: 24804
           Summary: bpf code generation unable to determine type of target
                    variable used to index global variable
           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: ---

When experimenting with the bpf tracepoints on the most currently checked o=
ut
version of systemtap came across the following problem where the target
variable seems to be properly typed, but when used as an index for a global
array systemtap reports it can't determine the type:

[wcohen@localhost systemtap]$ rpm -q systemtap
systemtap-4.2-1.201907111323.fc31.x86_64
[wcohen@localhost systemtap]$ stap  --bpf -L 'kernel.trace("sys_enter")'=20
kernel.trace("raw_syscalls:sys_enter") $id:long int $args:long unsigned int=
[]
[wcohen@localhost systemtap]$ stap --bpf -e 'global ids; probe
kernel.trace("sys_enter"){ids[$id]++}' -T 10
semantic error: unresolved type : identifier '$id' at <input>:1:49
        source: global ids; probe kernel.trace("sys_enter"){ids[$id]++}
                                                                ^

Pass 2: analysis failed.  [man error::pass2]
Number of similar error messages suppressed: 1.
Rerun with -v to see them.

However, it looks for some cases systemtap can determine the target variable
type as the following works:

[wcohen@localhost systemtap]$ stap  -m good -e 'probe
kernel.trace("sys_enter"){printf("syscall %d\n", $id); exit()}'
syscall 72


The traditional linux kernel module version works fine:

[wcohen@localhost systemtap]$ stap   -L 'kernel.trace("sys_enter")'=20
kernel.trace("raw_syscalls:sys_enter") $regs:struct pt_regs* $id:long int
[wcohen@localhost systemtap]$ stap  -e 'global ids; probe
kernel.trace("sys_enter"){ids[$id]++}' -T 10
ids[39]=3D719
ids[72]=3D595
ids[0]=3D577
ids[5]=3D332
ids[3]=3D307
ids[257]=3D208
ids[228]=3D172
ids[7]=3D115
ids[213]=3D106
...

--=20
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