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[Bug translator/13842] New: aggressive cast accessor function merging gives confusing error messages
- From: "mjw at redhat dot com" <sourceware-bugzilla at sourceware dot org>
- To: systemtap at sourceware dot org
- Date: Tue, 13 Mar 2012 22:37:30 +0000
- Subject: [Bug translator/13842] New: aggressive cast accessor function merging gives confusing error messages
- Auto-submitted: auto-generated
http://sourceware.org/bugzilla/show_bug.cgi?id=13842
Bug #: 13842
Summary: aggressive cast accessor function merging gives
confusing error messages
Product: systemtap
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: translator
AssignedTo: systemtap@sourceware.org
ReportedBy: mjw@redhat.com
Classification: Unclassified
There are two (bad) @casts in the following script:
$ stap -e 'global v=0; probe process("/bin/ls").function("main") { if (v == 1)
{ v = @cast(v, "timespec")->tv_sec } else { v = @cast(v + 1,
"timespec")->tv_sec } }' -c '/bin/ls /dev/zero'
/dev/zero
ERROR: kernel read fault at 0x0000000000000001 (addr) near identifier '@cast'
at <input>:1:75
WARNING: Number of errors: 1, skipped probes: 0
WARNING: /usr/bin/staprun exited with status: 1
Pass 5: run failed. Try again with another '--vp 00001' option.
Note that the error message points to the wrong @cast (the first, while the
second triggered the bad read).
When using -u the error message is correct:
$ stap -u -e 'global v=0; probe process("/bin/ls").function("main") { if (v ==
1) { v = @cast(v, "timespec")->tv_sec } else { v = @cast(v + 1,
"timespec")->tv_sec } }' -c '/bin/ls /dev/zero'
/dev/zero
ERROR: kernel read fault at 0x0000000000000001 (addr) near identifier '@cast'
at <input>:1:117
WARNING: Number of errors: 1, skipped probes: 0
WARNING: /usr/bin/staprun exited with status: 1
Pass 5: run failed. Try again with another '--vp 00001' option.
Also note that this can also happen with different structures where the field
accessed is at the same offset in each.
Things especially get confusing if one of these @casts is wrapped in a try {
... } catch { ... }. Then the user might get an error about a location (inside
the try_block) where no such error can occur.
Three small other observations about this error message:
- It isn't a "kernel read" really, but a "user space read".
- Why does the error message say (addr)?
- If you switch the v == 1 to v == 0 (or remove the + 1 from v + 1) the error
message becomes "read fault at 0x (null) (addr)". weird...
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