fche at redhat dot com | 29 Aug 00:24 2015

[Bug runtime/18889] New: lost ability to probe kernel module initializers

https://sourceware.org/bugzilla/show_bug.cgi?id=18889

            Bug ID: 18889
           Summary: lost ability to probe kernel module initializers
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: fche at redhat dot com
  Target Milestone: ---

On recent kernels, a probe requested on module .init.* functions no longer
receives hits.  This appears to be because the kernel MODULE_STATE_COMING
notification is coming too early (before the module_sect_attrs are set), so we
cannot relocate symbols against .init.*, and thus cannot place probes.  The
bz6503.* test case was too permissive to let us discover this immediately.  The
kernel change that broke stap has not yet been identified.

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jistone at redhat dot com | 28 Aug 21:04 2015

[Bug tapsets/18885] New: Use /* unmodified-fnargs */ in tapsets

https://sourceware.org/bugzilla/show_bug.cgi?id=18885

            Bug ID: 18885
           Summary: Use /* unmodified-fnargs */ in tapsets
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: tapsets
          Assignee: systemtap at sourceware dot org
          Reporter: jistone at redhat dot com
  Target Milestone: ---

PR11528 added a nice string optimization, and the /* unmodified-fnargs */
pragma for embedded-C functions to opt into this.  But we're not using this
anywhere in our own tapsets, and there are plenty of opportunities, e.g. all of
logging.stp.

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jistone at redhat dot com | 28 Aug 20:57 2015

[Bug translator/18884] New: const-folded literals get unnecessary tmp storage

https://sourceware.org/bugzilla/show_bug.cgi?id=18884

            Bug ID: 18884
           Summary: const-folded literals get unnecessary tmp storage
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: minor
          Priority: P2
         Component: translator
          Assignee: systemtap at sourceware dot org
          Reporter: jistone at redhat dot com
  Target Milestone: ---

Thanks to the const-folding pass, trivial numeric and string operations are
reduced in pass-2.  You can see this in -vp2 of the following probes:

  probe oneshot { println("foobar") }
  probe oneshot { println("foo" . "bar") }

The second one becomes just like the first, as println("foobar").

In the translator pass, we also try to avoid tmp copies of literal values, and
instead just emit the values directly into their expressions.  However, this is
compared on the tok->type rather than checking if the expression itself is a
literal.  The pattern in translate.cxx looks like this:

  if (val->tok->type == tok_number || val->tok->type == tok_string)
    tmpval.override(c_expression(val))

(Continue reading)

fche at redhat dot com | 26 Aug 22:28 2015

[Bug tapsets/18876] New: need to assert

https://sourceware.org/bugzilla/show_bug.cgi?id=18876

            Bug ID: 18876
           Summary: need to assert
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tapsets
          Assignee: systemtap at sourceware dot org
          Reporter: fche at redhat dot com
  Target Milestone: ---

We have several bits of code in the tapset (and perhaps also in the
samples) looking like this:

   if (condition) {
      error("foo")
      return 0
   }

(Note first that any statements after an error() call are already
dead.)

Let's have a new tapset function like assert(), so all that type of
code can look like this instead:

   assert(condition, "foo")

(Continue reading)

flu at redhat dot com | 26 Aug 19:33 2015

[Bug translator/10977] Getting the address size used in a module

https://sourceware.org/bugzilla/show_bug.cgi?id=10977

Felix Lu <flu at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |flu at redhat dot com
         Resolution|---                         |FIXED

--- Comment #5 from Felix Lu <flu at redhat dot com> ---
added functions arch_bytes() and uarch_bytes in commit
93f70a9a97a8fe4a13c59c57155d75b534d02e3e.

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flu at redhat dot com | 25 Aug 21:49 2015

[Bug documentation/16968] bad formatting in many help pages for probes

https://sourceware.org/bugzilla/show_bug.cgi?id=16968

Felix Lu <flu at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |flu at redhat dot com
         Resolution|---                         |FIXED

--- Comment #3 from Felix Lu <flu at redhat dot com> ---
Fixed in commit 7441e8ec677e50f60acf90576fd190837d412ea6

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flu at redhat dot com | 24 Aug 17:48 2015

[Bug tapsets/10487] flight recorder control from script

https://sourceware.org/bugzilla/show_bug.cgi?id=10487

Felix Lu <flu at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |flu at redhat dot com
         Resolution|---                         |FIXED

--- Comment #4 from Felix Lu <flu at redhat dot com> ---
A new tapset function switch_file() provides this functionality.

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Daniel Heller | 24 Aug 14:07 2015
Picon

User Memory Read Failure Question

Hello,

I've built a userland tracing mechanism on top of SystemTap which I
and my colleagues have used fruitfully for quite a while.  Recently, I
got a report that some of my users on linux 3.18.16/x64/SystemTap 2.7
were seeing missing data in some of my probe logging; on the systems
in question, I can reliably reproduce the problem, but on other
similarly configured systems, I cannot reproduce it at all.  I have
found that reads for certain user addresses are reliably failing even
though examinations of /proc/${pid}/maps show that the regions are
mapped with read access; reads of the same addresses through
/proc/${pid}/mem and examination of core files both find the expected
values at the locations in question (SystemTap continues to fail to
read after that manual examination, so I do not believe that my manual
reads changed the state which is causing the problem).  Since I am
tracing an interpreter (Node.js 0.10) whose behavior I don't fully
understand, it's possible that the process itself is changing
permissions on the pages dynamically, causing the reads to fail.  I
haven't been able to disprove this possibility.  As I've been trying
to investigate, I've begun to wonder:

(a) Whether Linux may be unmapping the pages (but leaving them
resident) for access detection, and whether if that happened,
SystemTap would fail user reads to avoid potential recursive faulting
behavior.

(b) Whether there may be reasons for systemtap read failures other
than invalid mappings that I haven't anticipated but would be able to
check for.

(Continue reading)

dsmith at redhat dot com | 20 Aug 17:00 2015

[Bug tapsets/18856] New: nfsd.close probe alias fails on rawhide

https://sourceware.org/bugzilla/show_bug.cgi?id=18856

            Bug ID: 18856
           Summary: nfsd.close probe alias fails on rawhide
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tapsets
          Assignee: systemtap at sourceware dot org
          Reporter: dsmith at redhat dot com
  Target Milestone: ---

On rawhide (4.2.0-0.rc6.git1.1.fc24.x86_64), the nfsd.close probe alias no
longer resolves:

====
# stap -p4 -e 'probe nfsd.close {}'
semantic error: while resolving probe point: identifier 'nfsd' at <input>:1:7
        source: probe nfsd.close {}
                      ^

semantic error: no match

Pass 2: analysis failed.  [man error::pass2]
====

This is because of the following kernel commit:

(Continue reading)

Abe Jakop | 18 Aug 22:35 2015
Picon

SystemTap's reduced memory usage

Hello everyone,

Work has been done to reduce the amount of memory SystemTap consumes.

A need for this optimization was brought up by the case where there is a
large amount of outside tapsets, such that stap's excessive memory
usage shows.

To optimize SystemTap's memory usage, struct interned_string was introduced
as a wrapper on Boost's string_ref. These interned_strings are meant to
replace a handful of instances of std::strings. 

The new interned_strings are meant to act like pointers to existing
strings. With this change, instances where new duplicate strings were
created are now replaced with a sort of pointer to the original string's
location, reducing the number of new strings that are generated.

These changes are already merged into the master branch. To try out the
changes, see the master branch of the git repo:

https://sourceware.org/git/gitweb.cgi?p=systemtap.git

Notable changes would be the inclusion of files stringtable.h and
stringtable.cxx, and the new peculiarities sections in INTERNALS.

____
NOTE

This optimization is reliant on having Boost version >=1.53, such that
boost::string_ref is available. To see if boost string_ref is available
(Continue reading)

fche at redhat dot com | 18 Aug 21:23 2015

[Bug runtime/18851] New: new --interactive mode

https://sourceware.org/bugzilla/show_bug.cgi?id=18851

            Bug ID: 18851
           Summary: new --interactive mode
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: fche at redhat dot com
                CC: dsmith at redhat dot com
  Target Milestone: ---

We'd like to have a systemtap mode that is more similar to an interactive
debugger.  Here, the stap script is not solely supplied from a file, but
incrementally & interactively built by the user.  stap would present a command
line to add / delete / monitor stap probes/functions/etc. as they are being
executed.

See also bug #18848.

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Gmane