path: root/NEWS

* What's new

- A serious problem associated with user-space probing in shared libraries
  was corrected, making it now possible to experiment with probe shared
  libraries.  Assuming dwarf debugging information is installed, use this
  twist on the normal syntax:

    probe process("/lib64/libc-2.8.so").function("....") { ... }

  This would probe all threads that call into that library.  Running
  "stap -c CMD" or "stap -x PID" naturally restricts this to the target
  command+descendants only.

- For scripts that sometimes terminate with excessive "skipped" probes,
  rerunning the script with "-t" (timing) will print more details about
  the skippage reasons.

- Symbol tables and unwind (backtracing) data support were formerly
  compiled in for all probed modules as identified by the script
  (kernel; module("name"); process("file")) plus those listed by the
  stap "-d BINARY" option.  Now, this data is included only if the systemtap
  script uses tapset functions like probefunc() or backtrace() that require
  such information.  This shrinks the probe modules considerably for the rest.

- Per-pass verbosity control is available with the new "--vp {N}+" option.
  "stap --vp 040" adds 4 units of -v verbosity only to pass 2.  This is useful
  for diagnosing errors from one pass without excessive verbosity from others.

- Most probe handlers now run with interrupts enabled, for improved
  system responsiveness and less probing overhead.  This may result
  in more skipped probes, for example if a reentrant probe handler
  is attempted from within an interrupt handler.  It may also make the
  systemtap overload detection facility more likely to be triggered, as
  interrupt handlers' run time would be included in the self-assessed
  overhead of running probe handlers.

* What's new in version 0.8

- Cache limiting is now available.  If the compiled module cache size is
  over a limit specified in the $SYSTEMTAP_DIR/cache/cache_mb_limit file,
  some old cache entries will be unlinked.  See man stap(1) for more.

- Error and warning messages are now followed by source context displaying
  the erroneous line/s and a handy '^' in the following line pointing to the
  appropriate column.

- A bug reporting tool "stap-report" is now available which will quickly
  retrieve much of the information requested here: 
  http://sourceware.org/systemtap/wiki/HowToReportBugs

- The translator can resolve members of anonymous structs / unions:
    given            struct { int foo; struct { int bar; }; } *p;
    this now works:  $p->bar

- The stap "-F" flag activates "flight recorder" mode, which consists of
  translating the given script as usual, but implicitly launching it into
  the background with staprun's existing "-L" (launch) option.  A user
  can later reattach to the module with "staprun -A MODULENAME".

- Additional context variables are available on user-space syscall probes.
  - $argN ($arg1, $arg2, ... $arg6) in process(PATH_OR_PID).syscall
    gives you the argument of the system call.
  - $return in process(PATH_OR_PID).syscall.return gives you the return
    value of the system call.

- Target process mode (stap -c CMD or -x PID) now implicitly restricts all
  "process.*" probes to the given child process.  (It does not affect
  kernel.* or other probe types.)  The CMD string is normally run directly,
  rather than via a /bin/sh -c subshell, since then utrace/uprobe probes
  receive a fairly "clean" event stream.  If metacharacters like
  redirection operators were present in CMD, then "sh -c CMD" is still
  used, and utrace/uprobe probes will receive events from the shell.

     % stap -e 'probe process.syscall, process.end {
                   printf("%s %d %s\n", execname(), pid(), pp())}'\
            -c ls
     ls 2323 process.syscall 
     ls 2323 process.syscall 
     ls 2323 process.end

- Probe listing mode is improved: "-L" lists available script-level variables

     % stap -L 'syscall.*open*'
     syscall.mq_open name:string name_uaddr:long filename:string mode:long u_attr_uaddr:long oflag:long argstr:string
     syscall.open name:string filename:string flags:long mode:long argstr:string
     syscall.openat name:string filename:string flags:long mode:long argstr:string

- All user-space-related probes support $PATH-resolved executable
  names, so

     probe process("ls").syscall {}
     probe process("./a.out").syscall {}

  work now, instead of just

     probe process("/bin/ls").syscall {}
     probe process("/my/directory/a.out").syscall {}

- Prototype symbolic user-space probing support:

     # stap -e 'probe process("ls").function("*").call {
                   log (probefunc()." ".$$parms)
                }' \
            -c 'ls -l'

  This requires:
  - debugging information for the named program
  - a version of utrace in the kernel that is compatible with the "uprobes"
    kernel module prototype.  This includes RHEL5 and older Fedora, but not
    yet current lkml-track utrace; a "pass 4a"-time build failure means
    your system cannot use this yet.

- Prototype systemtap client and compile server are now available.
  These allow you to compile a systemtap module on a host other than
  the one which it will be run, providing the client and server
  are compatible. Other than using a server for passes 1 through
  4, the client behaves like the 'stap' front end itself. This
  means, among other things, that the client will automatically
  load the resulting module on the local host unless -p[1234]
  was specified.

  This client/server implementation is a prototype. It provides
  NO NETWORK SECURITY OF ANY KIND and should be used only
  among trusted hosts on a trusted network.

  See stap-server(8) for more details.

- Global variables which are written to but never read are now
  automatically displayed when the session does a shutdown.  For example:

      global running_tasks
      probe timer.profile {running_tasks[pid(),tid()] = execname()}
      probe timer.ms(8000) {exit()}

- A formatted string representation of the variables, parameters, or local
  variables at a probe point is now supported via the special $$vars,
  $$parms, and $$locals context variables, which expand to a string
  containing a list "var1=0xdead var2=0xbeef var3=?".  (Here, var3 exists
  but is for some reason unavailable.)  In return probes only, $$return
  expands to an empty string for a void function, or "return=0xf00".


* What's new in version 0.7

- .statement("func@file:*") and .statement("func@file:M-N") probes are now
  supported to allow matching a range of lines in a function.  This allows
  tracing the execution of a function.

- Scripts relying on probe point wildcards like "syscall.*" that expand
  to distinct kprobes are processed significantly faster than before.

- The vector of script command line arguments is available in a
  tapset-provided global array argv[].  It is indexed 1 ... argc,
  another global.  This can substitute for of preprocessor
  directives @NNN that fail at parse time if there are not
  enough arguments.

      printf("argv: %s %s %s", argv[1], argv[2], argv[3])

- .statement("func@file+line") probes are now supported to allow a
  match relative to the entry of the function incremented by line
  number.  This allows using the same systemtap script if the rest
  of the file.c source only changes slightly.

- A probe listing mode is available.
  % stap -l vm.*
  vm.brk
  vm.mmap
  vm.munmap
  vm.oom_kill
  vm.pagefault
  vm.write_shared

- More user-space probe types are added:

  probe process(PID).begin { }
  probe process("PATH").begin { }
  probe process(PID).thread.begin { }
  probe process("PATH").thread.begin { }
  probe process(PID).end { }
  probe process("PATH").end { }
  probe process(PID).thread.end { }
  probe process("PATH").thread.end { }
  probe process(PID).syscall { }
  probe process("PATH").syscall { }
  probe process(PID).syscall.return { }
  probe process("PATH").syscall.return { }

- Globals now accept ; terminators

  global odds, evens;
  global little[10], big[5];

* What's new in version 0.6

- A copy of the systemtap tutorial and language reference guide
  are now included.

- There is a new format specifier, %m, for the printf family of
  functions.  It functions like %s, except that it does not stop when
  a nul ('\0') byte is encountered.  The number of bytes output is
  determined by the precision specifier.  The default precision is 1.
  For example:

      printf ("%m", "My String") // prints one character: M
      printf ("%.5", myString)   // prints 5 bytes beginning at the start
      	     	     		 // of myString

- The %b format specifier for the printf family of functions has been enhanced
  as follows:

  1) When the width and precision are both unspecified, the default is %8.8b.
  2) When only one of the width or precision is specified, the other defaults
     to the same value.  For example, %4b == %.4b == %4.4b
  3) Nul ('\0') bytes are used for field width padding.  For example,

     printf ("%b", 0x1111deadbeef2222) // prints all eight bytes
     printf ("%4.2b", 0xdeadbeef)      // prints  \0\0\xbe\xef

- Dynamic width and precision are now supported for all printf family format
  specifiers.  For example:

     four = 4
     two = 2
     printf ("%*.*b", four, two, 0xdeadbbeef) // prints  \0\0\xbe\xef
     printf ("%*d", four, two)                // prints  <space><space><space>2

- Preprocessor conditional expressions can now include wildcard style
  matches on kernel versions.
  %( kernel_vr != "*xen" %? foo %: bar %)

- Prototype support for user-space probing is showing some progress.
  No symbolic notations are supported yet (so no probing by function names,
  file names, process names, and no access to $context variables), but at
  least it's something:

    probe process(PID).statement(ADDRESS).absolute { }

  This will set a uprobe on the given process-id and given virtual address.
  The proble handler runs in kernel-space as usual, and can generally use
  existing tapset functions.

- Crash utility can retrieve systemtap's relay buffer from a kernel dump
  image by using staplog which is a crash extension module. To use this
  feature, type commands as below from crash(8)'s command line:

    crash> extend staplog.so
    crash> help systemtaplog

  Then, you can see more precise help message.

- You can share a relay buffer amoung several scripts and merge outputs from
  several scripts by using "-DRELAY_HOST" and "-DRELAY_GUEST" options.
  For example:

    # run a host script
    % stap -ve 'probe begin{}' -o merged.out -DRELAY_HOST &
    # wait until starting the host.
    % stap -ve 'probe begin{print("hello ");exit()}' -DRELAY_GUEST
    % stap -ve 'probe begin{print("world\n");exit()}' -DRELAY_GUEST

  Then, you'll see "hello world" in merged.out.

- You can add a conditional statement for each probe point or aliase, which
  is evaluated when the probe point is hit. If the condition is false, the
  whole probe body(including aliases) is skipped. For example:

    global switch = 0;
    probe syscall.* if (switch) { ... }
    probe procfs.write {switch = strtol($value,10)} /* enable/disable ctrl */

- Systemtap will warn you if your script contains unused variables or
  functions.  This is helpful in case of misspelled variables.  If it
  doth protest too much, turn it off with "stap -w ...".

- You can add error-handling probes to a script, which are run if a
  script was stopped due to errors.  In such a case, "end" probes are
  not run, but "error" ones are.

    probe error { println ("oops, errors encountered; here's a report anyway")
                  foreach (coin in mint) { println (coin) } }

- In a related twist, one may list probe points in order of preference,
  and mark any of them as "sufficient" beyond just "optional".  Probe
  point sequence expansion stops if a sufficient-marked probe point has a hit.
  This is useful for probes on functions that may be in a module (CONFIG_FOO=m)
  or may have been compiled into the kernel (CONFIG_FOO=y), but we don't know
  which.  Instead of

    probe module("sd").function("sd_init_command") ? ,
          kernel.function("sd_init_command") ? { ... }

  which might match neither, now one can write this:

    probe module("sd").function("sd_init_command") ! , /* <-- note excl. mark */
          kernel.function("sd_init_command")  { ... }

- New security model.  To install a systemtap kernel module, a user
  must be one of the following: the root user; a member of the
  'stapdev' group; or a member of the 'stapusr' group.  Members of the
  stapusr group can only use modules located in the
  /lib/modules/VERSION/systemtap directory (where VERSION is the
  output of "uname -r").

- .statement("...@file:line") probes now apply heuristics to allow an
  approximate match for the line number.  This works similarly to gdb,
  where a breakpoint placed on an empty source line is automatically
  moved to the next statement.  A silly bug that made many $target
  variables inaccessible to .statement() probes was also fixed.

- LKET has been retired.  Please let us know on <systemtap@sourceware.org>
  if you have been a user of the tapset/tools, so we can help you find
  another way.

- New families of printing functions println() and printd() have been added.
  println() is like print() but adds a newline at the end;
  printd() is like a sequence of print()s, with a specified field delimiter.

* What's new since version 0.5.14?

- The way in which command line arguments for scripts are substituted has
  changed.  Previously, $1 etc. would interpret the corresponding command
  line argument as an numeric literal, and @1 as a string literal.  Now,
  the command line arguments are pasted uninterpreted wherever $1 etc.
  appears at the beginning of a token.  @1 is similar, but is quoted as
  a string.  This change does not modify old scripts, but has the effect
  of permitting substitution of arbitrary token sequences.

  # This worked before, and still does:
  % stap -e 'probe timer.s($1) {}'        5
  # Now this also works:
  % stap -e 'probe syscall.$1 {log(@1)}'  open
  # This won't crash, just signal a recursion error:
  % stap -e '$1'                          '$1'
  # As before, $1... is recognized only at the beginning of a token
  % stap -e 'probe begin {foo$1=5}'

* What's new since version 0.5.13?

- The way in which systemtap resolves function/inline probes has changed:
   .function(...) - now refers to all functions, inlined or not
   .inline(...)   - is deprecated, use instead:
   .function(...).inline - filters function() to only inlined instances
   .function(...).call - filters function() to only non-inlined instances
   .function(...).return - as before, but now pairs best with .function().call
   .statement() is unchanged.

* What's new since version 0.5.12?

- When running in -p4 (compile-only) mode, the compiled .ko file name
  is printed on standard output.

- An array element with a null value such as zero or an empty string
  is now preserved, and will show up in a "foreach" loop or "in" test.
  To delete such an element, the scripts needs to use an explicit
  "delete array[idx]" statement rather than something like "array[idx]=0".

- The new "-P" option controls whether prologue searching heuristics
  will be activated for function probes.  This was needed to get correct
  debugging information (dwarf location list) data for $target variables.
  Modern compilers (gcc 4.1+) tend not to need this heuristic, so it is
  no longer default.  A new configure flag (--enable-prologues) restores
  it as a default setting, and is appropriate for older compilers (gcc 3.*).

- Each systemtap module prints a one-line message to the kernel informational
  log when it starts.  This line identifies the translator version, base
  address of the probe module, a broken-down memory consumption estimate, and
  the total number of probes.  This is meant as a debugging / auditing aid.

- Begin/end probes are run with interrupts enabled (but with
  preemption disabled).  This will allow begin/end probes to be
  longer, to support generating longer reports.

- The numeric forms of kernel.statement() and kernel.function() probe points
  are now interpreted as relocatable values - treated as relative to the
  _stext symbol in that kernel binary.  Since some modern kernel images
  are relocated to a different virtual address at startup, such addresses
  may shift up or down when actually inserted into a running kernel.

     kernel.statement(0xdeadbeef): validated, interpreted relative to _stext,
                                   may map to 0xceadbeef at run time.

  In order to specify unrelocated addresses, use the new ".absolute"
  probe point suffix for such numeric addresses.  These are only
  allowed in guru mode, and provide access to no $target variables.
  They don't use debugging information at all, actually.

     kernel.statement(0xfeedface).absolute: raw, unvalidated, guru mode only

* What's new since version 0.5.10?

- Offline processing of debugging information, enabling general
  cross-compilation of probe scripts to remote hosts, without
  requiring identical module/memory layout.  This slows down
  compilation/translation somewhat.

- Kernel symbol table data is loaded by staprun at startup time
  rather than compiled into the module.

- Support the "limit" keyword for foreach iterations:
    foreach ([x,y] in ary limit 5) { ... }
  This implicitly exits after the fifth iteration.  It also enables
  more efficient key/value sorting.

- Support the "maxactive" keyword for return probes:
    probe kernel.function("sdfsdf").maxactive(848) { ... }
  This allows up to 848 concurrently outstanding entries to
  the sdfsdf function before one returns.  The default maxactive
  number is smaller, and can result in missed return probes.

- Support accessing of saved function arguments from within
  return probes.  These values are saved by a synthesized
  function-entry probe.

- Add substantial version/architecture checking in compiled probes to
  assert correct installation of debugging information and correct
  execution on a compatible kernel.

- Add probe-time checking for sufficient free stack space when probe
  handlers are invoked, as a safety improvement.

- Add an optional numeric parameter for begin/end probe specifications,
  to order their execution.
     probe begin(10) { } /* comes after */ probe begin(-10) {}

- Add an optional array size declaration, which is handy for very small
  or very large ones.
     global little[5], big[20000]

- Include some example scripts along with the documentation.

- Change the start-time allocation of probe memory to avoid causing OOM
  situations, and to abort cleanly if free kernel memory is short.

- Automatically use the kernel DWARF unwinder, if present, for stack
  tracebacks.

- Many minor bug fixes, performance, tapset, and error message
  improvements.