docs/internals/xml-output-protocol4.txt

====================================================================

14 October 2011

Protocols 1 through 3 supported Memcheck only.  Protocol 4 provides
XML output for Memcheck, Helgrind, DRD and SGcheck.  Technically there
are four variants of Protocol 4, one for each tool, since they
produce different errors.  The four variants differ only in the
definition of the ERROR nonterminal and are otherwise identical.

NOTE that Protocol 4 (for the current svn trunk, which will eventually
become 3.7.x) is still under development.  The text herein should not
be regarded as the final definition.


Identification of Protocols
~~~~~~~~~~~~~~~~~~~~~~~~~~~

In Protocols 1 through 3, a <protocolversion>INT<protocolversion>
close to the start of the stream makes it possible for parsers to
ascertain the version, so they can tell whether or not they can handle
it.  The presence of support for multiple tools brings a complication,
though: it is not enough merely to state the protocol version -- the
tool name must also be stated.  Hence in Protocol 4, the
<protocolversion>INT<protocolversion> is followed immediately by
<protocoltool>TEXT</protocoltool>, to identify the tool.

This duplicates the tool name present later in the preamble, but it
was felt important to place the tool name right at the front along
with the protocol number, for easy determination of parseability.


How this specification is structured
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The TOPLEVEL nonterminal specifies top level XML output structure.  It
is common to all error producing tools.

TOPLEVEL references TOOLSPECIFICs for each tool, and these are defined
differently for each tool.  Each TOOLSPECIFIC is an error, which is
tool-specific.  For Helgrind and DRD, a TOOLSPECIFIC may also contain a
so-called thread-announcement record (described below).

Overall there is a very high degree of format commonality between the
three tools.  Once a GUI is able to display the output correctly for
one tool, it should be easy to extend it for the other two.


Protocol 4 changes for Memcheck
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Protocol 4 for Memcheck is similar to Protocol 3, but has a number
of changes to make it fit in the common framework:

- the SUPPCOUNTS nonterminal now appears after the "Zero or more
  ERRORs" block, and not before it.

- the abovementioned "Zero or more ERRORs" block now becomes
  "Zero or more of (either ERROR or ERRORCOUNTS)".

- ERRORs for Memcheck may contain a SUPPRESSION field, which gives
  the corresponding suppression for it.

- ERRORs for Memcheck now use the XWHAT and XAUXWHAT nonterminals, as
  well as WHAT and XWHAT.

- The ad-hoc blocks <leakedbytes> and <leakedblocks> used by Memcheck
  have been moved inside the XWHAT for the relevant error kinds.  This
  facilitates a common definition of ERROR across all three tools.

The first two changes are required in order to correct a longstanding
design flaw in the way Memcheck interacts with Valgrind's error
management mechanism.  See bug #186790
(https://bugs.kde.org/show_bug.cgi?id=186790).  The third change was
requested in #191189 (https://bugs.kde.org/show_bug.cgi?id=191189).

For GUI authors upgrading from Protocol 3 or earlier, the most
significant new concept to grasp is the relationship between WHAT and
XWHAT, and between AUXWHAT and XAUXWHAT.

The definition of Protocol 4 now follows.  It is structured similarly
to that of the previous protocols, except that there is a separate
definition of a nonterminal called TOOLSPECIFIC for each of Memcheck,
Helgrind, DRD and SGcheck.  The XWHAT and XAUXWHAT nonterminals also
have tool-specific components.  Apart from that, the structure is
common to all supported tools.


====================================================================

TOPLEVEL
--------

The first line output is always this:

   <?xml version="1.0"?>

All remaining output is contained within the tag-pair
<valgrindoutput>.

Inside that, the first entity is an indication of the protocol
version.  This is provided so that existing parsers can identify XML
created by future versions of Valgrind merely by observing that the
protocol version is one they don't understand.  Hence TOPLEVEL is:

  <?xml version="1.0"?>
  <valgrindoutput>
    <protocolversion>INT<protocolversion>
    <protocoltool>TEXT</protocoltool>
    PROTOCOL
  </valgrindoutput>

Valgrind versions 3.0.0 and 3.0.1 emit protocol version 1.  Versions
3.1.X and 3.2.X [and 3.3.X ??] emit protocol version 2.  3.4.X emits
protocol version 3.  3.5.X emits version 4.

The TEXT in <protocoltool> is either "memcheck", "helgrind", "drd" or
"exp-ptrcheck" and determines the allowed format of the ERROR
nonterminal.  Note that <protocoltool> is only present when the
protocol version is 4 or above.


PROTOCOL for version 4
----------------------

This is the main top-level construction.  Roughly speaking, it
contains a preamble, a program-started marker, the errors from the run
of the program, a program-ended marker, and any further errors
resulting from post-run analysis (eg, memory leak detection).  Hence
the following in sequence:

* Various preamble lines which give version info for the various
  components.  The text in them can be anything; it is not intended
  for interpretation by the GUI:

     <preamble>
        <line>Misc version/copyright text</line>  (zero or more of)
     </preamble>

* The PID of this process and of its parent:

     <pid>INT</pid>
     <ppid>INT</ppid>

* The name of the tool being used:

     <tool>TEXT</tool>

  This can be anything, and it doesn't have to match the
  <protocoltool> entry, although that might be wise.

* Zero or more bindings of environment variable names to actual
  values.  These describe precisely the instantiations of %q format
  specifiers used in the --xml-file= argument for the run, if any.
  There is one <logfilequalifier> entry for each %q expanded:

     <logfilequalifier> <var>VAR</var> <value>$VAR</value>
     </logfilequalifier>

* OPTIONALLY, if --xml-user-comment=STRING was given:

     <usercomment>STRING</usercomment>

  STRING is not escaped in any way, so that it itself may be a piece
  of XML with arbitrary tags etc.

* The program and args: first those pertaining to Valgrind itself, and
  then those pertaining to the program to be run under Valgrind (the
  client):

     <args>
       <vargv>
         <exe>TEXT</exe>
         <arg>TEXT</arg> (zero or more of)
       </vargv>
       <argv>
         <exe>TEXT</exe>
         <arg>TEXT</arg> (zero or more of)
       </argv>
     </args>

* The following, indicating that the program has now started:

     <status> <state>RUNNING</state>
              <time>human-readable-time-string</time>
     </status>

  The format of this string is not defined, but it is expected to be
  human-understandable.  In current Valgrind versions it is the
  elapsed wallclock time since process start.

* Zero or more of (either ERRORCOUNTS or TOOLSPECIFIC).

* The following, indicating that the program has now finished, and
  that the any final wrapup (eg, for Memcheck, leak checking) is happening.

     <status> <state>FINISHED</state>
              <time>human-readable-time-string</time>
     </status>

* Zero or more of (either ERRORCOUNTS or TOOLSPECIFIC).  In Memcheck's
  case these will be complaints from the leak checker.  For SGcheck
  and Helgrind we don't expect any output here (but the spec does not
  guarantee that either).

* SUPPCOUNTS, indicating how many times each suppression was used.


That's it.  The tool-specific definitions for TOOLSPECIFIC are below;
however let's first continue with some smaller nonterminals used in
the construction of errors for all the tool types.


====================================================================

Nonterminals used in construction of ERRORs
-------------------------------------------

STACK
-----
STACK indicates locations in the program being debugged.  A STACK
is one or more FRAMEs.  The first is the innermost frame, the
next its caller, etc.

   <stack>
      one or more FRAME
   </stack>


FRAME
-----
FRAME records a single program location:

   <frame>
      <ip>HEX64</ip>
      optionally <obj>TEXT</obj>
      optionally <fn>TEXT</fn>
      optionally <dir>TEXT</dir>
      optionally <file>TEXT</file>
      optionally <line>INT</line>
   </frame>

Only the <ip> field is guaranteed to be present.  It indicates a
code ("instruction pointer") address.

The optional fields, if present, appear in the order stated:

* obj: gives the name of the ELF object containing the code address

* fn: gives the name of the function containing the code address

* dir: gives the source directory associated with the name specified
       by <file>.  Note the current implementation often does not
       put anything useful in this field.

* file: gives the name of the source file containing the code address

* line: gives the line number in the source file


ERRORCOUNTS
-----------
This specifies, for each error that has been so far presented,
the number of occurrences of that error.

  <errorcounts>
     zero or more of
        <pair> <count>INT</count> <unique>HEX64</unique> </pair>
  </errorcounts>

Each <pair> gives the current error count <count> for the error with
unique tag </unique>.  The counts do not have to give a count for each
error so far presented - partial information is allowable.

As at Valgrind rev 3793, error counts are only emitted at program
termination.  However, it is perfectly acceptable to periodically emit
error counts as the program is running.  Doing so would facilitate a
GUI to dynamically update its error-count display as the program runs.


SUPPCOUNTS
----------
A SUPPCOUNTS block appears exactly once, after the program terminates.
It specifies the number of times each error-suppression was used.
Suppressions not mentioned were used zero times.

  <suppcounts>
     zero or more of
        <pair> <count>INT</count> <name>TEXT</name> </pair>
  </suppcounts>

The <name> is as specified in the suppression name fields in .supp
files.


SUPPRESSION
-----------
These are optionally emitted as part of ERRORs, and specify the
suppression that would be needed to suppress the containing error.
For convenience, the suppression is presented twice, once in
a structured nicely wrapped up in tags, and once as raw text
suitable for direct copying and pasting into a suppressions file.

  <suppression>
    <sname>TEXT</sname>    name of the suppression
    <skind>TEXT</skind>    kind, eg                 "Memcheck:Param"
    <skaux>TEXT</skaux>    (optional) aux kind, eg  "write(buf)"
    SFRAME                 (one or more) frames
    <rawtext> CDATAS </rawtext>
  </suppression>

where CDATAS is a sequence of one or more <![CDATA[ .. ]]> blocks
holding the raw text.  Unfortunately, CDATA provides no way to escape
the ending marker "]]>", which means that if the raw data contains
such a sequence, it has to be split between two CDATA blocks, one
ending with data "]]" and the other beginning with data "<".  This is
why the spec calls for one or more CDATA blocks rather than exactly
one.

Note that, so far, we cannot envisage a circumstance in which a
generated suppression would contain the string "]]>", since neither
"]" nor ">" appear to turn up in mangled symbol names.  Hence it is
not envisaged that there will ever be more than one CDATA block, and
indeed the implementation as of Valgrind 3.5.0 will only ever generate
one block (it ignores any possible escaping problems).  Nevertheless
the specification allows multiple blocks, as a matter of safety.


SFRAME
------
Either

  <sframe> <obj>TEXT</obj> </sframe>

eg denoting "obj:/usr/X11R6/lib*/libX11.so.6.2", or

  <sframe> <fun>TEXT</fun> </sframe>

eg denoting "fun:*libc_write"


WHAT and XWHAT
--------------

WHAT supplies a single line of text, which is a human-understandable,
primary description of an error.

XWHAT is an extended version of WHAT.  It also contains a piece of
text intended for human reading, but in addition may contain arbitrary
other tagged data.  This extra data is tool-specific.  One of its
purposes is to supply GUIs with links to other data in the sequence of
TOOLSPECIFICs, that are associated with the error.  Another purpose is
wrap certain quantities (numbers, file names, etc) embedded in the
message, so that the GUIs can get hold of them without having to parse
the text itself.

For example, we could get:

  <what>Possible data race on address 0x12345678</what>

or alternatively

  <xwhat>
     <text>Possible data race by thread #17 on address 0x12345678</text>
     <threadid>17</threadid>
  </xwhat>

And presumably the <threadid>17</threadid> refers to some previously
emitted entity in the stream of TOOLSPECIFICs for this tool.

In an XWHAT, the <text> tag-pair is mandatory.  GUIs which don't want
to handle the extra fields can just ignore them and display the text
part.  In this way they have the option to present at least something
useful to the user even in the case where the extra fields can't be
handled, for whatever reason.

A corollary of this is that the degenerate extended case

   <xwhat> <text>T</text> </xwhat>

is exactly equivalent to

   <what>T</what>


AUXWHAT and XAUXWHAT
--------------------

AUXWHAT is exactly like WHAT: a single line of text.  It provides
additional, secondary description of an error, that should be shown to
the user.

XAUXWHAT relates to AUXWHAT in the same way XWHAT relates to WHAT: it
wraps up extra tagged info along with the line of text that would be
in the AUXWHAT.


====================================================================

ERROR definition -- common structure
------------------------------------

ERROR defines an error, and is the most complex nonterminal.  For all
of the tools, the structure is common, and always conforms to the
following:

  <error>
     <unique>HEX64</unique>
     <tid>INT</tid>
     <kind>KIND</kind>

     (either WHAT or XWHAT)
     optionally: (either WHAT or XWHAT)

     STACK

     zero or more: (either AUXWHAT or XAUXWHAT or STACK)

     optionally: SUPPRESSION
  </error>


* Each error contains a unique, arbitrary 64-bit hex number.  This is
  used to refer to the error in ERRORCOUNTS nonterminals (see above).

* The <tid> tag indicates the Valgrind thread number.  This value
  is arbitrary but may be used to determine which threads produced
  which errors (at least, the first instance of each error).

* The <kind> tag specifies one of a small number of fixed error types,
  so that GUIs may roughly categorise errors by type if they want.
  The tags themselves are tool-specific and are defined further
  below, for each tool.

* The "(either WHAT or XWHAT)" gives a primary description of the
  error.  WHAT and XWHAT are defined earlier in this file.  Any XWHATs
  appearing here may contain tool-specific subcomponents.

* Optionally, a second line of primary description may be present.

* A STACK gives the primary source location for the error.

* There then follow zero or more of "(either AUXWHAT or XAUXWHAT or
  STACK)".  These give further (auxiliary) information about the
  error, possibly including stack traces.  They should be shown to the
  user in the order they appear.  AUXWHAT and XAUXWHAT are defined
  earlier in this file.  Any XAUXWHATs appearing here may contain
  tool-specific subcomponents.

* Optionally, as the last field, a SUPPRESSION may be provided.  This
  contains a suppression that would hide the error.


====================================================================

TOOLSPECIFIC definition for Memcheck
------------------------------------

For Memcheck, a TOOLSPECIFIC is simply an ERROR:

TOOLSPECIFIC = ERROR


ERROR details for Memcheck
--------------------------

XWHATs (for definition, see above) may contain the following extra
components (along with the mandatory <text>...</text> component):

* <leakedbytes>INT</leakedbytes>

* <leakedblocks>INT</leakedblocks>

These fields are used in errors that have a <kind> tag specifying a
KIND of the form "Leak_*", to indicate the number of leaked bytes and
blocks.


XAUXWHATs (for definition, see above) may contain the following extra
components (along with the mandatory <text>...</text> component):

* <file>TEXT</file>, as defined in FRAME

* <line>INT</line>, as defined in FRAME

* <dir>TEXT</dir>, as defined in FRAME


KIND for Memcheck
-----------------

This is a small enumeration indicating roughly the nature of an error.
The possible values are:

   InvalidFree

      free/delete/delete[] on an invalid pointer

   MismatchedFree

      free/delete/delete[] does not match allocation function
      (eg doing new[] then free on the result)

   InvalidRead

      read of an invalid address

   InvalidWrite

      write of an invalid address

   InvalidJump

      jump to an invalid address

   Overlap

      args overlap other otherwise bogus in eg memcpy

   InvalidMemPool

      invalid mem pool specified in client request

   UninitCondition

      conditional jump/move depends on undefined value

   UninitValue

      other use of undefined value (primarily memory addresses)

   SyscallParam

      system call params are undefined or point to
      undefined/unaddressible memory

   ClientCheck

      "error" resulting from a client check request

   Leak_DefinitelyLost

      memory leak; the referenced blocks are definitely lost

   Leak_IndirectlyLost

      memory leak; the referenced blocks are lost because all pointers
      to them are also in leaked blocks

   Leak_PossiblyLost

      memory leak; only interior pointers to referenced blocks were
      found

   Leak_StillReachable

      memory leak; pointers to un-freed blocks are still available


====================================================================

TOOLSPECIFIC definition for SGcheck
-----------------------------------

For SGcheck, a TOOLSPECIFIC is simply an ERROR:

TOOLSPECIFIC = ERROR


ERROR details for SGcheck
-------------------------

SGcheck does not produce any XWHAT records, despite the fact that
"ERROR definition -- common structure" says that tools may do so.


XAUXWHATs (for definition, see above) may contain the following extra
components (along with the mandatory <text>...</text> component):

* <file>TEXT</file>, as defined in FRAME

* <line>INT</line>, as defined in FRAME

* <dir>TEXT</dir>, as defined in FRAME


KIND for SGcheck
----------------
This is a small enumeration indicating roughly the nature of an error.
The possible values are:

   SorG

      Stack or global array inconsistency (roughly speaking, an
      overrun of a stack or global array).  The <auxwhat> blocks give
      further details.


====================================================================

TOOLSPECIFIC definition for Helgrind
-------------------------------------

For Helgrind, a TOOLSPECIFIC may be one of two things:

TOOLSPECIFIC = either ERROR or ANNOUNCETHREAD


ANNOUNCETHREAD
--------------

The definition is

   <announcethread>
      <hthreadid>INT</hthreadid>
      STACK
   </announcethread>

This states the creation point of a thread, and gives it a unique
"hthreadid", which may be referred to in subsequent ERRORs.  Note that

1. The appearance of ANNOUNCETHREAD does not mean that the thread was
   actually created at that point relative to any preceding or
   following ERRORs in the output stream -- in general the thread will
   have been created arbitrarily earlier.  Helgrind only "announces" a
   thread when it needs to refer to it for the first time, in a
   subsequent ERROR.

2. The "hthreadid" is a number which uniquely identifies the thread
   for the run - no other thread will have the same hthreadid.  The
   hthreadid is a Helgrind-specific piece of information and is
   unrelated to the <tid> fields in the common part of an ERROR.
   Be careful not to confuse the two.


ERROR details for Helgrind
--------------------------

XWHATs (for definition, see above) may contain the following extra
components (along with the mandatory <text>...</text> component):

* <hthreadid>INT</hthreadid> fields.  These refer to ANNOUNCETHREADs
  appearing previously in the scheme, and state the creation points of
  the thread(s) concerned in the ERROR.  Hence it should be possible
  for GUIs to show users stacks of the creation points of all threads
  involved in each ERROR.


XAUXWHATs (for definition, see above) may contain the following extra
components (along with the mandatory <text>...</text> component):

* <hthreadid>INT</hthreadid>, same meaning as when referred to in
  XWHAT

* <file>TEXT</file>, as defined in FRAME

* <line>INT</line>, as defined in FRAME

* <dir>TEXT</dir>, as defined in FRAME


KIND for Helgrind
-----------------
This is a small enumeration indicating roughly the nature of an error.
The possible values are:

   Race

      Data race.  Helgrind will try to show the stacks for both
      conflicting accesses if it can; it will always show the stack
      for at least one of them.

   UnlockUnlocked

      Unlocking a not-locked lock

   UnlockForeign

      Unlocking a lock held by some other thread

   UnlockBogus

      Unlocking an address which is not known to be a lock

   PthAPIerror

      One of the POSIX pthread_ functions that are intercepted
      by Helgrind, failed with an error code.  Usually indicates
      something bad happening.

   LockOrder

      An inconsistency in the acquisition order of locks was observed;
      dangerous, as it can potentially lead to deadlocks

   Misc

      One of various miscellaneous noteworthy conditions was observed
      (eg, thread exited whilst holding locks, "impossible" behaviour
      from the underlying threading library, etc)