Wireshark · Ethereal-dev: [Ethereal-dev] Patch for SigComp dissector

["Ollis, Paul" <paul.ollis@xxxxxxxxxx>]

Please find attached a patch file, which fixes a number of issues with
the
SigComp dissector. The text file provides details of all the changes.

Regards,
Paul Ollis

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Attachment: sigcomp.patch.gz
Description: sigcomp.patch.gz

Report of changes made to the Ethereal SigComp Dissector
========================================================

The following source files have been modified.
----------------------------------------------

    epan/sigcomp-udvm.c
    epan/sigcomp-udvm.h
    epan/sigcomp_state_hdlr.c
    epan/sigcomp_state_hdlr.h
    epan/dissectors/packet-sigcomp.c


Modifications details
---------------------

  epan/dissectors/packet-sigcomp.c
  --------------------------------

    Function dissect_sigcomp:

        1. Make sure the temporary buffer that is used to load byte-code from
           state is zeroed, since the function udvm_state_access implicitly
           relies on this.

        2. Pass the SigComp message header length, state length and partial
           state length to decompress_sigcomp_message.

        3. Removed the state_vars_valid parameter from calls to
           udvm_state_access.


  epan/sigcomp_state_hdlr.c epan/sigcomp_state_hdlr.h
  ---------------------------------------------------

    Function udvm_state_access:

        1. Removed the state_vars_valid parameter. It is no longer used.

        2. The function now correctly updates each of state_length,
           state_address and state_instruction with saved state value.

           [Previously this was only done for state referenced in the SigComp
            message header.]

        3. Removed code that (incorrectly) read byte_copy_left from UDVM memory
           within the loop that writes the state to UDVM memory.

        4. Removed the code that set the useful values in UDVM memory. This
           should only be done for state referenced in the SigComp message
           header. (The decompress_sigcomp_message function, sets the useful
           values.)


  epan/sigcomp-udvm.c epan/sigcomp-udvm.h
  ---------------------------------------

    Function decompress_sigcomp_message:

        1. Added three new parameters; header_len, byte_code_state_len,
           byte_code_id_len.  The byte_code_state_len and byte_code_id_len
           are used to set the useful values in UDVM memory. The
           header_len is required to calculate the cycles available
           for decompression.

        2. Various minor corrections to spellings, etc in generated
           messages.

        3. Reduced the number of lines of output for print_level_1. Now
           the execution trace shows the instruction name and parameter
           values on one line.

           [This was done because, we found that even at the lowest
           level of detail ethereal became unusably slow; running on
           a 500 MHz SPARC. This seems to be related to the number of
           lines produced by the SigComp trace, which can easily be over
           1000 with the modified code.]

        4. Removed the used of some floating point functions. In all
           cases they were unnecessary and could potentially cause the
           code to produce the wrong results on some platforms (although
           this is unlikely).

        5. The useful values are now set correctly, using the new
           byte_code_state_len and byte_code_id_len parameters.

        6. The message header length is now included in the calculation of
           maximum_UDVM_cycles. Previously, the calculation could underestimate
           the value, resulting in the (small) chance that some legitimate
           messages might fail to decompress.

           Note: The calculation might now slightly over-estimate the cycles
           but this is a reasonable thing to do.

        7. Implemented the PUSH, POP, CALL and RETURN instructions.

           Note: The two SORT instructions and the CRC and SHA-1 instructions
           are still not implemented.

        8. The COPY and COPY-LITERAL instructions now apply the
           byte-copying-rules to the source address as well as the destination
           address.

        9. The COPY-LITERAL and COPY-OFFSET now correctly handle the
           destination operand. Previously, it was possible for the destination
           to be left at byte_copy_right when it should be left at
           byte_copy_left.

        10. All three COPY instructions will now behave correctly if the source
            or destination start at byte_copy_right; i.e. they read/write to
            byte_copy_right, byte_copy_right+1, etc. Previously the parameters
            would wrap to byte_copy_left.

        11. The COPY-OFFSET instruction now correctly calculates the source
            address for all values of offset. Previously a very large offset
            (greater than the circular buffer size) could cause the starting
            position to be mis-calculated.

        12. Modulo 65536 arithmetic has been added in some places where it was
            missing.

            [Only when noticed, we have not been able to check all the code.]

        13. Some redundant code was removed for the INPUT-BITS instruction.
            Also, INPUT-BITS (0, x, x) now correctly discards spare bits when
            the P-bit, has changed.

        14. Corrected the cycles used calculation for the INPUT-BITS
            instruction.

        15. Corrected some minor cases where the used_udvm_cycles was not
            incremented.

            [Not really a problem, but it allowed us to verify correctness with
            some of the SigComp torture tests.]

        16. Removed some redundant code in INPUT-HUFFMAN (and reorganised some
            comments to keep them making sense).


    Function decomp_dispatch_get_bits:

        1. This has been rewritten. The original version could not correctly
           handle requests for more than 8 bits. The new version is cleaner and
           correctly handles all cases.