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47251Re: running valgrind with vim

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  • Bram Moolenaar
    Aug 5, 2007
    • 0 Attachment
      Dominique Pelle wrote:

      > > > Hi,
      > > >
      > > > Valgrind memory checker finds several errors in vim-7.1 (patches 1-50)
      > > > when built with --enable-multibyte:
      > > >
      > > > $ ./configure --enable-multibyte
      > > > $ make CFLAGS="-O0 -g"
      > > > $ cd src/testdir
      > > > $ valgrind ../vim -u unix.vim -U NONE --noplugin -s dotest.in
      > > > test45.in 2> valgrind-test45.txt
      >
      > ...
      >
      > > It's a lot of work to check out the warnings, so please make sure there
      > > are no false warnings.
      >
      >
      > I believe I have a patch to fix errors reported by valgrind in test case 45
      > but please review it.
      >
      > Error was:
      >
      > ==14428== Conditional jump or move depends on uninitialised value(s)
      > ==14428== at 0x80FDD10: utfc_ptr2len (mbyte.c:1676)
      > ==14428== by 0x813EB6B: win_line (screen.c:3586)
      > ==14428== by 0x813BBF0: win_update (screen.c:1760)
      > ==14428== by 0x8139FFE: update_screen (screen.c:522)
      > ==14428== by 0x80CD1CF: main_loop (main.c:1088)
      > ==14428== by 0x80CCF72: main (main.c:939)
      > etc.
      >
      > Variable p_extra at screen.c:3586 was initialized by fill_foldcolumn()
      > with 'foldcolumn' spaces (3 spaces in test case 45). 'p_extra' pointer
      > is actually in this case the local 'extra' array. The rest of 'p_extra'
      > buffer is uninitialized. vim_line() then loops on those 3 spaces but
      > accesses the next characters inside utfc_ptr2len() when multi_byte
      > is enabled, hence causing valgrind to complain when displaying
      > the last space.
      >
      > Bug can be simply triggered when doing ":set foldcolumn" and when
      > vim was built 'multi_byte'. The following command is enough to trigger
      > an error with valgrind:
      >
      > $ vim -u NONE -c 'set foldcolumn=4' 2> valgrind.log
      >
      > I attach the patch to fix the problem. It basically adds NUL character
      > at the end of 'foldcolumn' spaces when. This patch actually fixes all errors
      > reported by valgrind in test case 45.
      >
      > Without patch, bahavior of calling utfc_ptr2len() at line screen.c:3586
      > may be undetermined. It's also slower since it may need to call
      > utf_ptr2len() whereas with patch, function utfc_ptr2len() returns
      > immediately at mbyte.c:1676.

      Thanks for digging into this.

      I spotted a few other places where p_extra may point to text that is not
      NUL terminated and where utfc_ptr2len() may not work correctly. That
      won't give an uninitialized read error, but it may still be wrong.

      --
      From "know your smileys":
      =):-) Uncle Sam

      /// Bram Moolenaar -- Bram@... -- http://www.Moolenaar.net \\\
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