It's starting to look like upgrading to VS 2008 might be a winner for
this. I'm more willing to make this change than switch to the new
version of SysFile. Can the two version coexist on the same machine,
or do I need to uninstall 2005 first?
Rick
On Sat, Apr 25, 2009 at 11:23 PM, Mark Miesfeld <miesf...@gmail.com> wrote:
> Rick,
>
> In working on the SysFileSearch bug, I tracked down what seems to be a
> case where the VS 2005 compiler produces wrong code and the VS 2008
> produces code that works.
>
> It's bizarre, so it takes a bit to explain it. On Vista 64-bit, the
> GetLine() function causes a memory exception here:
>
> scan = (char *)memchr(filedata->scan, CH_NL, filedata->data);
>
> The exception comes because it has gone past the end of the file
> buffer. The check for the end of the buffer is right before, and the
> whole thing looks like:
>
> if (!(filedata->data)) { /* if out of current buffer */
> if (filedata->residual) { /* may be another buffer */
> ReadNextBuffer(filedata); /* try to read one */
> if (!filedata->data) /* nothing more? */
> return true; /* all done */
> }
> else
> return true; /* return EOF condition */
> }
> /* look for a carriage return */
> scan = (char *)memchr(filedata->scan, CH_NL, filedata->data);
>
> filedata->data keeps track of where in the buffer we are and when it
> is 0, we've used up the buffer.
>
> The bizarre thing is, when I compile with Visual Studio 2005, when
> filedata->data == 0, the if !(filedata->data) test passes and the
> function keeps going on past the end of the buffer. Eventually,
> memchr goes to compare memory it can't access.
>
> If I compile with Visual Studio 2008, then things work as they should.
> This is with the no debug build only. The debug build works fine
> when compiled with either VS 2005 or VS 2008.
>
> I sent you a text file with a lot output. It is easier to read when
> the lines don't wrap.
>
> I used this printf to show this behaviour:
>
> printf("GetLine: size=%u scan=%p filedata->data=%u residual=%u
> filedata->data == 0 ? %d\n",
> filedata->size, filedata->scan, filedata->data,
> filedata->residual, (filedata->data == 0));
>
>
> For the build that crashes you see this:
>
> GetLine: size=31452 scan=00000000001E9FDC filedata->data=0 residual=0
> filedata->data == 0 ? 0
> GetLine: size=31452 scan=00000000001EE48D filedata->data=4294949711
> residual=0 filedata->data == 0 ? 0
>
> You see that even though filedata->data does equal 0, (filedata->data
> == 0) returns 0.
>
> So, SysFileSearch keeps calling GetLine() until you finally reach
> memory that is not accessible.
>
> This only happens on Vista 64-bit, only on a no debug build, and only
> when the compiler is VS 2005. On XP 64-bit it works fine with either
> compiler. Also on 32-bit Vista it works fine with either compiler.
>
> If there was the same problem on Vista 32 bit, i.e. it crashed with
> the VS 2005 compiled version but worked with the VS 2008, then I was
> thinking maybe a similar thing is happening with Mike's problem.
> Still, if Mike can not reproduce his problem using the VS 2008
> compiled version, then maybe it is a similar thing.
>
> --
> Mark Miesfeld
>
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