Dynamic memory allocation issue

Robert S. Grimes rsg at alum.mit.edu
Tue Jan 20 16:54:57 UTC 2009

I've run across this before, and I've used workarounds, later to find 
the problem went away.  I thought it was something I was doing wrong 
that I somehow stopped doing, as it didn't happen again for some 
weeks/months - until this morning.  I added code like this:

  uint8_t* faultTable_;

  printk("Getting new fault table of size %d\n", sizeInBytes_);
  faultTable_ = new uint8_t(sizeInBytes_);
  printk("Got new fault table (%p)\n", faultTable_);
  if (faultTable_) {
    printk("Initializing new fault table (%p), size %u\n",
           faultTable_, sizeInBytes_);
    memset(faultTable_, 0, sizeInBytes_);   // <<== This is the problem?
    printk("New fault table (%p) ready for use\n", faultTable_);
  } else {
    numFaults_ = sizeInBytes_ = 0;

Here is what I get:

  Getting new fault table of size 36
  Got new fault table (6C2D90)
  Initializing new fault table (6C2D90), size 36
  New fault table (6C2D90) ready for use
  PASS: 0 !front and back sizes don't match

The last line of the output is from the heap walker.

If I delete the call to memset(), the problem goes away.  This is (more 
surprisingly) even true if I defer the exact same call to memset() (i.e. 
with the same pointer and size arguments) until (much) later!

Oh, and it's not memset() per se, as a loop to clear the buffer at the 
same location fails the same way.

Any ideas?

Thanks in advance!

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