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Half Page

Question Text​

char *p = malloc(2 * 1024);

What is a potential problem when allocating half a page?

Question Answers​

  • It will fragment the virtual memory because users should always request at least one page

  • Asking for less than a page might place the memory on two different pages

  • Writing to the other half may be allowed
  • Allocations smaller than one page should use the stack

Feedback​

The OS allocates memory in chunks of 4 KB (the page size). If the memory we allocate happens to be placed at the beginning of a page, we have permission to update the second half of this page despite not requesting it. This might be a problem because buffer overflows can pass unnoticed.