May 26, 2018

Debugging malloc() that uses the VM hardware to detect buffer overruns

Electric Fence is a different kind of malloc debugger. It uses the virtual memory hardware of your system to detect when software overruns the boundaries of a malloc buffer. It will also detect any accesses of memory that has been released by free. Because it uses the VM hardware for detection, Electric Fence stops your program on the first instruction that causes a bounds violation. It’s then trivial to use a debugger to display the offending statement.

It will probably port to any ANSI/POSIX system that provides mmap, and mprotect, as long as mprotect has the capability to turn off all access to a memory page, and mmap can use /dev/zero or the MAP_ANONYMOUS flag to create virtual memory pages.

Complete information on the use of Electric Fence is in the manual page efence3.