On Mon, Nov 25, 2013 at 03:10:07PM -0700, Bob Proulx wrote:
In those systems the zero page is initially bit-zero and reading from the zero point will return zero values from the contents there. If the program writes to the zero page then subsequent reads will return whatever was written there. This is bad behavior that was the default due to bugs in much legacy software. Unmapping the zero page will cause those programs to segfault and therefore the vendors default to having the page mapped to avoid support calls from their customers.
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This is one of the areas that needs to be addressed when people port software developed on a legacy Unix system over to a GNU/Linux system. If the software wasn't written with this in mind then it might be buggy and will need runtime testing to verify it.
To be fair, the software was already buggy, and likely had nearly-impossible-to-diagnose runtime errors caused by null pointer derefs yielding whatever junk was left in memory.
Mike Stone