What is SEGV_MAPERR?

Question

What is SEGV_MAPERR, why does it always come up with SIGSEGV?

Answer 1

There are two common kinds of SEGV, which is an error that results from an invalid memory access:

1. A page was accessed which had the wrong permissions. E.g., it was read-only but your code tried to write to it. This will be reported as SEGV_ACCERR.
2. A page was accessed that is not even mapped into the address space of the application at all. This will often result from dereferencing a null pointer or a pointer that was corrupted with a small integer value. This is reported as SEGV_MAPERR.

Documentation of a sort (indexed Linux source code) for SEGV_MAPERR is here: http://lxr.free-electrons.com/ident?i=SEGV_MAPERR.