Commits on Feb 6, 2016

1. Abort on stack overflow instead of re-raising SIGSEGV …

   We use guard pages that cause the process to abort to protect against
   undefined behavior in the event of stack overflow.  We have a handler
   that catches segfaults, prints out an error message if the segfault was
   due to a stack overflow, then unregisters itself and returns to allow
   the signal to be re-raised and kill the process.
   
   This caused some confusion, as it was unexpected that safe code would be
   able to cause a segfault, while it's easy to overflow the stack in safe
   code.  To avoid this confusion, when we detect a segfault in the guard
   page, abort instead of the previous behavior of re-raising the SIGSEGV.
   
   To test this, we need to adapt the tests for segfault to actually check
   the exit status.  Doing so revealed that the existing test for segfault
   behavior was actually invalid; LLVM optimizes the explicit null pointer
   reference down to an illegal instruction, so the program aborts with
   SIGILL instead of SIGSEGV and the test didn't actually trigger the
   signal handler at all.  Use a C helper function to get a null pointer
   that LLVM can't optimize away, so we get our segfault instead.
   
   This is a [breaking-change] if anyone is relying on the exact signal
   raised to kill a process on stack overflow.
   
   Closes rust-lang#31273

   

   lambda committed Feb 6, 2016
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