Clean up abort.
* A dlmalloc usage error shouldn't call abort(3) because we want to
cause a SIGSEGV by writing the address dlmalloc didn't like to an
address the kernel won't like, so that debuggerd will dump the
memory around the address that upset dlmalloc.
* Switch to the simpler FreeBSD/NetBSD style of registering stdio
cleanup. Hopefully this will let us simplify more of the stdio
* Clear the stdio cleanup handler before we abort because of a dlmalloc
corruption error. This fixes the reported bug, where we'd hang inside
dlmalloc because the stdio cleanup reentered dlmalloc.
11 files changed