Add NetBSD support in asan_stack.h

[krytarowski]

Summary

Part of the code inspired by the original work on libsanitizer in GCC 5.4 by Christos Zoulas.

Sponsored by <The NetBSD Foundation>

[davide]

Kamil, a fair amount of these changes seem to just replace SANITIZER_FREEBSD with SANITIZER_FREEBSD || SANITIZER_NETBSD.
I wonder whether it makes sense to define a SANITIZER_BSD macro for both of them?

Also, what's the difference in support you expect between NetBSD and FreeBSD to support sanitizers?

[krytarowski]

In D36377#833523, @davide wrote:

Kamil, a fair amount of these changes seem to just replace SANITIZER_FREEBSD with SANITIZER_FREEBSD || SANITIZER_NETBSD.
I wonder whether it makes sense to define a SANITIZER_BSD macro for both of them?

Also, what's the difference in support you expect between NetBSD and FreeBSD to support sanitizers?

I oppose SANITIZER_BSD as I don't intend to test BSD/OS and similar systems.

FreeBSD and NetBSD are sufficiently distinct to be managed separately. Also there will certainly come at some point OpenBSD, which
is different than FreeBSD and NetBSD. I don't have access to other BSDs to test potential patches.

Solaris support as far as I recall, was very similar, mostly adding || SANITIZER_SOLARIS to existing code.

lib/asan/asan_stack.h

 #else
   AsanThread *t;
   stack->size = 0;
   if (LIKELY(asan_inited)) {
     if ((t = GetCurrentThread()) && !t->isUnwinding()) {
       // On FreeBSD the slow unwinding that leverages _Unwind_Backtrace()
       // yields the call stack of the signal's handler and not of the code
       // that raised the signal (as it does on Linux).
-      if (SANITIZER_FREEBSD && t->isInDeadlySignal()) fast = true;
+      if ((SANITIZER_FREEBSD || SANITIZER_NETBSD) && t->isInDeadlySignal())
+        fast = true;
       uptr stack_top = t->stack_top();
       uptr stack_bottom = t->stack_bottom();
       ScopedUnwinding unwind_scope(t);
       if (!SANITIZER_MIPS || IsValidFrame(bp, stack_top, stack_bottom)) {
         stack->Unwind(max_depth, pc, bp, context, stack_top, stack_bottom,
                       fast);
       }
     } else if (!t && !fast) {