Define MAP_NORESERVE to zero for FreeBSD

[dim]

Summary

The MAP_NORESERVE define has been removed in FreeBSD 11.x, and even
before that, it was never implemented. Just define it to zero instead,
so compiler-rt can compile on FreeBSD 11 and later.

[kutuzov.viktor.84]

Looks OK to me.

[samsonov]

I'm relying on Viktor's judgement here. Feel free to submit.

[kcc]

How does this all work then?
We need MAP_NORESERVE on Linux to map 20Tb for the asan process.
What's different on FreeBSD?

[dim]

In D7485#124902, @kcc wrote:

How does this all work then?
We need MAP_NORESERVE on Linux to map 20Tb for the asan process.
What's different on FreeBSD?

The MAP_NORESERVE and MAP_RENAME flags were retired here: https://reviews.freebsd.org/rS273250

Apparently they were never implemented on FreeBSD, at least not with Linux semantics. As far as I understand, FreeBSD doesn't have the functionality of signalling the affected process, instead of blocking for a page.

lib/sanitizer_common/sanitizer_posix.cc

 #if SANITIZER_LINUX
 #include <sys/utsname.h>
 #endif
 
 #if SANITIZER_LINUX && !SANITIZER_ANDROID
 #include <sys/personality.h>
 #endif
 
+#if SANITIZER_FREEBSD
+// The MAP_NORESERVE define has been removed in FreeBSD 11.x, and even before
+// that, it was never implemented.  So just define it to zero.
+#undef  MAP_NORESERVE
+#define MAP_NORESERVE 0
+#endif
+
 namespace __sanitizer {
 
 // ------------- sanitizer_common.h
 uptr GetMmapGranularity() {
   return GetPageSize();
 }
 
 #if SANITIZER_WORDSIZE == 32