[utils] Don't use MAP_32BIT on Apple platforms, fixes crash with XCode 11 beta6 ...

As of XCode 11 beta6 the MacOSX SDK defines the MAP_32BIT symbol:

```diff
--- /Applications/Xcode11-beta5.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/usr/include/sys/mman.h    2019-07-25 17:43:49.000000000 -0400
+++ /Applications/Xcode11-beta6.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/usr/include/sys/mman.h    2019-08-06 21:03:07.000000000 -0400
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved.
+ * Copyright (c) 2000-2019 Apple Computer, Inc. All rights reserved.
  *
  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
  *
@@ -145,6 +145,10 @@
 #define MAP_RESILIENT_CODESIGN  0x2000 /* no code-signing failures */
 #define MAP_RESILIENT_MEDIA     0x4000 /* no backing-store failures */

+#if !defined(CONFIG_EMBEDDED)
+#define MAP_32BIT       0x8000          /* Return virtual addresses <4G only: Requires entitlement */
+#endif  /* !defined(CONFIG_EMBEDDED) */
+
 #endif  /* (!_POSIX_C_SOURCE || _DARWIN_C_SOURCE) */

 /*
```

This causes the mono_valloc() function to try to use the MAP_32BIT flag for mmap().

However as mentioned in the comment for the symbol in mman.h it seems to require a special entitlement
which isn't available/documented anywhere yet.
This in turn causes the mmap call to fail presumably because we're missing that entitlement.

Instead we now skip setting this flag on Apple platforms to make mmap() behave like it did before.

Commit migrated from https://github.com/mono/mono/commit/2f2771fcfa22ac16a24a6a1ff2554440e5de29ca

diff --git a/src/mono/mono/utils/mono-mmap.c b/src/mono/mono/utils/mono-mmap.c
index 5ef36ee..3be70d9 100644 (file)
--- a/src/mono/mono/utils/mono-mmap.c
+++ b/src/mono/mono/utils/mono-mmap.c
@@ -51,9 +51,11 @@
 #define MAP_ANONYMOUS MAP_ANON
 #endif
 
+#if !defined(__APPLE__)  // returning virtual addresses <4G requires entitlement on Apple platforms, do not use it
 #ifndef MAP_32BIT
 #define MAP_32BIT 0
 #endif
+#endif
 
 typedef struct {
        int size;
@@ -277,8 +279,10 @@ mono_valloc (void *addr, size_t length, int flags, MonoMemAccountType type)
        /* translate the flags */
        if (flags & MONO_MMAP_FIXED)
                mflags |= MAP_FIXED;
+#if !defined(__APPLE__)  // returning virtual addresses <4G requires entitlement on Apple platforms, do not use it
        if (flags & MONO_MMAP_32BIT)
                mflags |= MAP_32BIT;
+#endif
 
 #ifdef HOST_WASM
        if (length == 0)
@@ -381,8 +385,10 @@ mono_file_map_error (size_t length, int flags, int fd, guint64 offset, void **re
                mflags |= MAP_SHARED;
        if (flags & MONO_MMAP_FIXED)
                mflags |= MAP_FIXED;
+#if !defined(__APPLE__)  // returning virtual addresses <4G requires entitlement on Apple platforms, do not use it
        if (flags & MONO_MMAP_32BIT)
                mflags |= MAP_32BIT;
+#endif
 
 #ifdef HOST_WASM
        if (length == 0)