Bug 3419 - Mono.Unix.Native.MmapFlags.MAP_ANON validation is wrong on Mac
Summary: Mono.Unix.Native.MmapFlags.MAP_ANON validation is wrong on Mac
Alias: None
Product: Class Libraries
Classification: Mono
Component: Mono.POSIX ()
Version: master
Hardware: PC Mac OS
: Normal normal
Target Milestone: Untriaged
Assignee: Jonathan Pryor
Depends on:
Reported: 2012-02-13 09:00 UTC by Rolf Bjarne Kvinge [MSFT]
Modified: 2012-02-27 17:43 UTC (History)
3 users (show)

Is this bug a regression?: ---
Last known good build:

Proposed patch (1.43 KB, patch)
2012-02-13 09:26 UTC, Rolf Bjarne Kvinge [MSFT]

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Description Rolf Bjarne Kvinge [MSFT] 2012-02-13 09:00:37 UTC
It's 0x1000 on Mac (x64 Lion), not 0x20 as in Linux.

Simple test program:

#include <sys/mman.h>

int main() {
        printf ("EXEC: %i R: %i W: %i MAP_ANON: 0x%x, MAP_PRIVATE: %i, sizeof(size_t): %i\n", PROT_EXEC, PROT_READ, PROT_WRITE, MAP_ANON, MAP_PRIVATE, sizeof (size_t));
    return 0;

Linux (x64): EXEC: 4 R: 1 W: 2 MAP_ANON: 0x1000, MAP_PRIVATE: 2, sizeof(size_t): 8
Mac (x64): EXEC: 4 R: 1 W: 2 MAP_ANON: 0x1000, MAP_PRIVATE: 2, sizeof(size_t): 8
Comment 1 Rolf Bjarne Kvinge [MSFT] 2012-02-13 09:01:12 UTC
err, c&p error, the correct is:

Linux: EXEC: 4 R: 1 W: 2 MAP_ANON: 0x20, MAP_PRIVATE: 2, sizeof(size_t): 8
Comment 2 Rolf Bjarne Kvinge [MSFT] 2012-02-13 09:26:11 UTC
Created attachment 1353 [details]
Proposed patch

The issue is really that the parameter validation is wrong. See attached patch for more information (in short it's impossible to pass MAP_ANON to mmap on a Mac).
Comment 3 Rolf Bjarne Kvinge [MSFT] 2012-02-20 19:25:48 UTC
So, map.c seems to be a generated file. The bug is still there though, even though the patch isn't the right one.
Comment 4 Miguel de Icaza [MSFT] 2012-02-25 01:17:13 UTC
But can you describe what the problem was?

The internal constants are not supposed to be a 1:1 mapping to the system constant, we have an intermediate layer that translates the C# values to the native values.
Comment 5 Rolf Bjarne Kvinge [MSFT] 2012-02-27 07:05:30 UTC
The problem is the parameter validation and the fact that two constants have the same value.

We fail validation if managed code sets a flag that doesn't exist in native code. We also have two flags with the same value (MAP_ANONYMOUS and MAP_ANON) in managed code. In OSX MAP_ANON doesn't exist (but MAP_ANONYMOUS does). Combining all this: when the managed MAP_ANON[YMOUS] flag is set, we enter the MAP_ANON validation in native code, which fails since MAP_ANON isn't defined on OSX.
Comment 6 Miguel de Icaza [MSFT] 2012-02-27 09:06:59 UTC
Jon, can you take over this?
Comment 7 Jonathan Pryor 2012-02-27 17:43:19 UTC
Fixed in master/163f9061

I didn't want to change map.c (it would get overwritten the next time create-native-map was executed), so I opted for the easier route of changing mph.h and having MAP_ANONYMOUS alias MAP_ANON:

+#endif  /* ndef MAP_ANONYMOUS */
+endif  /* ndef PLATFORM_MACOSX */