diff --git a/libmac/libc/darwin_errno_codes.h b/libmac/libc/darwin_errno_codes.h
new file mode 100644
index 000000000..2d18724e0
--- /dev/null
+++ b/libmac/libc/darwin_errno_codes.h
@@ -0,0 +1,115 @@
+#ifndef DARWIN_ERRNO_CODES_H
+#define DARWIN_ERRNO_CODES_H
+
+/* $ awk '/#define[ \t]([A-Z]+)[\t ]+([0-9]+)/ { print "#define DARWIN_" $2 " " $3; }' < errno.h */
+
+#define DARWIN_EPERM 1
+#define DARWIN_ENOENT 2
+#define DARWIN_ESRCH 3
+#define DARWIN_EINTR 4
+#define DARWIN_EIO 5
+#define DARWIN_ENXIO 6
+#define DARWIN_ENOEXEC 8
+#define DARWIN_EBADF 9
+#define DARWIN_ECHILD 10
+#define DARWIN_EDEADLK 11
+#define DARWIN_ENOMEM 12
+#define DARWIN_EACCES 13
+#define DARWIN_EFAULT 14
+#define DARWIN_ENOTBLK 15
+#define DARWIN_EBUSY 16
+#define DARWIN_EEXIST 17
+#define DARWIN_EXDEV 18
+#define DARWIN_ENODEV 19
+#define DARWIN_ENOTDIR 20
+#define DARWIN_EISDIR 21
+#define DARWIN_EINVAL 22
+#define DARWIN_ENFILE 23
+#define DARWIN_EMFILE 24
+#define DARWIN_ENOTTY 25
+#define DARWIN_ETXTBSY 26
+#define DARWIN_EFBIG 27
+#define DARWIN_ENOSPC 28
+#define DARWIN_ESPIPE 29
+#define DARWIN_EROFS 30
+#define DARWIN_EMLINK 31
+#define DARWIN_EPIPE 32
+#define DARWIN_EDOM 33
+#define DARWIN_ERANGE 34
+#define DARWIN_EAGAIN 35
+#define DARWIN_EINPROGRESS 36
+#define DARWIN_EALREADY 37
+#define DARWIN_ENOTSOCK 38
+#define DARWIN_EDESTADDRREQ 39
+#define DARWIN_EMSGSIZE 40
+#define DARWIN_EPROTOTYPE 41
+#define DARWIN_ENOPROTOOPT 42
+#define DARWIN_EPROTONOSUPPORT 43
+#define DARWIN_ESOCKTNOSUPPORT 44
+#define DARWIN_ENOTSUP 45
+#define DARWIN_EPFNOSUPPORT 46
+#define DARWIN_EAFNOSUPPORT 47
+#define DARWIN_EADDRINUSE 48
+#define DARWIN_EADDRNOTAVAIL 49
+#define DARWIN_ENETDOWN 50
+#define DARWIN_ENETUNREACH 51
+#define DARWIN_ENETRESET 52
+#define DARWIN_ECONNABORTED 53
+#define DARWIN_ECONNRESET 54
+#define DARWIN_ENOBUFS 55
+#define DARWIN_EISCONN 56
+#define DARWIN_ENOTCONN 57
+#define DARWIN_ESHUTDOWN 58
+#define DARWIN_ETOOMANYREFS 59
+#define DARWIN_ETIMEDOUT 60
+#define DARWIN_ECONNREFUSED 61
+#define DARWIN_ELOOP 62
+#define DARWIN_ENAMETOOLONG 63
+#define DARWIN_EHOSTDOWN 64
+#define DARWIN_EHOSTUNREACH 65
+#define DARWIN_ENOTEMPTY 66
+#define DARWIN_EPROCLIM 67
+#define DARWIN_EUSERS 68
+#define DARWIN_EDQUOT 69
+#define DARWIN_ESTALE 70
+#define DARWIN_EREMOTE 71
+#define DARWIN_EBADRPC 72
+#define DARWIN_ERPCMISMATCH 73
+#define _DARWIN_EPROGUNAVAIL 74
+#define _DARWIN_EPROGMISMATCH 75
+#define _DARWIN_EPROCUNAVAIL 76
+#define DARWIN_ENOLCK 77
+#define DARWIN_ENOSYS 78
+#define _DARWIN_EFTYPE 79
+#define _DARWIN_EAUTH 80
+#define _DARWIN_ENEEDAUTH 81
+#define _DARWIN_EPWROFF 82
+#define _DARWIN_EDEVERR 83
+#define DARWIN_EOVERFLOW 84
+#define _DARWIN_EBADEXEC 85
+#define _DARWIN_EBADARCH 86
+#define _DARWIN_ESHLIBVERS 87
+#define _DARWIN_EBADMACHO 88
+#define DARWIN_ECANCELED 89
+#define DARWIN_EIDRM 90
+#define DARWIN_ENOMSG 91
+#define DARWIN_EILSEQ 92
+#define _DARWIN_ENOATTR 93
+#define DARWIN_EBADMSG 94
+#define DARWIN_EMULTIHOP 95
+#define DARWIN_ENODATA 96
+#define DARWIN_ENOLINK 97
+#define DARWIN_ENOSR 98
+#define DARWIN_ENOSTR 99
+#define DARWIN_EPROTO 100
+#define DARWIN_ETIME 101
+#define DARWIN_EOPNOTSUPP 102
+#define _DARWIN_ENOPOLICY 103
+#define DARWIN_ENOTRECOVERABLE 104
+#define DARWIN_EOWNERDEAD 105
+#define _DARWIN_EQFULL 106
+#define _DARWIN_ELAST 106
+#define _DARWIN_ECVCERORR 256
+#define _DARWIN_ECVPERORR 512
+
+#endif
diff --git a/libmac/libc/directmap.lst b/libmac/libc/directmap.lst
new file mode 100644
index 000000000..1f7a5948e
--- /dev/null
+++ b/libmac/libc/directmap.lst
@@ -0,0 +1,2 @@
+__error;__errno_location
+
diff --git a/libmac/libc/errno.cpp b/libmac/libc/errno.cpp
new file mode 100644
index 000000000..6c80d62a1
--- /dev/null
+++ b/libmac/libc/errno.cpp
@@ -0,0 +1,71 @@
+#define _POSIX_C_SOURCE 200112L
+#undef _GNU_SOURCE // for proper strerror_r
+#include <errno.h>
+#include <cstring>
+#include <cstdio>
+#include "errno.h"
+#include "darwin_errno_codes.h"
+
+static void initErrnoMappingTable() __attribute__ ((constructor));
+static int darwin_to_linux[130];
+static int linux_to_darwin[130];
+
+// This is deprecated, we don't bother to support that
+extern "C" const char * const __darwin_sys_errlist[0];
+extern "C" const int __darwin_sys_nerr = 0;
+
+int cthread_errno()
+{
+	return errno;
+}
+
+void initErrnoMappingTable()
+{
+	::memset(darwin_to_linux, 0, sizeof(darwin_to_linux));
+	::memset(linux_to_darwin, 0, sizeof(linux_to_darwin));
+	
+#	include "darwin_to_linux.map"
+#	include "linux_to_darwin.map"
+
+	darwin_to_linux[_DARWIN_EBADEXEC] = ENOEXEC;
+	darwin_to_linux[_DARWIN_EBADARCH] = ENOEXEC;
+	darwin_to_linux[_DARWIN_EBADMACHO] = ENOEXEC;
+}
+
+int errnoDarwinToLinux(int err)
+{
+	if (err < sizeof(darwin_to_linux)/sizeof(darwin_to_linux[0])-1)
+		return darwin_to_linux[err];
+	else
+		return 0;
+}
+
+int errnoLinuxToDarwin(int err)
+{
+	if (err < sizeof(linux_to_darwin)/sizeof(linux_to_darwin[0])-1)
+		return linux_to_darwin[err];
+    else
+        return 0;
+}
+
+char* __darwin_strerror(int errnum)
+{
+	errnum = errnoDarwinToLinux(errnum);
+	return ::strerror(errnum);
+}
+
+int __darwin_strerror_r(int errnum, char *strerrbuf, size_t buflen)
+{
+	errnum = errnoDarwinToLinux(errnum);
+	return ::strerror_r(errnum, strerrbuf, buflen);
+}
+
+void __darwin_perror(const char *s)
+{
+	// First map the error back
+	errno = errnoDarwinToLinux(errno);
+	::perror(s);
+	// Now map it back again
+	errno = errnoLinuxToDarwin(errno);
+}
+
diff --git a/libmac/libc/errno.h b/libmac/libc/errno.h
new file mode 100644
index 000000000..aee18b565
--- /dev/null
+++ b/libmac/libc/errno.h
@@ -0,0 +1,16 @@
+#ifndef DARWIN_ERRNO_H
+#define DARWIN_ERRNO_H
+
+extern "C"
+{
+	// int *__error(); /* generated code */
+	int cthread_errno();
+	
+	char* __darwin_strerror(int errnum);
+	int __darwin_strerror_r(int errnum, char *strerrbuf, size_t buflen);
+}
+
+int errnoDarwinToLinux(int err);
+int errnoLinuxToDarwin(int err);
+
+#endif
diff --git a/tools/gendirectmapassembly b/tools/gendirectmapassembly
new file mode 100755
index 000000000..5264d1689
--- /dev/null
+++ b/tools/gendirectmapassembly
@@ -0,0 +1,23 @@
+#!/bin/bash
+
+# Generates a direct mapping between two functions in assembly code
+
+(
+echo "section .text"
+echo
+
+while read line; do
+	arrIN=(${line//;/ })
+
+	if [ ${#arrIN[@]} -ne 2 ]; then
+		continue
+	fi
+
+	echo "global ${arrIN[0]}"
+	echo "extern ${arrIN[1]}"
+	echo "${arrIN[0]}:"
+	echo "	jmp ${arrIN[1]}"
+	echo
+done < "$1"
+) > "${1%.lst}.asm"
+
diff --git a/tools/generrnomap b/tools/generrnomap
new file mode 100755
index 000000000..f191ea67b
--- /dev/null
+++ b/tools/generrnomap
@@ -0,0 +1,6 @@
+#!/bin/sh
+
+awk '/#define DARWIN_([A-Z]+) ([0-9]+)/ { printf("darwin_to_linux[%s] = %s;\n", $2, substr($2, 8)); }' < "$1" > "darwin_to_linux.map"
+
+awk '/#define DARWIN_([A-Z]+) ([0-9]+)/ { printf("linux_to_darwin[%s] = %s;\n", substr($2, 8), $2); }' < "$1" > "linux_to_darwin.map"
+