[sanitizer] Fix aarch64 sanitizer build with recent glibc

[Jakub Jelinek]

Hi!

glibc recently changed ABI on aarch64-linux:
https://sourceware.org/git/?p=glibc.git;a=commit;h=5c40c3bab2fddaca8cfe12d75944d1fef8adf1a4
Instead of having unsigned short mode; unsigned short __pad1; it now has
unsigned int mode; field in ipc_perm structure.

This patch allows to build against the recent glibc and disables the
ipc_perm.mode verification for older versions of glibc.

I think it shouldn't be a big deal even for older glibcs, I couldn't find
any place which would actually care about the exact mode field, rather than
the whole structure, appart from the CHECK_SIZE_AND_OFFSET macro.

--- compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.h.jj	2014-10-14 15:11:22.170590985 +0200
+++ compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.h	2015-01-20 18:53:20.969780785 +0100
@@ -169,7 +169,7 @@ namespace __sanitizer {
     unsigned __seq;
     u64 __unused1;
     u64 __unused2;
-#elif defined(__mips__)
+#elif defined(__mips__) || defined(__aarch64__)
     unsigned int mode;
     unsigned short __seq;
     unsigned short __pad1;
--- compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cc.jj	2014-12-15 19:50:53.597624368 +0100
+++ compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cc	2015-01-20 18:53:21.007780141 +0100
@@ -1061,7 +1061,13 @@ CHECK_SIZE_AND_OFFSET(ipc_perm, uid);
 CHECK_SIZE_AND_OFFSET(ipc_perm, gid);
 CHECK_SIZE_AND_OFFSET(ipc_perm, cuid);
 CHECK_SIZE_AND_OFFSET(ipc_perm, cgid);
+#ifndef __GLIBC_PREREQ
+#define __GLIBC_PREREQ(x, y) 0
+#endif
+#if !defined(__aarch64__) || !SANITIZER_LINUX || __GLIBC_PREREQ (2, 21)
+/* On aarch64 glibc 2.20 and earlier provided incorrect mode field.  */
 CHECK_SIZE_AND_OFFSET(ipc_perm, mode);
+#endif
 
 CHECK_TYPE_SIZE(shmid_ds);
 CHECK_SIZE_AND_OFFSET(shmid_ds, shm_perm);


	Jakub