[TSan][MIPS] Expand sanitizer memory space to lower addresses

MemToShadowImpl() maps lower addresses to a memory space out of sanitizers
range. The simplest example is address 0 which is mapped to 0x2000000000

static const uptr kShadowBeg     = 0x2400000000ull;

but accessing the address during tsan execution will lead to a segmentation
fault.

This patch expands the range used by the sanitizer and ensures that 1/8 of
the maximum valid address in the virtual address spaces is used for shadow
memory.

Patch by Milos Stojanovic.

Differential Revision: https://reviews.llvm.org/D41777

llvm-svn: 323013

compiler-rt/lib/tsan/rtl/tsan_platform.h

@@ -79,25 +79,27 @@ struct Mapping {
 #define TSAN_MID_APP_RANGE 1
 #elif defined(__mips64)
 /*
-C/C++ on linux/mips64
-0100 0000 00 - 0200 0000 00: main binary
-0200 0000 00 - 1400 0000 00: -
-1400 0000 00 - 2400 0000 00: shadow
-2400 0000 00 - 3000 0000 00: -
-3000 0000 00 - 4000 0000 00: metainfo (memory blocks and sync objects)
-4000 0000 00 - 6000 0000 00: -
-6000 0000 00 - 6200 0000 00: traces
-6200 0000 00 - fe00 0000 00: -
-fe00 0000 00 - ff00 0000 00: heap
-ff00 0000 00 - ff80 0000 00: -
-ff80 0000 00 - ffff ffff ff: modules and main thread stack
+C/C++ on linux/mips64 (40-bit VMA)
+0000 0000 00 - 0100 0000 00: -                                           (4 GB)
+0100 0000 00 - 0200 0000 00: main binary                                 (4 GB)
+0200 0000 00 - 2000 0000 00: -                                         (120 GB)
+2000 0000 00 - 4000 0000 00: shadow                                    (128 GB)
+4000 0000 00 - 5000 0000 00: metainfo (memory blocks and sync objects)  (64 GB)
+5000 0000 00 - aa00 0000 00: -                                         (360 GB)
+aa00 0000 00 - ab00 0000 00: main binary (PIE)                           (4 GB)
+ab00 0000 00 - b000 0000 00: -                                          (20 GB)
+b000 0000 00 - b200 0000 00: traces                                      (8 GB)
+b200 0000 00 - fe00 0000 00: -                                         (304 GB)
+fe00 0000 00 - ff00 0000 00: heap                                        (4 GB)
+ff00 0000 00 - ff80 0000 00: -                                           (2 GB)
+ff80 0000 00 - ffff ffff ff: modules and main thread stack              (<2 GB)
 */
 struct Mapping {
   static const uptr kMetaShadowBeg = 0x4000000000ull;
   static const uptr kMetaShadowEnd = 0x5000000000ull;
   static const uptr kTraceMemBeg   = 0xb000000000ull;
   static const uptr kTraceMemEnd   = 0xb200000000ull;
-  static const uptr kShadowBeg     = 0x2400000000ull;
+  static const uptr kShadowBeg     = 0x2000000000ull;
   static const uptr kShadowEnd     = 0x4000000000ull;
   static const uptr kHeapMemBeg    = 0xfe00000000ull;
   static const uptr kHeapMemEnd    = 0xff00000000ull;