【Tsan】How Tsan shadow memory mapping is chosen ?

[yinchuang-code]

/*
C/C++ on linux/aarch64 (39-bit VMA)
0000 0010 00 - 0100 0000 00: main binary // ~4G
0100 0000 00 - 0400 0000 00: -
0400 0000 00 - 1000 0000 00: shadow memory
2000 0000 00 - 3100 0000 00: -
3100 0000 00 - 3400 0000 00: metainfo
3400 0000 00 - 5500 0000 00: -
5500 0000 00 - 5600 0000 00: main binary (PIE) // 4G
5600 0000 00 - 7c00 0000 00: -
7c00 0000 00 - 7d00 0000 00: heap  // 4G
7d00 0000 00 - 7fff ffff ff: modules and main thread stack  // 8GB
*/
struct MappingAarch64_39 {
  static const uptr kLoAppMemBeg   = 0x0000001000ull;
  static const uptr kLoAppMemEnd   = 0x0100000000ull;
  static const uptr kShadowBeg = 0x0400000000ull;
  static const uptr kShadowEnd = 0x1000000000ull;
  static const uptr kMetaShadowBeg = 0x3100000000ull;
  static const uptr kMetaShadowEnd = 0x3400000000ull;
  static const uptr kMidAppMemBeg  = 0x5500000000ull;
  static const uptr kMidAppMemEnd = 0x5600000000ull;
  static const uptr kHeapMemBeg    = 0x7c00000000ull;
  static const uptr kHeapMemEnd    = 0x7d00000000ull;
  static const uptr kHiAppMemBeg   = 0x7e00000000ull;
  static const uptr kHiAppMemEnd   = 0x7fffffffffull;
  static const uptr kShadowMsk = 0x7800000000ull;
  static const uptr kShadowXor = 0x0200000000ull;
  static const uptr kShadowAdd = 0x0000000000ull;
  static const uptr kVdsoBeg       = 0x7f00000000ull;
};```

1、The memory available to the user is only “8G”？ except main binary
2、Why is it not consistent with asan’s shadow?