[scudo] Add Android support

Summary:
This change adds Android support to the allocator (but doesn't yet enable it in
the cmake config), and should be the last fragment of the rewritten change
D31947.

Android has more memory constraints than other platforms, so the idea of a
unique context per thread would not have worked. The alternative chosen is to
allocate a set of contexts based on the number of cores on the machine, and
share those contexts within the threads. Contexts can be dynamically reassigned
to threads to prevent contention, based on a scheme suggested by @dvyuokv in
the initial review.

Additionally, given that Android doesn't support ELF TLS (only emutls for now),
we use the TSan TLS slot to make things faster: Scudo is mutually exclusive
with other sanitizers so this shouldn't cause any problem.

An additional change made here, is replacing `thread_local` by `THREADLOCAL`
and using the initial-exec thread model in the non-Android version to prevent
extraneous weak definition and checks on the relevant variables.

Reviewers: kcc, dvyukov, alekseyshl

Reviewed By: alekseyshl

Subscribers: srhines, mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D32649

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@302300 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/scudo/scudo_allocator.h b/lib/scudo/scudo_allocator.h
index 2cac2de71..f159deffb 100644
--- a/lib/scudo/scudo_allocator.h
+++ b/lib/scudo/scudo_allocator.h
@@ -72,7 +72,13 @@ const uptr AlignedChunkHeaderSize =
 
 #if SANITIZER_CAN_USE_ALLOCATOR64
 const uptr AllocatorSpace = ~0ULL;
-const uptr AllocatorSize = 0x40000000000ULL;  // 4TB.
+# if defined(__aarch64__) && SANITIZER_ANDROID
+const uptr AllocatorSize = 0x4000000000ULL;  // 256G.
+# elif defined(__aarch64__)
+const uptr AllocatorSize = 0x10000000000ULL;  // 1T.
+# else
+const uptr AllocatorSize = 0x40000000000ULL;  // 4T.
+# endif
 typedef DefaultSizeClassMap SizeClassMap;
 struct AP {
   static const uptr kSpaceBeg = AllocatorSpace;