[Sanitizers] Call NanoTime() conditionally.

Summary:
Call NanoTime() in primary 64 bit allocator only when necessary,
otherwise the unwarranted syscall causes problems in sandbox environments.
ReleaseToOSIntervalMs() conditional allows them to turn the feature off
with allocator_release_to_os_interval_ms=-1 flag.

Reviewers: eugenis

Subscribers: kubamracek, llvm-commits

Differential Revision: https://reviews.llvm.org/D39624

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@317386 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 4 insertions, 1 deletions

diff --git a/lib/sanitizer_common/sanitizer_allocator_primary64.h b/lib/sanitizer_common/sanitizer_allocator_primary64.h
index b22f3aba9..630ae358e 100644
--- a/lib/sanitizer_common/sanitizer_allocator_primary64.h
+++ b/lib/sanitizer_common/sanitizer_allocator_primary64.h
@@ -677,7 +677,10 @@ class SizeClassAllocator64 {
         // preventing just allocated memory from being released sooner than
         // necessary and also preventing extraneous ReleaseMemoryPagesToOS calls
         // for short lived processes.
-        region->rtoi.last_release_at_ns = NanoTime();
+        // Do it only when the feature is turned on, to avoid a potentially
+        // extraneous syscall.
+        if (ReleaseToOSIntervalMs() >= 0)
+          region->rtoi.last_release_at_ns = NanoTime();
       }
       // Do the mmap for the user memory.
       uptr map_size = kUserMapSize;