[compiler-rt] r285454 - tsan: round Go shadow to page boundary

[Dmitry Vyukov via llvm-commits]

Author: dvyukov
Date: Fri Oct 28 16:24:29 2016
New Revision: 285454

URL: http://llvm.org/viewvc/llvm-project?rev=285454&view=rev
Log:
tsan: round Go shadow to page boundary

There is a corner case reported in Go issue tracker:
https://github.com/golang/go/issues/17065
On darwin data/bss segments may not be aligned to page bounary
and mmap seems to be behaving differently than on linux
(shrinks instead of enlarge unaligned regions).

Explicitly round shadow to page bounary before mapping
to avoid any such problems.


Modified:
    compiler-rt/trunk/lib/tsan/rtl/tsan_rtl.cc

Modified: compiler-rt/trunk/lib/tsan/rtl/tsan_rtl.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/tsan/rtl/tsan_rtl.cc?rev=285454&r1=285453&r2=285454&view=diff
==============================================================================
--- compiler-rt/trunk/lib/tsan/rtl/tsan_rtl.cc (original)
+++ compiler-rt/trunk/lib/tsan/rtl/tsan_rtl.cc Fri Oct 28 16:24:29 2016
@@ -242,7 +242,10 @@ void MapShadow(uptr addr, uptr size) {
   // Global data is not 64K aligned, but there are no adjacent mappings,
   // so we can get away with unaligned mapping.
   // CHECK_EQ(addr, addr & ~((64 << 10) - 1));  // windows wants 64K alignment
-  MmapFixedNoReserve(MemToShadow(addr), size * kShadowMultiplier, "shadow");
+  const uptr kPageSize = GetPageSizeCached();
+  uptr shadow_begin = RoundDownTo((uptr)MemToShadow(addr), kPageSize);
+  uptr shadow_end = RoundUpTo((uptr)MemToShadow(addr + size), kPageSize);
+  MmapFixedNoReserve(shadow_begin, shadow_end - shadow_begin, "shadow");
 
   // Meta shadow is 2:1, so tread carefully.
   static bool data_mapped = false;