[asan] For iOS/AArch64, if the dynamic shadow doesn't fit, restrict the VM space

On iOS/AArch64, the address space is very limited and has a dynamic maximum address based on the configuration of the device. We're already using a dynamic shadow, and we find a large-enough "gap" in the VM where we place the shadow memory. In some cases and some device configuration, we might not be able to find a large-enough gap: E.g. if the main executable is linked against a large number of libraries that are not part of the system, these libraries can fragment the address space, and this happens before ASan starts initializing.

This patch has a solution, where we have a "backup plan" when we cannot find a large-enough gap: We will restrict the address space (via MmapFixedNoAccess) to a limit, for which the shadow limit will fit.

Differential Revision: https://reviews.llvm.org/D35098



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@307865 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/asan/asan_win.cc b/lib/asan/asan_win.cc
index 26db32465..8a839d913 100644
--- a/lib/asan/asan_win.cc
+++ b/lib/asan/asan_win.cc
@@ -217,6 +217,18 @@ void *AsanDoesNotSupportStaticLinkage() {
   return 0;
 }
 
+uptr FindDynamicShadowStart() {
+  uptr granularity = GetMmapGranularity();
+  uptr alignment = 8 * granularity;
+  uptr left_padding = granularity;
+  uptr space_size = kHighShadowEnd + left_padding;
+  uptr shadow_start =
+      FindAvailableMemoryRange(space_size, alignment, granularity, nullptr);
+  CHECK_NE((uptr)0, shadow_start);
+  CHECK(IsAligned(shadow_start, alignment));
+  return shadow_start;
+}
+
 void AsanCheckDynamicRTPrereqs() {}
 
 void AsanCheckIncompatibleRT() {}