release-request-c1e89bbc-a9dd-4c96-8532-caeb99fb86d6-for-git_oc-dr1-release-4229604 snap-temp-L39800000087367876
Change-Id: I1386c9fe515d8106859d5437c14db694b4481345
diff --git a/runtime/thread.cc b/runtime/thread.cc
index 789f571..b3e5221 100644
--- a/runtime/thread.cc
+++ b/runtime/thread.cc
@@ -547,27 +547,47 @@
//
// We map in the stack by reading every page from the stack bottom (highest address)
// to the stack top. (We then madvise this away.) This must be done by reading from the
- // current stack pointer downwards. Any access more than a page below the current SP
- // might cause a segv.
- // TODO: This comment may be out of date. It seems possible to speed this up. As
- // this is normally done once in the zygote on startup, ignore for now.
+ // current stack pointer downwards.
//
- // AddressSanitizer does not like the part of this functions that reads every stack page.
- // Looks a lot like an out-of-bounds access.
+ // Accesses too far below the current machine register corresponding to the stack pointer (e.g.,
+ // ESP on x86[-32], SP on ARM) might cause a SIGSEGV (at least on x86 with newer kernels). We
+ // thus have to move the stack pointer. We do this portably by using a recursive function with a
+ // large stack frame size.
- // (Defensively) first remove the protection on the protected region as will want to read
+ // (Defensively) first remove the protection on the protected region as we'll want to read
// and write it. Ignore errors.
UnprotectStack();
VLOG(threads) << "Need to map in stack for thread at " << std::hex <<
static_cast<void*>(pregion);
- // Read every page from the high address to the low.
- volatile uint8_t dont_optimize_this;
- UNUSED(dont_optimize_this);
- for (uint8_t* p = stack_top; p >= pregion; p -= kPageSize) {
- dont_optimize_this = *p;
- }
+ struct RecurseDownStack {
+ // This function has an intentionally large stack size.
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wframe-larger-than="
+ NO_INLINE
+ static void Touch(uintptr_t target) {
+ volatile size_t zero = 0;
+ // Use a large local volatile array to ensure a large frame size. Do not use anything close
+ // to a full page for ASAN. It would be nice to ensure the frame size is at most a page, but
+ // there is no pragma support for this.
+ // Note: for ASAN we need to shrink the array a bit, as there's other overhead.
+ constexpr size_t kAsanMultiplier =
+#ifdef ADDRESS_SANITIZER
+ 2u;
+#else
+ 1u;
+#endif
+ volatile char space[kPageSize - (kAsanMultiplier * 256)];
+ char sink ATTRIBUTE_UNUSED = space[zero];
+ if (reinterpret_cast<uintptr_t>(space) >= target + kPageSize) {
+ Touch(target);
+ }
+ zero *= 2; // Try to avoid tail recursion.
+ }
+#pragma GCC diagnostic pop
+ };
+ RecurseDownStack::Touch(reinterpret_cast<uintptr_t>(pregion));
VLOG(threads) << "(again) installing stack protected region at " << std::hex <<
static_cast<void*>(pregion) << " to " <<
