diff --git a/compiler-rt/lib/lsan/lsan_common.cpp b/compiler-rt/lib/lsan/lsan_common.cpp
--- a/compiler-rt/lib/lsan/lsan_common.cpp
+++ b/compiler-rt/lib/lsan/lsan_common.cpp
@@ -218,10 +218,7 @@
 // Scans thread data (stacks and TLS) for heap pointers.
 static void ProcessThreads(SuspendedThreadsList const &suspended_threads,
                            Frontier *frontier) {
-  InternalMmapVector<uptr> registers(suspended_threads.RegisterCount());
-  uptr registers_begin = reinterpret_cast<uptr>(registers.data());
-  uptr registers_end =
-      reinterpret_cast<uptr>(registers.data() + registers.size());
+  InternalMmapVector<uptr> registers;
   for (uptr i = 0; i < suspended_threads.ThreadCount(); i++) {
     tid_t os_id = static_cast<tid_t>(suspended_threads.GetThreadID(i));
     LOG_THREADS("Processing thread %d.\n", os_id);
@@ -238,7 +235,7 @@
     }
     uptr sp;
     PtraceRegistersStatus have_registers =
-        suspended_threads.GetRegistersAndSP(i, registers.data(), &sp);
+        suspended_threads.GetRegistersAndSP(i, &registers, &sp);
     if (have_registers != REGISTERS_AVAILABLE) {
       Report("Unable to get registers from thread %d.\n", os_id);
       // If unable to get SP, consider the entire stack to be reachable unless
@@ -247,9 +244,13 @@
       sp = stack_begin;
     }
 
-    if (flags()->use_registers && have_registers)
+    if (flags()->use_registers && have_registers) {
+      uptr registers_begin = reinterpret_cast<uptr>(registers.data());
+      uptr registers_end =
+          reinterpret_cast<uptr>(registers.data() + registers.size());
       ScanRangeForPointers(registers_begin, registers_end, frontier,
                            "REGISTERS", kReachable);
+    }
 
     if (flags()->use_stacks) {
       LOG_THREADS("Stack at %p-%p (SP = %p).\n", stack_begin, stack_end, sp);
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld.h b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld.h
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld.h
@@ -32,13 +32,11 @@
 
   // Can't declare pure virtual functions in sanitizer runtimes:
   // __cxa_pure_virtual might be unavailable. Use UNIMPLEMENTED() instead.
-  virtual PtraceRegistersStatus GetRegistersAndSP(uptr index, uptr *buffer,
-                                                  uptr *sp) const {
+  virtual PtraceRegistersStatus GetRegistersAndSP(
+      uptr index, InternalMmapVector<uptr> *buffer, uptr *sp) const {
     UNIMPLEMENTED();
   }
 
-  // The buffer in GetRegistersAndSP should be at least this big.
-  virtual uptr RegisterCount() const { UNIMPLEMENTED(); }
   virtual uptr ThreadCount() const { UNIMPLEMENTED(); }
   virtual tid_t GetThreadID(uptr index) const { UNIMPLEMENTED(); }
 
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
@@ -94,9 +94,9 @@
   bool ContainsTid(tid_t thread_id) const;
   void Append(tid_t tid);
 
-  PtraceRegistersStatus GetRegistersAndSP(uptr index, uptr *buffer,
+  PtraceRegistersStatus GetRegistersAndSP(uptr index,
+                                          InternalMmapVector<uptr> *buffer,
                                           uptr *sp) const override;
-  uptr RegisterCount() const override;
 
  private:
   InternalMmapVector<tid_t> thread_ids_;
@@ -533,7 +533,7 @@
 }
 
 PtraceRegistersStatus SuspendedThreadsListLinux::GetRegistersAndSP(
-    uptr index, uptr *buffer, uptr *sp) const {
+    uptr index, InternalMmapVector<uptr> *buffer, uptr *sp) const {
   pid_t tid = GetThreadID(index);
   regs_struct regs;
   int pterrno;
@@ -559,13 +559,11 @@
   }
 
   *sp = regs.REG_SP;
-  internal_memcpy(buffer, &regs, sizeof(regs));
+  buffer->resize(RoundUpTo(sizeof(regs), sizeof(uptr)) / sizeof(uptr));
+  internal_memcpy(buffer->data(), &regs, sizeof(regs));
   return REGISTERS_AVAILABLE;
 }
 
-uptr SuspendedThreadsListLinux::RegisterCount() const {
-  return sizeof(regs_struct) / sizeof(uptr);
-}
 } // namespace __sanitizer
 
 #endif  // SANITIZER_LINUX && (defined(__x86_64__) || defined(__mips__)
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_mac.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_mac.cpp
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_mac.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_mac.cpp
@@ -37,9 +37,9 @@
   bool ContainsThread(thread_t thread) const;
   void Append(thread_t thread);
 
-  PtraceRegistersStatus GetRegistersAndSP(uptr index, uptr *buffer,
+  PtraceRegistersStatus GetRegistersAndSP(uptr index,
+                                          InternalMmapVector<uptr> *buffer,
                                           uptr *sp) const override;
-  uptr RegisterCount() const override;
 
  private:
   InternalMmapVector<SuspendedThreadInfo> threads_;
@@ -142,7 +142,7 @@
 }
 
 PtraceRegistersStatus SuspendedThreadsListMac::GetRegistersAndSP(
-    uptr index, uptr *buffer, uptr *sp) const {
+    uptr index, InternalMmapVector<uptr> *buffer, uptr *sp) const {
   thread_t thread = GetThread(index);
   regs_struct regs;
   int err;
@@ -159,7 +159,8 @@
                                         : REGISTERS_UNAVAILABLE;
   }
 
-  internal_memcpy(buffer, &regs, sizeof(regs));
+  buffer->resize(RoundUpTo(sizeof(regs), sizeof(uptr)) / sizeof(uptr));
+  internal_memcpy(buffer->data(), &regs, sizeof(regs));
 #if defined(__aarch64__) && defined(arm_thread_state64_get_sp)
   *sp = arm_thread_state64_get_sp(regs);
 #else
@@ -173,9 +174,6 @@
   return REGISTERS_AVAILABLE;
 }
 
-uptr SuspendedThreadsListMac::RegisterCount() const {
-  return MACHINE_THREAD_STATE_COUNT;
-}
 } // namespace __sanitizer
 
 #endif  // SANITIZER_MAC && (defined(__x86_64__) || defined(__aarch64__)) ||
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_netbsd_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_netbsd_libcdep.cpp
--- a/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_netbsd_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_stoptheworld_netbsd_libcdep.cpp
@@ -57,9 +57,9 @@
   bool ContainsTid(tid_t thread_id) const;
   void Append(tid_t tid);
 
-  PtraceRegistersStatus GetRegistersAndSP(uptr index, uptr *buffer,
+  PtraceRegistersStatus GetRegistersAndSP(uptr index,
+                                          InternalMmapVector<uptr> *buffer,
                                           uptr *sp) const;
-  uptr RegisterCount() const;
 
  private:
   InternalMmapVector<tid_t> thread_ids_;
@@ -335,7 +335,7 @@
 }
 
 PtraceRegistersStatus SuspendedThreadsListNetBSD::GetRegistersAndSP(
-    uptr index, uptr *buffer, uptr *sp) const {
+    uptr index, InternalMmapVector<uptr> *buffer, uptr *sp) const {
   lwpid_t tid = GetThreadID(index);
   pid_t ppid = internal_getppid();
   struct reg regs;
@@ -351,14 +351,12 @@
   }
 
   *sp = PTRACE_REG_SP(&regs);
-  internal_memcpy(buffer, &regs, sizeof(regs));
+  buffer->resize(RoundUpTo(sizeof(regs), sizeof(uptr)) / sizeof(uptr));
+  internal_memcpy(buffer->data(), &regs, sizeof(regs));
 
   return REGISTERS_AVAILABLE;
 }
 
-uptr SuspendedThreadsListNetBSD::RegisterCount() const {
-  return sizeof(struct reg) / sizeof(uptr);
-}
 }  // namespace __sanitizer
 
 #endif