3 files changed, 33 insertions, 6 deletions
diff --git a/internal/sanitizers.h b/internal/sanitizers.h
index 7b7d166c74..6b2a131925 100644
--- a/internal/sanitizers.h
+++ b/internal/sanitizers.h
@@ -64,6 +64,8 @@
 # define __asan_poison_memory_region(x, y)
 # define __asan_unpoison_memory_region(x, y)
 # define __asan_region_is_poisoned(x, y) 0
+# define __asan_get_current_fake_stack() NULL
+# define __asan_addr_is_in_fake_stack(fake_stack, slot, start, end) NULL
 #endif
 
 #if !__has_feature(memory_sanitizer)
@@ -183,4 +185,28 @@ asan_unpoison_object(VALUE obj, bool newobj_p)
     asan_unpoison_memory_region(ptr, SIZEOF_VALUE, newobj_p);
 }
 
+
+/*!
+ * Checks if the given pointer is on an ASAN fake stack. If so, it returns the
+ * address this variable has on the real frame; if not, it returns the origin
+ * address unmodified.
+ *
+ * n.b. - _dereferencing_ the returned address is meaningless and should not
+ * be done; even though ASAN reserves space for the variable in both the real and
+ * fake stacks, the _value_ of that variable is only in the fake stack.
+ *
+ * n.b. - this only works for addresses passed in from local variables on the same
+ * thread, because the ASAN fake stacks are threadlocal.
+ *
+ * \param[in] slot  the address of some local variable
+ * \retval          a pointer to something from that frame on the _real_ machine stack
+ */
+static inline void *
+asan_get_real_stack_addr(void* slot)
+{
+    VALUE *addr;
+    addr = __asan_addr_is_in_fake_stack(__asan_get_current_fake_stack(), slot, NULL, NULL);
+    return addr ? addr : slot;
+}
+
 #endif /* INTERNAL_SANITIZERS_H */
diff --git a/thread_pthread.c b/thread_pthread.c
index a6a6c9d127..af50d50699 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -12,6 +12,7 @@
 #ifdef THREAD_SYSTEM_DEPENDENT_IMPLEMENTATION
 
 #include "internal/gc.h"
+#include "internal/sanitizers.h"
 #include "rjit.h"
 
 #ifdef HAVE_SYS_RESOURCE_H
@@ -1967,6 +1968,7 @@ void
 ruby_init_stack(volatile void *addr)
 {
     native_main_thread.id = pthread_self();
+    addr = asan_get_real_stack_addr((void *)addr);
 
 #if MAINSTACKADDR_AVAILABLE
     if (native_main_thread.stack_maxsize) return;
@@ -2065,7 +2067,7 @@ native_thread_init_stack(rb_thread_t *th, void *local_in_parent_frame)
 
             if (get_stack(&start, &size) == 0) {
                 uintptr_t diff = (uintptr_t)start - (uintptr_t)local_in_parent_frame;
-                th->ec->machine.stack_start = (uintptr_t)local_in_parent_frame;
+                th->ec->machine.stack_start = asan_get_real_stack_addr(local_in_parent_frame);
                 th->ec->machine.stack_maxsize = size - diff;
             }
         }
@@ -2192,12 +2194,10 @@ call_thread_start_func_2(rb_thread_t *th)
        on a new thread, and replacing that data on fiber-switch would break it (see
        bug #13887) */
     VALUE stack_start = 0;
-    VALUE *stack_start_addr = &stack_start;
+    VALUE *stack_start_addr = asan_get_real_stack_addr(&stack_start);
+
     native_thread_init_stack(th, stack_start_addr);
     thread_start_func_2(th, th->ec->machine.stack_start);
-
-    /* Ensure that stack_start really was spilled to the stack */
-    RB_GC_GUARD(stack_start)
 }
 
 static void *
diff --git a/thread_win32.c b/thread_win32.c
index e92472cea9..c294542003 100644
--- a/thread_win32.c
+++ b/thread_win32.c
@@ -11,6 +11,7 @@
 
 #ifdef THREAD_SYSTEM_DEPENDENT_IMPLEMENTATION
 
+#include "internal/sanitizers.h"
 #include <process.h>
 
 #define TIME_QUANTUM_USEC (10 * 1000)
@@ -596,7 +597,7 @@ COMPILER_WARNING_IGNORED(-Wmaybe-uninitialized)
 static inline SIZE_T
 query_memory_basic_info(PMEMORY_BASIC_INFORMATION mi, void *local_in_parent_frame)
 {
-    return VirtualQuery(local_in_parent_frame, mi, sizeof(*mi));
+    return VirtualQuery(asan_get_real_stack_addr(local_in_parent_frame), mi, sizeof(*mi));
 }
 COMPILER_WARNING_POP