Check ASAN fake stacks when marking non-current threads

Currently, we check the values on the machine stack & register state to
see if they're actually a pointer to an ASAN fake stack, and mark the
values on the fake stack too if required. However, we are only doing
that for the _current_ thread (the one actually running the GC), not for
any other thread in the program.

Make rb_gc_mark_machine_context (which is called for marking non-current
threads) perform the same ASAN fake stack handling that
mark_current_machine_context performs.

[Bug #20310]

3 files changed, 18 insertions, 9 deletions

diff --git a/gc.c b/gc.c
index 07c0735a44..282e9df0cf 100644
--- a/gc.c
+++ b/gc.c
@@ -949,7 +949,7 @@ typedef struct rb_objspace {
     rb_postponed_job_handle_t finalize_deferred_pjob;
 
 #ifdef RUBY_ASAN_ENABLED
-    rb_execution_context_t *marking_machine_context_ec;
+    const rb_execution_context_t *marking_machine_context_ec;
 #endif
 
 } rb_objspace_t;
@@ -6406,7 +6406,7 @@ gc_mark_machine_stack_location_maybe(rb_objspace_t *objspace, VALUE obj)
     gc_mark_maybe(objspace, obj);
 
 #ifdef RUBY_ASAN_ENABLED
-    rb_execution_context_t *ec = objspace->marking_machine_context_ec;
+    const rb_execution_context_t *ec = objspace->marking_machine_context_ec;
     void *fake_frame_start;
     void *fake_frame_end;
     bool is_fake_frame = asan_get_fake_stack_extents(
@@ -6495,13 +6495,25 @@ mark_current_machine_context(rb_objspace_t *objspace, rb_execution_context_t *ec
 #endif
 
 void
-rb_gc_mark_machine_stack(const rb_execution_context_t *ec)
+rb_gc_mark_machine_context(const rb_execution_context_t *ec)
 {
+    rb_objspace_t *objspace = &rb_objspace;
+#ifdef RUBY_ASAN_ENABLED
+    objspace->marking_machine_context_ec = ec;
+#endif
+
     VALUE *stack_start, *stack_end;
+
     GET_STACK_BOUNDS(stack_start, stack_end, 0);
     RUBY_DEBUG_LOG("ec->th:%u stack_start:%p stack_end:%p", rb_ec_thread_ptr(ec)->serial, stack_start, stack_end);
 
-    rb_gc_mark_locations(stack_start, stack_end);
+    each_stack_location(objspace, ec, stack_start, stack_end, gc_mark_machine_stack_location_maybe);
+    int num_regs = sizeof(ec->machine.regs)/(sizeof(VALUE));
+    each_location(objspace, (VALUE*)&ec->machine.regs, num_regs, gc_mark_machine_stack_location_maybe);
+
+#ifdef RUBY_ASAN_ENABLED
+    objspace->marking_machine_context_ec = NULL;
+#endif
 }
 
 static void
diff --git a/vm.c b/vm.c
index 82bf1ac658..882514db41 100644
--- a/vm.c
+++ b/vm.c
@@ -3399,10 +3399,7 @@ rb_execution_context_mark(const rb_execution_context_t *ec)
     if (ec->machine.stack_start && ec->machine.stack_end &&
         ec != GET_EC() /* marked for current ec at the first stage of marking */
         ) {
-        rb_gc_mark_machine_stack(ec);
-        rb_gc_mark_locations((VALUE *)&ec->machine.regs,
-                             (VALUE *)(&ec->machine.regs) +
-                             sizeof(ec->machine.regs) / (sizeof(VALUE)));
+        rb_gc_mark_machine_context(ec);
     }
 
     rb_gc_mark(ec->errinfo);
diff --git a/vm_core.h b/vm_core.h
index 805df18616..2a9d5f906f 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -1874,7 +1874,7 @@ void rb_vm_register_special_exception_str(enum ruby_special_exceptions sp, VALUE
 #define rb_vm_register_special_exception(sp, e, m) \
     rb_vm_register_special_exception_str(sp, e, rb_usascii_str_new_static((m), (long)rb_strlen_lit(m)))
 
-void rb_gc_mark_machine_stack(const rb_execution_context_t *ec);
+void rb_gc_mark_machine_context(const rb_execution_context_t *ec);
 
 void rb_vm_rewrite_cref(rb_cref_t *node, VALUE old_klass, VALUE new_klass, rb_cref_t **new_cref_ptr);