Pass down "stack start" variables from closer to the top of the stack

The implementation of `native_thread_init_stack` for the various
threading models can use the address of a local variable as part of the
calculation of the machine stack extents:

* pthreads uses it as a lower-bound on the start of the stack, because
  glibc (and maybe other libcs) can store its own data on the stack
  before calling into user code on thread creation.
* win32 uses it as an argument to VirtualQuery, which gets the extent of
  the memory mapping which contains the variable

However, the local being used for this is actually allocated _inside_
the `native_thread_init_stack` frame; that means the caller might
allocate a VALUE on the stack that actually lies outside the bounds
stored in machine.stack_{start,end}.

A local variable from one level above the topmost frame that stores
VALUEs on the stack must be drilled down into the call to
`native_thread_init_stack` to be used in the calculation. This probably
doesn't _really_ matter for the win32 case (they'll be in the same
memory mapping so VirtualQuery should return the same thing), but
definitely could matter for the pthreads case.

[Bug #20001]

1 files changed, 2 insertions, 2 deletions

diff --git a/thread.c b/thread.c
index 070d1bbdfa..e7a9d7cd9b 100644
--- a/thread.c
+++ b/thread.c
@@ -522,9 +522,9 @@ static VALUE rb_threadptr_raise(rb_thread_t *, int, VALUE *);
 static VALUE rb_thread_to_s(VALUE thread);
 
 void
-ruby_thread_init_stack(rb_thread_t *th)
+ruby_thread_init_stack(rb_thread_t *th, void *local_in_parent_frame)
 {
-    native_thread_init_stack(th);
+    native_thread_init_stack(th, local_in_parent_frame);
 }
 
 const VALUE *