From cb5da39f20a17bd73e791dca1e7e1832f0adbc53 Mon Sep 17 00:00:00 2001
From: Samuel Williams <samuel.williams@oriontransfer.co.nz>
Date: Wed, 19 Jun 2019 18:47:15 +1200
Subject: [PATCH] Use shared implementation of `rb_ec_initialize_vm_stack`.

---
 cont.c    | 14 +-------------
 thread.c  | 11 +----------
 vm.c      | 28 +++++++++++++++++-----------
 vm_core.h |  7 +++++++
 4 files changed, 26 insertions(+), 34 deletions(-)

diff --git a/cont.c b/cont.c
index e3db1b32d2..accf93aba0 100644
--- a/cont.c
+++ b/cont.c
@@ -1530,19 +1530,7 @@ fiber_init(VALUE fibval, VALUE proc)
         vm_stack = ruby_xmalloc(fib_stack_bytes);
     }
     cont->free_vm_stack = 1;
-    rb_ec_set_vm_stack(sec, vm_stack, fib_stack_bytes / sizeof(VALUE));
-    sec->cfp = (void *)(sec->vm_stack + sec->vm_stack_size);
-
-    rb_vm_push_frame(sec,
-		     NULL,
-		     VM_FRAME_MAGIC_DUMMY | VM_ENV_FLAG_LOCAL | VM_FRAME_FLAG_FINISH | VM_FRAME_FLAG_CFRAME,
-		     Qnil, /* self */
-		     VM_BLOCK_HANDLER_NONE,
-		     0, /* specval */
-		     NULL, /* pc */
-		     sec->vm_stack, /* sp */
-		     0, /* local_size */
-		     0);
+    rb_ec_initialize_vm_stack(sec, vm_stack, fib_stack_bytes / sizeof(VALUE));
 
     sec->tag = NULL;
     sec->local_storage = NULL;
diff --git a/thread.c b/thread.c
index cf418da0e4..df6ca01c9d 100644
--- a/thread.c
+++ b/thread.c
@@ -728,16 +728,7 @@ thread_start_func_2(rb_thread_t *th, VALUE *stack_start, VALUE *register_stack_s
     }
 
     vm_stack = alloca(size * sizeof(VALUE));
-    rb_ec_set_vm_stack(th->ec, vm_stack, size);
-    th->ec->cfp = (void *)(th->ec->vm_stack + th->ec->vm_stack_size);
-
-    rb_vm_push_frame(th->ec,
-        0 /* dummy iseq */,
-        VM_FRAME_MAGIC_DUMMY | VM_ENV_FLAG_LOCAL | VM_FRAME_FLAG_FINISH | VM_FRAME_FLAG_CFRAME /* dummy frame */,
-        Qnil /* dummy self */, VM_BLOCK_HANDLER_NONE /* dummy block ptr */,
-        0 /* dummy cref/me */,
-        0 /* dummy pc */, th->ec->vm_stack, 0, 0
-    );
+    rb_ec_initialize_vm_stack(th->ec, vm_stack, size);
 
     ruby_thread_set_native(th);
 
diff --git a/vm.c b/vm.c
index 4b4b037b4f..439464a42f 100644
--- a/vm.c
+++ b/vm.c
@@ -2685,6 +2685,22 @@ thread_alloc(VALUE klass)
     return obj;
 }
 
+void
+rb_ec_initialize_vm_stack(rb_execution_context_t *ec, VALUE *stack, size_t size)
+{
+  rb_ec_set_vm_stack(ec, stack, size);
+
+  ec->cfp = (void *)(ec->vm_stack + ec->vm_stack_size);
+
+  rb_vm_push_frame(ec,
+      NULL /* dummy iseq */,
+      VM_FRAME_MAGIC_DUMMY | VM_ENV_FLAG_LOCAL | VM_FRAME_FLAG_FINISH | VM_FRAME_FLAG_CFRAME /* dummy frame */,
+      Qnil /* dummy self */, VM_BLOCK_HANDLER_NONE /* dummy block ptr */,
+      0 /* dummy cref/me */,
+      0 /* dummy pc */, ec->vm_stack, 0, 0
+  );
+}
+
 static void
 th_init(rb_thread_t *th, VALUE self)
 {
@@ -2693,17 +2709,7 @@ th_init(rb_thread_t *th, VALUE self)
 
     if (self == 0) {
         size_t size = th->vm->default_params.thread_vm_stack_size / sizeof(VALUE);
-        rb_ec_set_vm_stack(th->ec, ALLOC_N(VALUE, size), size);
-
-        th->ec->cfp = (void *)(th->ec->vm_stack + th->ec->vm_stack_size);
-
-        rb_vm_push_frame(th->ec,
-            0 /* dummy iseq */,
-            VM_FRAME_MAGIC_DUMMY | VM_ENV_FLAG_LOCAL | VM_FRAME_FLAG_FINISH | VM_FRAME_FLAG_CFRAME /* dummy frame */,
-            Qnil /* dummy self */, VM_BLOCK_HANDLER_NONE /* dummy block ptr */,
-            0 /* dummy cref/me */,
-            0 /* dummy pc */, th->ec->vm_stack, 0, 0
-        );
+        rb_ec_initialize_vm_stack(th->ec, ALLOC_N(VALUE, size), size);
     } else {
       VM_ASSERT(th->ec->cfp == NULL);
       VM_ASSERT(th->ec->vm_stack == NULL);
diff --git a/vm_core.h b/vm_core.h
index a0f9388df7..7860c2d505 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -903,8 +903,15 @@ typedef struct rb_execution_context_struct {
     } machine;
 } rb_execution_context_t;
 
+// Set the vm_stack pointer in the execution context.
 void rb_ec_set_vm_stack(rb_execution_context_t *ec, VALUE *stack, size_t size);
 
+// Initialize the vm_stack pointer in the execution context and push the initial stack frame.
+// @param ec the execution context to update.
+// @param stack a pointer to the stack to use.
+// @param size the size of the stack, as in `VALUE stack[size]`.
+void rb_ec_initialize_vm_stack(rb_execution_context_t *ec, VALUE *stack, size_t size);
+
 typedef struct rb_thread_struct {
     struct list_node vmlt_node;
     VALUE self;