fixes #7827, bindSym enhancement (#8499)

* bindSym power up, working prototype

* update bindSym doc

* add bindSym test

* fix some typo

* fix bindSym doc

* get rid of specialops field from vm

* add experimental: dynamicBindSym

compiler/vm.nim

@@ -1222,9 +1222,25 @@ proc rawExecute(c: PCtx, start: int, tos: PStackFrame): TFullReg =
           node.typ.callConv == ccClosure and node.sons[0].kind == nkNilLit and
           node.sons[1].kind == nkNilLit))
     of opcNBindSym:
+      # cannot use this simple check
+      # if dynamicBindSym notin c.config.features:
+
+      # bindSym with static input
       decodeBx(rkNode)
       regs[ra].node = copyTree(c.constants.sons[rbx])
       regs[ra].node.flags.incl nfIsRef
+    of opcNDynBindSym:
+      # experimental bindSym
+      let
+        rb = instr.regB
+        rc = instr.regC
+        idx = int(regs[rb+rc-1].intVal)
+        callback = c.callbacks[idx].value
+        args = VmArgs(ra: ra, rb: rb, rc: rc, slots: cast[pointer](regs),
+                currentException: c.currentExceptionB,
+                currentLineInfo: c.debug[pc])
+      callback(args)
+      regs[ra].node.flags.incl nfIsRef
     of opcNChild:
       decodeBC(rkNode)
       let idx = regs[rc].intVal.int
@@ -1773,7 +1789,7 @@ proc getGlobalValue*(c: PCtx; s: PSym): PNode =
 
 include vmops
 
-proc setupGlobalCtx(module: PSym; graph: ModuleGraph) =
+proc setupGlobalCtx*(module: PSym; graph: ModuleGraph) =
   if graph.vm.isNil:
     graph.vm = newCtx(module, graph.cache, graph)
     registerAdditionalOps(PCtx graph.vm)