fibers getStackPointer

Summary: exposing fiber stack pointers so that we can walk the traces and print them in the next diff

Reviewed By: yfeldblum

Differential Revision: D76646227

fbshipit-source-id: c3f7fc1b422231d96be509e4c6d212b7368c2d82

Author: Mateusz Dziekan

third-party/folly/src/folly/fibers/BoostContextCompatibility.h

@@ -62,6 +62,13 @@ class FiberImpl {
     DCHECK_EQ(this, reinterpret_cast<FiberImpl*>(context));
   }
 
+  void* getStackPointer() const {
+    if (kIsArchAmd64 && kIsLinux) {
+      return reinterpret_cast<void**>(fiberContext_)[6];
+    }
+    return nullptr;
+  }
+
  private:
   static void fiberFunc(boost::context::detail::transfer_t transfer) {
     auto fiberImpl = reinterpret_cast<FiberImpl*>(transfer.data);

third-party/folly/src/folly/fibers/Fiber.h

@@ -76,7 +76,7 @@ class Fiber {
   /**
    * Retrieve this fiber's base stack and stack size.
    *
-   * @return This fiber's stack pointer and stack size.
+   * @return This fiber's base stack pointer and stack size.
    */
   std::pair<void*, size_t> getStack() const {
     return {fiberStackLimit_, fiberStackSize_};
@@ -99,6 +99,13 @@ class Fiber {
 
   State getState() const { return state_; }
 
+  /**
+   * Retrieve this fiber's stack pointer. This is only meant for debugging.
+   *
+   * @return This fiber's current stack pointer.
+   */
+  void* getStackPointer() const { return fiberImpl_.getStackPointer(); }
+
  private:
   State state_{INVALID}; /**< current Fiber state */