lix/boehmgc-coroutine-sp-fallback.diff

diff --git a/pthread_stop_world.c b/pthread_stop_world.c
index 2b45489..0e6d8ef 100644
--- a/pthread_stop_world.c
+++ b/pthread_stop_world.c
@@ -776,6 +776,8 @@ STATIC void GC_restart_handler(int sig)
 /* world is stopped.  Should not fail if it isn't.                      */
 GC_INNER void GC_push_all_stacks(void)
 {
+    size_t stack_limit;
+    pthread_attr_t pattr;
     GC_bool found_me = FALSE;
     size_t nthreads = 0;
     int i;
@@ -868,6 +870,40 @@ GC_INNER void GC_push_all_stacks(void)
             hi = p->altstack + p->altstack_size;
 #         endif
           /* FIXME: Need to scan the normal stack too, but how ? */
+        } else {
+          #ifdef HAVE_PTHREAD_ATTR_GET_NP
+          if (pthread_attr_init(&pattr) != 0) {
+            ABORT("GC_push_all_stacks: pthread_attr_init failed!");
+          }
+          if (pthread_attr_get_np(p->id, &pattr) != 0) {
+            ABORT("GC_push_all_stacks: pthread_attr_get_np failed!");
+          }
+          #else
+          if (pthread_getattr_np(p->id, &pattr)) {
+            ABORT("GC_push_all_stacks: pthread_getattr_np failed!");
+          }
+          #endif
+          if (pthread_attr_getstacksize(&pattr, &stack_limit)) {
+            ABORT("GC_push_all_stacks: pthread_attr_getstacksize failed!");
+          }
+          if (pthread_attr_destroy(&pattr)) {
+            ABORT("GC_push_all_stacks: pthread_attr_destroy failed!");
+          }
+          // When a thread goes into a coroutine, we lose its original sp until
+          // control flow returns to the thread.
+          // While in the coroutine, the sp points outside the thread stack,
+          // so we can detect this and push the entire thread stack instead,
+          // as an approximation.
+          // We assume that the coroutine has similarly added its entire stack.
+          // This could be made accurate by cooperating with the application
+          // via new functions and/or callbacks.
+          #ifndef STACK_GROWS_UP
+            if (lo >= hi || lo < hi - stack_limit) { // sp outside stack
+              lo = hi - stack_limit;
+            }
+          #else
+          #error "STACK_GROWS_UP not supported in boost_coroutine2 (as of june 2021), so we don't support it in Nix."
+          #endif
         }
 #       ifdef STACKPTR_CORRECTOR_AVAILABLE
           if (GC_sp_corrector != 0)