rt: Get rid of the rethrow in upcall_fail

Throwing in upcall_fail ends up running lots of code in the red zone. To avoid
it we have the personality function figure out which stack it's on and switch
as needed.

1 files changed, 14 insertions, 7 deletions

diff --git a/src/rt/rust_upcall.cpp b/src/rt/rust_upcall.cpp
index 506441979ca..5febc5098a2 100644
--- a/src/rt/rust_upcall.cpp
+++ b/src/rt/rust_upcall.cpp
@@ -88,12 +88,8 @@ extern "C" CDECL void
 upcall_fail(char const *expr,
             char const *file,
             size_t line) {
-    try {
-        s_fail_args args = {expr,file,line};
-        UPCALL_SWITCH_STACK(&args, upcall_s_fail);
-    } catch (rust_task*) {
-        throw;
-    }
+    s_fail_args args = {expr,file,line};
+    UPCALL_SWITCH_STACK(&args, upcall_s_fail);
 }
 
 /**********************************************************************
@@ -536,7 +532,18 @@ upcall_rust_personality(int version,
     s_rust_personality_args args = {(_Unwind_Reason_Code)0,
                                     version, actions, exception_class,
                                     ue_header, context};
-    UPCALL_SWITCH_STACK(&args, upcall_s_rust_personality);
+    rust_task *task = rust_scheduler::get_task();
+
+    // The personality function is run on the stack of the
+    // last function that threw or landed, which is going
+    // to sometimes be the C stack. If we're on the Rust stack
+    // then switch to the C stack.
+
+    if (task->on_rust_stack()) {
+        UPCALL_SWITCH_STACK(&args, upcall_s_rust_personality);
+    } else {
+        upcall_s_rust_personality(&args);
+    }
     return args.retval;
 }