From 6b4824c2ab04fdd177da88d419fced2efb8dbd1e Mon Sep 17 00:00:00 2001
From: Calvin Rose <calsrose@gmail.com>
Date: Sun, 30 Dec 2018 18:41:44 -0500
Subject: [PATCH] Fix error behavior when calling functions with incorrect
 arities.

---
 src/core/fiber.c  | 34 ++++++++++++++++------------------
 src/core/vm.c     |  4 ++++
 test/suite3.janet |  4 ++++
 3 files changed, 24 insertions(+), 18 deletions(-)

diff --git a/src/core/fiber.c b/src/core/fiber.c
index 0effde74..a4dc7afc 100644
--- a/src/core/fiber.c
+++ b/src/core/fiber.c
@@ -50,8 +50,7 @@ static JanetFiber *make_fiber(int32_t capacity) {
 /* Initialize a new fiber */
 JanetFiber *janet_fiber(JanetFunction *callee, int32_t capacity) {
     JanetFiber *fiber = make_fiber(capacity);
-    if (janet_fiber_funcframe(fiber, callee))
-        janet_fiber_set_status(fiber, JANET_STATUS_ERROR);
+    if (janet_fiber_funcframe(fiber, callee)) return NULL;
     return fiber;
 }
 
@@ -65,8 +64,7 @@ JanetFiber *janet_fiber_n(JanetFunction *callee, int32_t capacity, const Janet *
     }
     memcpy(fiber->data + fiber->stacktop, argv, argn * sizeof(Janet));
     fiber->stacktop = newstacktop;
-    if (janet_fiber_funcframe(fiber, callee))
-        janet_fiber_set_status(fiber, JANET_STATUS_ERROR);
+    if (janet_fiber_funcframe(fiber, callee)) return NULL;
     return fiber;
 }
 
@@ -132,6 +130,13 @@ int janet_fiber_funcframe(JanetFiber *fiber, JanetFunction *func) {
     int32_t nextstacktop = nextframe + func->def->slotcount + JANET_FRAME_SIZE;
     int32_t next_arity = fiber->stacktop - fiber->stackstart;
 
+    /* Check strict arity before messing with state */
+    if (func->def->flags & JANET_FUNCDEF_FLAG_FIXARITY) {
+        if (func->def->arity != next_arity) {
+            return 1;
+        }
+    }
+
     if (fiber->capacity < nextstacktop) {
         janet_fiber_setcapacity(fiber, 2 * nextstacktop);
     }
@@ -163,13 +168,6 @@ int janet_fiber_funcframe(JanetFiber *fiber, JanetFunction *func) {
         }
     }
 
-    /* Check strict arity AFTER getting fiber to valid state. */
-    if (func->def->flags & JANET_FUNCDEF_FLAG_FIXARITY) {
-        if (func->def->arity != next_arity) {
-            return 1;
-        }
-    }
-
     /* Good return */
     return 0;
 }
@@ -198,6 +196,13 @@ int janet_fiber_funcframe_tail(JanetFiber *fiber, JanetFunction *func) {
     int32_t next_arity = fiber->stacktop - fiber->stackstart;
     int32_t stacksize;
 
+    /* Check strict arity before messing with state */
+    if (func->def->flags & JANET_FUNCDEF_FLAG_FIXARITY) {
+        if (func->def->arity != next_arity) {
+            return 1;
+        }
+    }
+
     if (fiber->capacity < nextstacktop) {
         janet_fiber_setcapacity(fiber, 2 * nextstacktop);
     }
@@ -241,13 +246,6 @@ int janet_fiber_funcframe_tail(JanetFiber *fiber, JanetFunction *func) {
     janet_fiber_frame(fiber)->pc = func->def->bytecode;
     janet_fiber_frame(fiber)->flags |= JANET_STACKFRAME_TAILCALL;
 
-    /* Check strict arity AFTER getting fiber to valid state. */
-    if (func->def->flags & JANET_FUNCDEF_FLAG_FIXARITY) {
-        if (func->def->arity != next_arity) {
-            return 1;
-        }
-    }
-
     /* Good return */
     return 0;
 }
diff --git a/src/core/vm.c b/src/core/vm.c
index 82407456..ec935f03 100644
--- a/src/core/vm.c
+++ b/src/core/vm.c
@@ -988,6 +988,10 @@ JanetSignal janet_call(
         JanetFiber **f) {
     JanetFiber *fiber = janet_fiber_n(fun, 64, argv, argn);
     if (f) *f = fiber;
+    if (!fiber) {
+        *out = janet_cstringv("arity mismatch");
+        return JANET_SIGNAL_ERROR;
+    }
     return janet_continue(fiber, janet_wrap_nil(), out);
 }
 
diff --git a/test/suite3.janet b/test/suite3.janet
index 89855e66..f115f95b 100644
--- a/test/suite3.janet
+++ b/test/suite3.janet
@@ -70,4 +70,8 @@
           (= (get res 3) 4)
           (= (get res 5) 6)) "loop :pairs")
 
+# Another regression test - no segfaults
+(defn afn [x] x)
+(assert (= 1 (try (afn) ([err] 1))) "calling function with wrong arity does not segfault.")
+
 (end-suite)