From 1d5c2ce4e295562daddfe6ce8e470749f0d42542 Mon Sep 17 00:00:00 2001
From: Mike Pall <mike>
Date: Sun, 21 Oct 2012 19:15:03 +0200
Subject: Replace error with PANIC for callbacks from JIT-compiled code.
---
doc/ext_ffi_semantics.html | 16 ++++++++++++++++
src/lj_ccallback.c | 10 +++++++---
2 files changed, 23 insertions(+), 3 deletions(-)
diff --git a/doc/ext_ffi_semantics.html b/doc/ext_ffi_semantics.html
index f8da1e60..ab02f2b8 100644
--- a/doc/ext_ffi_semantics.html
+++ b/doc/ext_ffi_semantics.html
@@ -934,6 +934,22 @@ advisable in general. Do this only if you know the C function, that
called the callback, copes with the forced stack unwinding and doesn't
leak resources.
</p>
+<p>
+One thing that's not allowed, is to let an FFI call into a C function
+get JIT-compiled, which in turn calls a callback, calling into Lua again.
+Usually this attempt is caught by the interpreter first and the
+C function is blacklisted for compilation.
+</p>
+<p>
+However, this heuristic may fail under specific circumstances: e.g. a
+message polling function might not run Lua callbacks right away and the call
+gets JIT-compiled. If it later happens to call back into Lua, you'll get a
+VM PANIC with the message <tt>"bad callback"</tt>. Then you'll need to
+manually turn off JIT-compilation with
+<a href="ext_jit.html#jit_onoff_func"><tt>jit.off()</tt></a> for the
+surrounding Lua function that invokes such a message polling function (or
+similar).
+</p>
<h3 id="callback_resources">Callback resource handling</h3>
<p>
diff --git a/src/lj_ccallback.c b/src/lj_ccallback.c
index 430643ee..e1d03fcf 100644
--- a/src/lj_ccallback.c
+++ b/src/lj_ccallback.c
@@ -527,10 +527,14 @@ static void callback_conv_result(CTState *cts, lua_State *L, TValue *o)
lua_State * LJ_FASTCALL lj_ccallback_enter(CTState *cts, void *cf)
{
lua_State *L = cts->L;
+ global_State *g = cts->g;
lua_assert(L != NULL);
- if (gcref(cts->g->jit_L))
- lj_err_caller(gco2th(gcref(cts->g->jit_L)), LJ_ERR_FFI_BADCBACK);
- lj_trace_abort(cts->g); /* Never record across callback. */
+ if (gcref(g->jit_L)) {
+ setstrV(L, L->top++, lj_err_str(L, LJ_ERR_FFI_BADCBACK));
+ if (g->panic) g->panic(L);
+ exit(EXIT_FAILURE);
+ }
+ lj_trace_abort(g); /* Never record across callback. */
/* Setup C frame. */
cframe_prev(cf) = L->cframe;
setcframe_L(cf, L);
--
cgit v1.2.3-55-g6feb