Handle all stack layouts in (delayed) TRACE vmevent.

Thanks to Sergey Bronnikov and Peter Cawley.

(cherry picked from commit b138ccf)

When recording a trace using a Lua code like
`repeat until `a >= 'b' > 'b'` a Lua error is encountered
(`attempt to compare string with nil`), which (along with
raising the error) causes an asynchronous trace abort.
The trace abort remains pending until the next reentrance to the
LuaJIT VM via `lj_vm_call()` or `lj_vm_pcall().

On handling abort LuaJIT is searching for the topmost Lua frame
on the stack, that was active when the trace abort happened,
it is needed to generate a better error message.
Unfortunately, because the abort was due to an error, and
the error was caught by a `lua_pcall` with an unspecified
error function (4th argument), the Lua frame that caused the abort
was already removed as part of error processing, so the search
cannot find it. Furthermore, in this particular case, there are
no Lua frames on the stack, which isn't something the search code
had considered possible.

Sergey Bronnikov:
* added the description and the test for the problem

Part of tarantool/tarantool#11055

Reviewed-by: Sergey Kaplun <[email protected]>
Signed-off-by: Sergey Kaplun <[email protected]>
(cherry picked from commit b98550d)

src/lj_trace.c

@@ -616,21 +616,27 @@ static int trace_abort(jit_State *J)
     J->cur.link = 0;
     J->cur.linktype = LJ_TRLINK_NONE;
     lj_vmevent_send(L, TRACE,
-      TValue *frame;
+      cTValue *bot = tvref(L->stack)+LJ_FR2;
+      cTValue *frame;
       const BCIns *pc;
-      GCfunc *fn;
+      BCPos pos = 0;
       setstrV(L, L->top++, lj_str_newlit(L, "abort"));
       setintV(L->top++, traceno);
       /* Find original Lua function call to generate a better error message. */
-      frame = J->L->base-1;
-      pc = J->pc;
-      while (!isluafunc(frame_func(frame))) {
-	pc = (frame_iscont(frame) ? frame_contpc(frame) : frame_pc(frame)) - 1;
-	frame = frame_prev(frame);
+      for (frame = J->L->base-1, pc = J->pc; ; frame = frame_prev(frame)) {
+	if (isluafunc(frame_func(frame))) {
+	  pos = proto_bcpos(funcproto(frame_func(frame)), pc);
+	  break;
+	} else if (frame_prev(frame) <= bot) {
+	  break;
+	} else if (frame_iscont(frame)) {
+	  pc = frame_contpc(frame) - 1;
+	} else {
+	  pc = frame_pc(frame) - 1;
+	}
       }
-      fn = frame_func(frame);
-      setfuncV(L, L->top++, fn);
-      setintV(L->top++, proto_bcpos(funcproto(fn), pc));
+      setfuncV(L, L->top++, frame_func(frame));
+      setintV(L->top++, pos);
       copyTV(L, L->top++, restorestack(L, errobj));
       copyTV(L, L->top++, &J->errinfo);
     );

test/tarantool-c-tests/lj-1087-vm-handler-call.test.c

@@ -0,0 +1,170 @@
+#include "lua.h"
+#include "lauxlib.h"
+
+#include "test.h"
+#include "utils.h"
+
+/* Need for skipcond for BSD and JIT. */
+#include "lj_arch.h"
+
+/* XXX: Still need normal assert for sanity checks. */
+#undef NDEBUG
+#include <assert.h>
+
+/*
+ * Test file to demonstrate a segmentation fault, when a C
+ * function is used as a VM handler for trace events in LuaJIT:
+ *
+ * Program received signal SIGSEGV, Segmentation fault.
+ * 0x000055555557e77d in trace_abort (J=0x7ffff7f9b6b8) at lj_trace.c:615
+ * 615         lj_vmevent_send(L, TRACE,
+ * (gdb) bt
+ *
+ * See details in https://github.com/LuaJIT/LuaJIT/issues/1087.
+ */
+
+static int nop(lua_State *L)
+{
+	UNUSED(L);
+	return 0;
+}
+
+/* Note, `event == NULL` disables the corresponding handler. */
+static void jit_attach(lua_State *L, lua_CFunction cb, const char *event)
+{
+	lua_getglobal(L, "jit");
+	lua_getfield(L, -1, "attach");
+	lua_pushcfunction(L, cb);
+	if (event != NULL)
+		lua_pushstring(L, event);
+	else
+		lua_pushnil(L);
+	lua_pcall(L, 2, 0, 0);
+}
+
+static int handle_luafunc_frame(void *test_state)
+{
+	/* Setup. */
+	lua_State *L = test_state;
+	jit_attach(L, nop, "trace");
+
+	/* Loading and executing of a broken Lua code. */
+	int rc = luaL_dostring(L, "repeat until nil > 1");
+	assert(rc == 1);
+
+	/* The Lua chunk generates a Lua frame. */
+	rc = luaL_dostring(L, "return function() end");
+	assert(rc == 0);
+
+	/* Teardown. */
+	lua_settop(L, 0);
+
+	return TEST_EXIT_SUCCESS;
+}
+
+static int cframe(lua_State *L)
+{
+	int rc = luaL_dostring(L, "repeat until nil > 1");
+	assert(rc == 1);
+	/* Remove errmsg. */
+	lua_pop(L, 1);
+
+	lua_pushcfunction(L, nop);
+	lua_call(L, 0, 0);
+
+	return 0;
+}
+
+static int handle_c_frame(void *test_state)
+{
+	/* Setup. */
+	lua_State *L = test_state;
+	jit_attach(L, nop, "trace");
+
+	lua_pushcfunction(L, cframe);
+	lua_call(L, 0, 0);
+
+	/* Teardown. */
+	lua_settop(L, 0);
+
+	return TEST_EXIT_SUCCESS;
+}
+
+static int handle_cont_frame(void *test_state)
+{
+	const char lua_chunk[] =
+		"local t = setmetatable({}, { __index = global_f })"
+		"for i = 1, 4 do"
+		"    _ = t[1]"
+		"end";
+
+	/* Setup. */
+	lua_State *L = test_state;
+	jit_attach(L, nop, "trace");
+
+	/*
+	 * The number 32767 is `REF_DROP - REF_BIAS`. This is the
+	 * maximum possible IR amount, so the trace is always
+	 * aborted.
+	 */
+	int res = luaL_dostring(L, "jit.opt.start('minstitch=32767')");
+	assert(res == 0);
+	lua_pushcfunction(L, nop);
+	lua_setglobal(L, "global_f");
+
+	res = luaL_dostring(L, lua_chunk);
+	assert(res == 0);
+
+	/* Teardown. */
+	lua_settop(L, 0);
+	res = luaL_dostring(L, "jit.opt.start('minstitch=0')");
+	assert(res == 0);
+
+	return TEST_EXIT_SUCCESS;
+}
+
+static int handle_bottom_frame(void *test_state)
+{
+	lua_State *L = test_state;
+
+	/* Attach VM call handler. */
+	jit_attach(L, nop, "trace");
+
+	/* Load a Lua code that generate a trace abort. */
+	int rc = luaL_dostring(L, "repeat until nil > 1");
+	assert(rc == 1);
+
+	/*
+	 * Note, protected call is used inside `jit_attach()` to
+	 * return to the VM on disabling the handler. Then
+	 * a segmentation fault is triggered.
+	 */
+	jit_attach(L, nop, NULL);
+
+	/* Teardown. */
+	lua_settop(L, 0);
+
+	return TEST_EXIT_SUCCESS;
+}
+
+int main(void)
+{
+	if (!LJ_HASJIT)
+		return skip_all("JIT is disabled");
+
+	if (LUAJIT_OS == LUAJIT_OS_BSD)
+		return skip_all("Disabled on *BSD due to #4819");
+
+	lua_State *L = utils_lua_init();
+	const struct test_unit tgroup[] = {
+		test_unit_def(handle_luafunc_frame),
+		test_unit_def(handle_bottom_frame),
+		test_unit_def(handle_cont_frame),
+		test_unit_def(handle_c_frame),
+	};
+	int res = luaL_dostring(L, "jit.opt.start('hotloop=1')");
+	assert(res == 0);
+	const int test_result = test_run_group(tgroup, L);
+	utils_lua_close(L);
+	return test_result;
+}