[Tarantool-patches] [PATCH luajit v2 5/5] Restore cur_L for specific Lua/C API use case.

[Maxim Kokryashkin]

From: Mike Pall <mike>

Thanks to Peter Cawley.

(cherry-picked from commit e86990f7f24a94b0897061f25a84547fe1108bed)

Consider the following Lua C API function:

```
static int error_after_coroutine_return(lua_State *L)
{
	lua_State *innerL = lua_newthread(L);
	luaL_loadstring(innerL, "print('inner coro')");
	lua_pcall(innerL, 0, 0, 0);
	luaL_error(L, "my fancy error");
	return 0;
}
```

And the following Lua script:
```
local libcur_L = require('libcur_L')

local function onesnap_f(var)
  if var then
    return 1
  else
    return 0
  end
end

-- Compile function to trace with snapshot.
if jit then jit.opt.start('hotloop=1') end
onesnap_f(true)
onesnap_f(true)

local r, s = pcall(libcur_L.error_after_coroutine_return)
onesnap_f(false)
```

This is the only case when `cur_L` is not restored, according to
the analysis done in https://github.com/LuaJIT/LuaJIT/issues/1066.

This patch changes the error-catching routine, so now the patch
sets the actual cur_L there.
Now it is possible to throw errors on non-executing coroutines,
which is a violation of the Lua C API. So, even though it is now
possible, that behavior should be avoided anyway.

Maxim Kokryashkin:
* added the description and the test for the problem

Resolves tarantool/tarantool#6323
---
 src/lj_err.c                                  |  5 ++-
 test/tarantool-tests/CMakeLists.txt           |  1 +
 ...-fix-cur_L-after-coroutine-resume.test.lua | 32 +++++++++++++++++++
 .../CMakeLists.txt                            |  1 +
 .../libcur_L_coroutine.c                      | 22 +++++++++++++
 5 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume.test.lua
 create mode 100644 test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume/CMakeLists.txt
 create mode 100644 test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume/libcur_L_coroutine.c

diff --git a/src/lj_err.c b/src/lj_err.c
index 46fb81ee..1a9a2f2b 100644
--- a/src/lj_err.c
+++ b/src/lj_err.c
@@ -174,12 +174,15 @@ static void *err_unwind(lua_State *L, void *stopcf, int errcode)
     case FRAME_PCALL:  /* FF pcall() frame. */
     case FRAME_PCALLH:  /* FF pcall() frame inside hook. */
       if (errcode) {
+	global_State *g;
 	if (errcode == LUA_YIELD) {
 	  frame = frame_prevd(frame);
 	  break;
 	}
+	g = G(L);
+	setgcref(g->cur_L, obj2gco(L));
 	if (frame_typep(frame) == FRAME_PCALL)
-	  hook_leave(G(L));
+	  hook_leave(g);
 	L->base = frame_prevd(frame) + 1;
 	L->cframe = cf;
 	unwindstack(L, L->base);
diff --git a/test/tarantool-tests/CMakeLists.txt b/test/tarantool-tests/CMakeLists.txt
index c15d6037..d84072e0 100644
--- a/test/tarantool-tests/CMakeLists.txt
+++ b/test/tarantool-tests/CMakeLists.txt
@@ -68,6 +68,7 @@ add_subdirectory(lj-727-lightuserdata-itern)
 add_subdirectory(lj-802-panic-at-mcode-protfail)
 add_subdirectory(lj-flush-on-trace)
 add_subdirectory(lj-1004-oom-error-frame)
+add_subdirectory(lj-1066-fix-cur_L-after-coroutine-resume)
 
 # The part of the memory profiler toolchain is located in tools
 # directory, jit, profiler, and bytecode toolchains are located
diff --git a/test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume.test.lua b/test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume.test.lua
new file mode 100644
index 00000000..3919ae23
--- /dev/null
+++ b/test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume.test.lua
@@ -0,0 +1,32 @@
+local tap = require('tap')
+local test = tap.test('lj-1066-fix-cur_L-after-coroutine-resume'):skipcond({
+  ['Test requires JIT enabled'] = not jit.status(),
+})
+
+test:plan(1)
+
+local libcur_L_coroutine = require('libcur_L_coroutine')
+
+local function cbool(cond)
+  if cond then
+    return 1
+  else
+    return 0
+  end
+end
+
+-- Compile function to trace with snapshot.
+jit.opt.start('hotloop=1')
+-- First call makes `cbool()` hot enough to be recorded next time.
+cbool(true)
+-- Second call records `cbool()` body (i.e. `if` branch). This is
+-- a root trace for `cbool()`.
+cbool(true)
+
+local res = pcall(libcur_L_coroutine.error_after_coroutine_return)
+assert(res == false, "return from error")
+-- Call with restoration from a snapshot with wrong cur_L.
+cbool(false)
+
+test:ok(true)
+test:done(true)
diff --git a/test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume/CMakeLists.txt b/test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume/CMakeLists.txt
new file mode 100644
index 00000000..c8a3731f
--- /dev/null
+++ b/test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume/CMakeLists.txt
@@ -0,0 +1 @@
+BuildTestCLib(libcur_L_coroutine libcur_L_coroutine.c)
diff --git a/test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume/libcur_L_coroutine.c b/test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume/libcur_L_coroutine.c
new file mode 100644
index 00000000..7a71d0f0
--- /dev/null
+++ b/test/tarantool-tests/lj-1066-fix-cur_L-after-coroutine-resume/libcur_L_coroutine.c
@@ -0,0 +1,22 @@
+#include "lua.h"
+#include "lauxlib.h"
+
+static int error_after_coroutine_return(lua_State *L)
+{
+	lua_State *innerL = lua_newthread(L);
+	luaL_loadstring(innerL, "print('inner coro')");
+	lua_pcall(innerL, 0, 0, 0);
+	luaL_error(L, "my fancy error");
+	return 0;
+}
+
+static const struct luaL_Reg libcur_L_coroutine[] = {
+	{"error_after_coroutine_return", error_after_coroutine_return},
+	{NULL, NULL}
+};
+
+LUA_API int luaopen_libcur_L_coroutine(lua_State *L)
+{
+	luaL_register(L, "libcur_L_coroutine", libcur_L_coroutine);
+	return 1;
+}
-- 
2.42.0