Re: [Tarantool-patches] [PATCH luajit v2 2/3] Cleanup stack overflow handling.

[Sergey Kaplun via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Hi, Maxim!
Thanks for the fixes!
Please, consider my comments below.

On 22.11.23, Maksim Kokryashkin wrote:
> From: Mike Pall <mike>
> 
> Reported by Peter Cawley.
> 
> (cherry-picked from commit d2f6c55b05c716e5dbb479b7e684abaee7cf6e12)
> 

<snipped>

> ---
>  src/lj_state.c                                | 15 +++++--
>  .../lj-962-premature-stack-overflow.test.c    | 41 +++++++++++++++++++
>  2 files changed, 52 insertions(+), 4 deletions(-)
>  create mode 100644 test/tarantool-c-tests/lj-962-premature-stack-overflow.test.c
> 
> diff --git a/src/lj_state.c b/src/lj_state.c
> index 76153bad..d8a5134c 100644
> --- a/src/lj_state.c
> +++ b/src/lj_state.c
> @@ -121,8 +121,17 @@ void lj_state_shrinkstack(lua_State *L, MSize used)
>  void LJ_FASTCALL lj_state_growstack(lua_State *L, MSize need)
>  {
>    MSize n;
> -  if (L->stacksize > LJ_STACK_MAXEX)  /* Overflow while handling overflow? */
> -    lj_err_throw(L, LUA_ERRERR);
> +  if (L->stacksize >= LJ_STACK_MAXEX) {
> +    /* 4. Throw 'error in error handling' when we are _over_ the limit. */
> +    if (L->stacksize > LJ_STACK_MAXEX)
> +      lj_err_throw(L, LUA_ERRERR);  /* Does not invoke an error handler. */

I suggest covering this special case in our test.

> +    /* 1. We are _at_ the limit after the last growth. */
> +    if (!L->status) {  /* 2. Throw 'stack overflow'. */
> +      L->status = LUA_ERRRUN;  /* Prevent ending here again for pushed msg. */
> +      lj_err_msg(L, LJ_ERR_STKOV);  /* May invoke an error handler. */
> +    }
> +    /* 3. Add space (over the limit) for pushed message and error handler. */
> +  }
>    n = L->stacksize + need;
>    if (n > LJ_STACK_MAX) {
>      n += 2*LUA_MINSTACK;
> @@ -132,8 +141,6 @@ void LJ_FASTCALL lj_state_growstack(lua_State *L, MSize need)

<snipped>

>  void LJ_FASTCALL lj_state_growstack1(lua_State *L)
> diff --git a/test/tarantool-c-tests/lj-962-premature-stack-overflow.test.c b/test/tarantool-c-tests/lj-962-premature-stack-overflow.test.c
> new file mode 100644
> index 00000000..fd7557a7
> --- /dev/null
> +++ b/test/tarantool-c-tests/lj-962-premature-stack-overflow.test.c
> @@ -0,0 +1,41 @@
> +#include "lua.h"
> +#include "lauxlib.h"
> +
> +#include "test.h"
> +#include "utils.h"
> +
> +#include "lj_obj.h"

Minor: Please provide rationalization for "lj_obj.h" used here (a
comment about calculation of stack usage is enough).

> +#include "luaconf.h"
> +
> +static int cur_slots = -1;
> +
> +static int fill_stack(lua_State *L)
> +{
> +	cur_slots = L->base - tvref(L->stack);
> +
> +	while(lua_gettop(L) < LUAI_MAXSTACK) {
> +		cur_slots += 1;
> +		lua_pushinteger(L, 42);
> +	}
> +
> +	return 0;
> +}
> +
> +static int premature_stackoverflow(void *test_state)
> +{
> +	lua_State *L = test_state;
> +	lua_cpcall(L, fill_stack, NULL);
> +	assert_true(cur_slots == LUAI_MAXSTACK - 1);
> +	return TEST_EXIT_SUCCESS;
> +}
> +
> +int main(void)
> +{
> +	lua_State *L = utils_lua_init();
> +	const struct test_unit tgroup[] = {
> +		test_unit_def(premature_stackoverflow),
> +	};
> +	const int test_result = test_run_group(tgroup, L);
> +	utils_lua_close(L);
> +	return test_result;
> +}
> -- 
> 2.39.3 (Apple Git-145)
> 

-- 
Best regards,
Sergey Kaplun