Re: [Tarantool-patches] [PATCH luajit] Fix recording of __concat metamethod.

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

Hi, Sergey

thanks for the patch! LGTM

On 3/11/24 15:30, Sergey Kaplun wrote:
> From: Mike Pall <mike>
>
> Thanks to Sergey Kaplun.
>
> (cherry picked from commit bcc5125a9188179d23c223b8865ed94951fb91b3)
>
> `lj_record_ret()` uses `J->L->base` as a base for recording
> concatenation with remaining operands, even if there is a vararg frame
> or pcall frame (so it uses the wrong Lua stack slots from a frame
> above). This leads to the corresponding assertion failure in the
> `lj_record_mm_lookup()`.
>
> This patch adds the calculation of the base adjusment necessary for
> correct frame usage.
>
> Sergey Kaplun:
> * added the description and the test for the problem
>
> Part of tarantool/tarantool#9595
> ---
>
> Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1164-record-meta-concat-varg-pcall
> Tarantool PR: https://github.com/tarantool/tarantool/pull/9788
> Related issues:
> * https://github.com/tarantool/tarantool/issues/9595
> * https://github.com/LuaJIT/LuaJIT/issues/1164
>
>   src/lj_record.c                               |  8 ++-
>   ...164-record-meta-concat-varg-pcall.test.lua | 49 +++++++++++++++++++
>   2 files changed, 55 insertions(+), 2 deletions(-)
>   create mode 100644 test/tarantool-tests/lj-1164-record-meta-concat-varg-pcall.test.lua
>
> diff --git a/src/lj_record.c b/src/lj_record.c
> index c01c1f0b..77818fec 100644
> --- a/src/lj_record.c
> +++ b/src/lj_record.c
> @@ -819,6 +819,7 @@ void lj_record_ret(jit_State *J, BCReg rbase, ptrdiff_t gotresults)
>   {
>     TValue *frame = J->L->base - 1;
>     ptrdiff_t i;
> +  BCReg baseadj = 0;
>     for (i = 0; i < gotresults; i++)
>       (void)getslot(J, rbase+i);  /* Ensure all results have a reference. */
>     while (frame_ispcall(frame)) {  /* Immediately resolve pcall() returns. */
> @@ -827,6 +828,7 @@ void lj_record_ret(jit_State *J, BCReg rbase, ptrdiff_t gotresults)
>         lj_trace_err(J, LJ_TRERR_NYIRETL);
>       lj_assertJ(J->baseslot > 1+LJ_FR2, "bad baseslot for return");
>       gotresults++;
> +    baseadj += cbase;
>       rbase += cbase;
>       J->baseslot -= (BCReg)cbase;
>       J->base -= cbase;
> @@ -851,6 +853,7 @@ void lj_record_ret(jit_State *J, BCReg rbase, ptrdiff_t gotresults)
>       if (--J->framedepth < 0)  /* NYI: return of vararg func to lower frame. */
>         lj_trace_err(J, LJ_TRERR_NYIRETL);
>       lj_assertJ(J->baseslot > 1+LJ_FR2, "bad baseslot for return");
> +    baseadj += cbase;
>       rbase += cbase;
>       J->baseslot -= (BCReg)cbase;
>       J->base -= cbase;
> @@ -918,7 +921,8 @@ void lj_record_ret(jit_State *J, BCReg rbase, ptrdiff_t gotresults)
>         BCReg bslot = bc_b(*(frame_contpc(frame)-1));
>         TRef tr = gotresults ? J->base[cbase+rbase] : TREF_NIL;
>         if (bslot != J->maxslot) {  /* Concatenate the remainder. */
> -	TValue *b = J->L->base, save;  /* Simulate lower frame and result. */
> +	/* Simulate lower frame and result. */
> +	TValue *b = J->L->base - baseadj, save;
>   	/* Can't handle MM_concat + CALLT + fast func side-effects. */
>   	if (J->postproc != LJ_POST_NONE)
>   	  lj_trace_err(J, LJ_TRERR_NYIRETL);
> @@ -931,7 +935,7 @@ void lj_record_ret(jit_State *J, BCReg rbase, ptrdiff_t gotresults)
>   	J->L->base = b - cbase;
>   	tr = rec_cat(J, bslot, cbase-(2<<LJ_FR2));
>   	b = J->L->base + cbase;  /* Undo. */
> -	J->L->base = b;
> +	J->L->base = b + baseadj;
>   	copyTV(J->L, b-(2<<LJ_FR2), &save);
>         }
>         if (tr) {  /* Store final result. */
> diff --git a/test/tarantool-tests/lj-1164-record-meta-concat-varg-pcall.test.lua b/test/tarantool-tests/lj-1164-record-meta-concat-varg-pcall.test.lua
> new file mode 100644
> index 00000000..987e49a0
> --- /dev/null
> +++ b/test/tarantool-tests/lj-1164-record-meta-concat-varg-pcall.test.lua
> @@ -0,0 +1,49 @@
> +local tap = require('tap')
> +
> +-- Test file to demonstrate the incorrect recording of the
> +-- `__concat` metamethod with the VARG or protected frame for the
> +-- function used in the `__concat`, when we have to record more
> +-- than 2 objects.
> +-- See also: https://github.com/LuaJIT/LuaJIT/issues/1164.
> +
> +local test = tap.test('lj-1164-record-meta-concat-varg-pcall'):skipcond({
> +  ['Test requires JIT enabled'] = not jit.status(),
> +})
> +
> +test:plan(2)
> +
> +jit.opt.start('hotloop=1')
> +
> +-- Table with the simplest varg metamethod to call.
> +local tab_varg = setmetatable({}, {
> +  __concat = function(...)
> +    local _, tab_obj = ...
> +    return tab_obj
> +  end,
> +})
> +
> +local result
> +for _ = 1, 4 do
> +  -- The concatenation has right to left associativity.
> +  result = '' .. '' .. tab_varg
> +end
> +
> +test:is(result, tab_varg, 'varg frame is recorded correctly')
> +
> +-- Table with the simplest protected metamethod.
> +local tab_pcall = setmetatable({}, {
> +  -- Need to use `__call` metamethod to make the object callable.
> +  __call = function(tab_obj)
> +    return tab_obj
> +  end,
> +  __concat = pcall,
> +})
> +
> +for _ = 1, 4 do
> +  -- The concatenation has right to left associativity.
> +  result = tab_pcall .. tab_pcall .. ''
> +end
> +
> +test:is(result, true, 'protected frame is recorded correctly')
> +
> +test:done(true)