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

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

[Maxim Kokryashkin via Tarantool-patches]

From: Mike Pall <mike>

Reported by Elias Oelschner. Analyzed by XmiliaH.

(cherry-picked from commit 3ee3c9cfa988339f1bf3068530515e2a6fb179d2)

During the recording of `__concat` methametod, the `rec_mm_arith`
function overrides stack slots that are not restored for GC64
mode later after the call. This leads to a segmentation fault
later on. This patch fixes the issue by accounting for those
additional slots in the array that is used to restore stack
values.

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

Part of tarantool/tarantool#9145
---
Branch: https://github.com/tarantool/luajit/tree/fckxorg/lj-839-concat-recording
PR: https://github.com/tarantool/tarantool/pull/9597
Issues: https://github.com/tarantool/tarantool/issues/9145
https://github.com/luajit/luajit/issues/839

 src/lj_record.c                               |  2 +-
 .../lj-839-concat-recording.test.lua          | 27 +++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)
 create mode 100644 test/tarantool-tests/lj-839-concat-recording.test.lua

diff --git a/src/lj_record.c b/src/lj_record.c
index a929b8aa..59549b03 100644
--- a/src/lj_record.c
+++ b/src/lj_record.c
@@ -1932,7 +1932,7 @@ static TRef rec_tnew(jit_State *J, uint32_t ah)
 static TRef rec_cat(jit_State *J, BCReg baseslot, BCReg topslot)
 {
   TRef *top = &J->base[topslot];
-  TValue savetv[5];
+  TValue savetv[5+LJ_FR2];
   BCReg s;
   RecordIndex ix;
   lj_assertJ(baseslot < topslot, "bad CAT arg");
diff --git a/test/tarantool-tests/lj-839-concat-recording.test.lua b/test/tarantool-tests/lj-839-concat-recording.test.lua
new file mode 100644
index 00000000..9ec0ed96
--- /dev/null
+++ b/test/tarantool-tests/lj-839-concat-recording.test.lua
@@ -0,0 +1,27 @@
+local tap = require('tap')
+local test = tap.test('lj-839-concat-recording'):skipcond({
+  ['Test requires JIT enabled'] = not jit.status(),
+})
+test:plan(1)
+
+-- Test file to demonstrate LuaJIT overriding stack slots without
+-- restoration during the recording of the concat metamethod.
+-- See also: https://github.com/LuaJIT/LuaJIT/issues/839.
+
+-- Setup value with the `__concat` metamethod.
+local v1 = setmetatable({}, {
+    __concat = function() return "" end,
+});
+
+jit.opt.start('hotloop=1')
+local result
+for _ = 1, 4 do
+  result = v1 .. ""  .. v1 ..  ""
+end
+
+-- There should be an empty string in case of success.
+-- Failure results in a segmentation fault.
+-- The issue is GC64-specific, yet it is still being tested for
+-- other builds.
+test:is(result, '', 'correct stack restoration')
+test:done(true)
--
2.43.0

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

[Sergey Kaplun via Tarantool-patches]

Hi, Maxim!
Thanks for the patch!
LGTM, after adding a comment about the magic sequence of values for the
concatenation (see the comment below).

On 15.01.24, Maxim Kokryashkin wrote:
> From: Mike Pall <mike>
> 
> Reported by Elias Oelschner. Analyzed by XmiliaH.
> 
> (cherry-picked from commit 3ee3c9cfa988339f1bf3068530515e2a6fb179d2)
> 
> During the recording of `__concat` methametod, the `rec_mm_arith`
> function overrides stack slots that are not restored for GC64
> mode later after the call. This leads to a segmentation fault
> later on. This patch fixes the issue by accounting for those
> additional slots in the array that is used to restore stack

Minor: "slots in the array that is used to restore" sounds a little
cumbersome.
I suggest to say  "slots in the array used for restoring"
Feel free to ignore.

> values.
> 
> Maxim Kokryashkin:
> * added the description and the test for the problem
> 
> Part of tarantool/tarantool#9145
> ---
> Branch: https://github.com/tarantool/luajit/tree/fckxorg/lj-839-concat-recording
> PR: https://github.com/tarantool/tarantool/pull/9597
> Issues: https://github.com/tarantool/tarantool/issues/9145
> https://github.com/luajit/luajit/issues/839
> 
>  src/lj_record.c                               |  2 +-
>  .../lj-839-concat-recording.test.lua          | 27 +++++++++++++++++++
>  2 files changed, 28 insertions(+), 1 deletion(-)
>  create mode 100644 test/tarantool-tests/lj-839-concat-recording.test.lua
> 
> diff --git a/src/lj_record.c b/src/lj_record.c
> index a929b8aa..59549b03 100644
> --- a/src/lj_record.c
> +++ b/src/lj_record.c
> @@ -1932,7 +1932,7 @@ static TRef rec_tnew(jit_State *J, uint32_t ah)
>  static TRef rec_cat(jit_State *J, BCReg baseslot, BCReg topslot)
>  {
>    TRef *top = &J->base[topslot];
> -  TValue savetv[5];
> +  TValue savetv[5+LJ_FR2];
>    BCReg s;
>    RecordIndex ix;
>    lj_assertJ(baseslot < topslot, "bad CAT arg");
> diff --git a/test/tarantool-tests/lj-839-concat-recording.test.lua b/test/tarantool-tests/lj-839-concat-recording.test.lua
> new file mode 100644
> index 00000000..9ec0ed96
> --- /dev/null
> +++ b/test/tarantool-tests/lj-839-concat-recording.test.lua
> @@ -0,0 +1,27 @@
> +local tap = require('tap')
> +local test = tap.test('lj-839-concat-recording'):skipcond({
> +  ['Test requires JIT enabled'] = not jit.status(),
> +})
> +test:plan(1)
> +
> +-- Test file to demonstrate LuaJIT overriding stack slots without
> +-- restoration during the recording of the concat metamethod.
> +-- See also: https://github.com/LuaJIT/LuaJIT/issues/839.
> +
> +-- Setup value with the `__concat` metamethod.
> +local v1 = setmetatable({}, {
> +    __concat = function() return "" end,

Typo: s/""/''/, according to the codestyle.

Nit: 2 extra whitespaces at the beginning.

> +});
> +
> +jit.opt.start('hotloop=1')
> +local result
> +for _ = 1, 4 do
> +  result = v1 .. ""  .. v1 ..  ""

Typo: s/""/''/g, according to the codestyle.

Why do we need exactly this sequence? Please add a comment.

> +end
> +
> +-- There should be an empty string in case of success.

Typo: s/case/the case/

> +-- Failure results in a segmentation fault.
> +-- The issue is GC64-specific, yet it is still being tested for
> +-- other builds.
> +test:is(result, '', 'correct stack restoration')
> +test:done(true)
> --
> 2.43.0
> 

-- 
Best regards,
Sergey Kaplun

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

[Sergey Bronnikov via Tarantool-patches]

Max, thanks for the patch!

LGTM

On 1/15/24 17:29, Maxim Kokryashkin wrote:
> From: Mike Pall <mike>
>
> Reported by Elias Oelschner. Analyzed by XmiliaH.
>
> (cherry-picked from commit 3ee3c9cfa988339f1bf3068530515e2a6fb179d2)
>
> During the recording of `__concat` methametod, the `rec_mm_arith`
> function overrides stack slots that are not restored for GC64
> mode later after the call. This leads to a segmentation fault
> later on. This patch fixes the issue by accounting for those
> additional slots in the array that is used to restore stack
> values.
>
> Maxim Kokryashkin:
> * added the description and the test for the problem
>
> Part of tarantool/tarantool#9145
> ---
> Branch: https://github.com/tarantool/luajit/tree/fckxorg/lj-839-concat-recording
> PR: https://github.com/tarantool/tarantool/pull/9597
> Issues: https://github.com/tarantool/tarantool/issues/9145
> https://github.com/luajit/luajit/issues/839
>
>   src/lj_record.c                               |  2 +-
>   .../lj-839-concat-recording.test.lua          | 27 +++++++++++++++++++
>   2 files changed, 28 insertions(+), 1 deletion(-)
>   create mode 100644 test/tarantool-tests/lj-839-concat-recording.test.lua
>
> diff --git a/src/lj_record.c b/src/lj_record.c
> index a929b8aa..59549b03 100644
> --- a/src/lj_record.c
> +++ b/src/lj_record.c
> @@ -1932,7 +1932,7 @@ static TRef rec_tnew(jit_State *J, uint32_t ah)
>   static TRef rec_cat(jit_State *J, BCReg baseslot, BCReg topslot)
>   {
>     TRef *top = &J->base[topslot];
> -  TValue savetv[5];
> +  TValue savetv[5+LJ_FR2];
>     BCReg s;
>     RecordIndex ix;
>     lj_assertJ(baseslot < topslot, "bad CAT arg");
> diff --git a/test/tarantool-tests/lj-839-concat-recording.test.lua b/test/tarantool-tests/lj-839-concat-recording.test.lua
> new file mode 100644
> index 00000000..9ec0ed96
> --- /dev/null
> +++ b/test/tarantool-tests/lj-839-concat-recording.test.lua
> @@ -0,0 +1,27 @@
> +local tap = require('tap')
> +local test = tap.test('lj-839-concat-recording'):skipcond({
> +  ['Test requires JIT enabled'] = not jit.status(),
> +})
> +test:plan(1)
> +
> +-- Test file to demonstrate LuaJIT overriding stack slots without
> +-- restoration during the recording of the concat metamethod.
> +-- See also: https://github.com/LuaJIT/LuaJIT/issues/839.
> +
> +-- Setup value with the `__concat` metamethod.
> +local v1 = setmetatable({}, {
> +    __concat = function() return "" end,
> +});
> +
> +jit.opt.start('hotloop=1')
> +local result
> +for _ = 1, 4 do
> +  result = v1 .. ""  .. v1 ..  ""
> +end
> +
> +-- There should be an empty string in case of success.
> +-- Failure results in a segmentation fault.
> +-- The issue is GC64-specific, yet it is still being tested for
> +-- other builds.
> +test:is(result, '', 'correct stack restoration')
> +test:done(true)
> --
> 2.43.0
>

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

[Sergey Kaplun via Tarantool-patches]

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)
-- 
2.44.0

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

[Sergey Bronnikov via Tarantool-patches]

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)

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

[Maxim Kokryashkin via Tarantool-patches]

Hi, Sergey!
Thanks for the patch!
LGTM!

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

[Sergey Kaplun via Tarantool-patches]

I've checked the patchset into all long-term branches in
tarantool/luajit and bumped a new version in master [1], release/3.0 [2]
and release/2.11 [3].

[1]: https://github.com/tarantool/tarantool/pull/9832
[2]: https://github.com/tarantool/tarantool/pull/9833
[3]: https://github.com/tarantool/tarantool/pull/9834

-- 
Best regards,
Sergey Kaplun