[Tarantool-patches] [PATCH luajit] Fix predict_next() in parser.

[Tarantool-patches] [PATCH luajit] Fix predict_next() in parser.

[Sergey Kaplun via Tarantool-patches]

From: Mike Pall <mike>

Reported by Sergey Kaplun.

(cherry-picked from commit caf7cbc57c945f7b68871ad72abafb2b6e6fb7f5)

Assume, we have the following Lua code:
| local _
| for _ in (nil):foo() do end

The first part of the bytecode emitted for it is the following:
| 0001    KNIL     0   1
| 0002    MOV      2   1
| 0003    TGETS    1   1   0  ; "foo"
| 0004    CALL     1   4   2

The `0001 KNIL` is a result of merging two `KPRI` instructions: one for
the local variable, one for the slot with `nil` object. During parsing in
`predict_next()` the second `MOV` bytecode is examined to set `pairs` or
`next` local variable. But, as far as it moves `nil` value, that isn't
an actual variable, so it has no the name this leads to the crash.

This patch adds the check to be sure that `RD` in the `MOV` bytecode is
an actual variable.

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

Part of tarantool/tarantool#8825
---

Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1033-fix-parsing-predict-next
PR: https://github.com/tarantool/tarantool/pull/8987
Related issues:
* https://github.com/LuaJIT/LuaJIT/issues/1033
* https://github.com/tarantool/tarantool/issues/8825

 src/lj_parse.c                                |  1 +
 .../lj-1033-fix-parsing-predict-next.test.lua | 30 +++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua

diff --git a/src/lj_parse.c b/src/lj_parse.c
index 3f6caaec..420b95cb 100644
--- a/src/lj_parse.c
+++ b/src/lj_parse.c
@@ -2532,6 +2532,7 @@ static int predict_next(LexState *ls, FuncState *fs, BCPos pc)
   cTValue *o;
   switch (bc_op(ins)) {
   case BC_MOV:
+    if (bc_d(ins) >= fs->nactvar) return 0;
     name = gco2str(gcref(var_get(ls, fs, bc_d(ins)).name));
     break;
   case BC_UGET:
diff --git a/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
new file mode 100644
index 00000000..624344eb
--- /dev/null
+++ b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
@@ -0,0 +1,30 @@
+local tap = require('tap')
+local test = tap.test('lj-1033-fix-parsing-predict-next')
+
+test:plan(3)
+
+local res_f = loadstring([[
+-- This local variable is necessary, because it emits `KPRI`
+-- bytecode, with which the next `KPRI` bytecode will be merged.
+--
+-- The resulting bytecode is the following:
+--
+-- 0001    KNIL     0   1
+-- 0002    MOV      2   1
+-- 0003    TGETS    1   1   0  ; "foo"
+-- 0004    CALL     1   4   2
+--
+-- This MOV don't use any variable value from the stack, so the
+-- attempt to get the name in `predict_next() leads to the crash.
+local _
+for _ in (nil):foo() do end
+]])
+
+test:ok(res_f, 'chunk loaded sucsessfully')
+
+local res, err = pcall(res_f)
+
+test:ok(not res, 'loaded function not executed')
+test:like(err, 'attempt to index a nil value', 'correct error message')
+
+test:done(true)
-- 
2.41.0

Re: [Tarantool-patches] [PATCH luajit] Fix predict_next() in parser.

[Maxim Kokryashkin via Tarantool-patches]

Hi, Sergey!
Thanks for the patch!
LGTM, except for a few nits below.
On Tue, Aug 15, 2023 at 05:25:41PM +0300, Sergey Kaplun wrote:
> From: Mike Pall <mike>
> 
> Reported by Sergey Kaplun.
> 
> (cherry-picked from commit caf7cbc57c945f7b68871ad72abafb2b6e6fb7f5)
> 
> Assume, we have the following Lua code:
> | local _
> | for _ in (nil):foo() do end
> 
> The first part of the bytecode emitted for it is the following:
> | 0001    KNIL     0   1
> | 0002    MOV      2   1
> | 0003    TGETS    1   1   0  ; "foo"
> | 0004    CALL     1   4   2
> 
> The `0001 KNIL` is a result of merging two `KPRI` instructions: one for
> the local variable, one for the slot with `nil` object. During parsing in
> `predict_next()` the second `MOV` bytecode is examined to set `pairs` or
> `next` local variable. But, as far as it moves `nil` value, that isn't
> an actual variable, so it has no the name this leads to the crash.
Typo: s/variable, so it/variable and/
Typo: s/the name this/name, that move/
> 
> This patch adds the check to be sure that `RD` in the `MOV` bytecode is
Typo: s/the check/a check/
> an actual variable.
Please mention the lj_bc.h here, so it is obvious what `RD` is.
> 
> Sergey Kaplun:
> * added the description and the test for the problem
> 
> Part of tarantool/tarantool#8825
> ---
> 
> Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1033-fix-parsing-predict-next
> PR: https://github.com/tarantool/tarantool/pull/8987
> Related issues:
> * https://github.com/LuaJIT/LuaJIT/issues/1033
> * https://github.com/tarantool/tarantool/issues/8825
> 
>  src/lj_parse.c                                |  1 +
>  .../lj-1033-fix-parsing-predict-next.test.lua | 30 +++++++++++++++++++
>  2 files changed, 31 insertions(+)
>  create mode 100644 test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> 
> diff --git a/src/lj_parse.c b/src/lj_parse.c
> index 3f6caaec..420b95cb 100644
> --- a/src/lj_parse.c
> +++ b/src/lj_parse.c
> @@ -2532,6 +2532,7 @@ static int predict_next(LexState *ls, FuncState *fs, BCPos pc)
>    cTValue *o;
>    switch (bc_op(ins)) {
>    case BC_MOV:
> +    if (bc_d(ins) >= fs->nactvar) return 0;
>      name = gco2str(gcref(var_get(ls, fs, bc_d(ins)).name));
>      break;
>    case BC_UGET:
> diff --git a/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> new file mode 100644
> index 00000000..624344eb
> --- /dev/null
> +++ b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> @@ -0,0 +1,30 @@
> +local tap = require('tap')
> +local test = tap.test('lj-1033-fix-parsing-predict-next')
> +
> +test:plan(3)
> +
> +local res_f = loadstring([[
> +-- This local variable is necessary, because it emits `KPRI`
> +-- bytecode, with which the next `KPRI` bytecode will be merged.
> +--
> +-- The resulting bytecode is the following:
> +--
> +-- 0001    KNIL     0   1
> +-- 0002    MOV      2   1
> +-- 0003    TGETS    1   1   0  ; "foo"
> +-- 0004    CALL     1   4   2
> +--
> +-- This MOV don't use any variable value from the stack, so the
Typo: s/don't/doesn't/
> +-- attempt to get the name in `predict_next() leads to the crash.
> +local _
> +for _ in (nil):foo() do end
> +]])
> +
> +test:ok(res_f, 'chunk loaded sucsessfully')
> +
> +local res, err = pcall(res_f)
> +
> +test:ok(not res, 'loaded function not executed')
> +test:like(err, 'attempt to index a nil value', 'correct error message')
> +
> +test:done(true)
> -- 
> 2.41.0
> 

Re: [Tarantool-patches] [PATCH luajit] Fix predict_next() in parser.

[Sergey Kaplun via Tarantool-patches]

Hi, Maxim!
Thanks for the review!
Fixed your comments inline.
Branch is force-pushed.

On 16.08.23, Maxim Kokryashkin wrote:
> Hi, Sergey!
> Thanks for the patch!
> LGTM, except for a few nits below.
> On Tue, Aug 15, 2023 at 05:25:41PM +0300, Sergey Kaplun wrote:
> > From: Mike Pall <mike>
> > 
> > Reported by Sergey Kaplun.
> > 

<snipped>

> > The `0001 KNIL` is a result of merging two `KPRI` instructions: one for
> > the local variable, one for the slot with `nil` object. During parsing in
> > `predict_next()` the second `MOV` bytecode is examined to set `pairs` or
> > `next` local variable. But, as far as it moves `nil` value, that isn't
> > an actual variable, so it has no the name this leads to the crash.
> Typo: s/variable, so it/variable and/
> Typo: s/the name this/name, that move/

Fixed.

> > 
> > This patch adds the check to be sure that `RD` in the `MOV` bytecode is
> Typo: s/the check/a check/

Fixed.

> > an actual variable.
> Please mention the lj_bc.h here, so it is obvious what `RD` is.

Fixed.

> > 
> > Sergey Kaplun:
> > * added the description and the test for the problem
> > 
> > Part of tarantool/tarantool#8825
> > ---
> > 
> > Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1033-fix-parsing-predict-next
> > PR: https://github.com/tarantool/tarantool/pull/8987
> > Related issues:
> > * https://github.com/LuaJIT/LuaJIT/issues/1033
> > * https://github.com/tarantool/tarantool/issues/8825
> > 
> >  src/lj_parse.c                                |  1 +
> >  .../lj-1033-fix-parsing-predict-next.test.lua | 30 +++++++++++++++++++
> >  2 files changed, 31 insertions(+)
> >  create mode 100644 test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> > 
> > diff --git a/src/lj_parse.c b/src/lj_parse.c
> > index 3f6caaec..420b95cb 100644
> > --- a/src/lj_parse.c
> > +++ b/src/lj_parse.c

<snipped>

> > +-- The resulting bytecode is the following:
> > +--
> > +-- 0001    KNIL     0   1
> > +-- 0002    MOV      2   1
> > +-- 0003    TGETS    1   1   0  ; "foo"
> > +-- 0004    CALL     1   4   2
> > +--
> > +-- This MOV don't use any variable value from the stack, so the
> Typo: s/don't/doesn't/

Fixed. See the iterative diff below:

===================================================================
diff --git a/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
index 624344eb..63998d8c 100644
--- a/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
+++ b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
@@ -14,7 +14,7 @@ local res_f = loadstring([[
 -- 0003    TGETS    1   1   0  ; "foo"
 -- 0004    CALL     1   4   2
 --
--- This MOV don't use any variable value from the stack, so the
+-- This MOV doesn't use any variable value from the stack, so the
 -- attempt to get the name in `predict_next() leads to the crash.
 local _
 for _ in (nil):foo() do end
===================================================================

<snipped>

> > 

-- 
Best regards,
Sergey Kaplun

Re: [Tarantool-patches] [PATCH luajit] Fix predict_next() in parser.

[Sergey Bronnikov via Tarantool-patches]

Hi, Sergey


thanks for the patch! See comments inline.


On 8/15/23 17:25, Sergey Kaplun wrote:
> From: Mike Pall <mike>
>
> Reported by Sergey Kaplun.
>
> (cherry-picked from commit caf7cbc57c945f7b68871ad72abafb2b6e6fb7f5)
>
> Assume, we have the following Lua code:
> | local _
> | for _ in (nil):foo() do end
>
> The first part of the bytecode emitted for it is the following:
> | 0001    KNIL     0   1
> | 0002    MOV      2   1
> | 0003    TGETS    1   1   0  ; "foo"
> | 0004    CALL     1   4   2
>
> The `0001 KNIL` is a result of merging two `KPRI` instructions: one for
> the local variable, one for the slot with `nil` object. During parsing in
> `predict_next()` the second `MOV` bytecode is examined to set `pairs` or
> `next` local variable. But, as far as it moves `nil` value, that isn't
> an actual variable, so it has no the name this leads to the crash.
>
> This patch adds the check to be sure that `RD` in the `MOV` bytecode is
> an actual variable.
>
> Sergey Kaplun:
> * added the description and the test for the problem
>
> Part of tarantool/tarantool#8825
> ---
>
> Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1033-fix-parsing-predict-next
> PR: https://github.com/tarantool/tarantool/pull/8987
> Related issues:
> * https://github.com/LuaJIT/LuaJIT/issues/1033
> * https://github.com/tarantool/tarantool/issues/8825
>
>   src/lj_parse.c                                |  1 +
>   .../lj-1033-fix-parsing-predict-next.test.lua | 30 +++++++++++++++++++
>   2 files changed, 31 insertions(+)
>   create mode 100644 test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
>
> diff --git a/src/lj_parse.c b/src/lj_parse.c
> index 3f6caaec..420b95cb 100644
> --- a/src/lj_parse.c
> +++ b/src/lj_parse.c
> @@ -2532,6 +2532,7 @@ static int predict_next(LexState *ls, FuncState *fs, BCPos pc)
>     cTValue *o;
>     switch (bc_op(ins)) {
>     case BC_MOV:
> +    if (bc_d(ins) >= fs->nactvar) return 0;
>       name = gco2str(gcref(var_get(ls, fs, bc_d(ins)).name));
>       break;
>     case BC_UGET:
> diff --git a/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> new file mode 100644
> index 00000000..624344eb
> --- /dev/null
> +++ b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> @@ -0,0 +1,30 @@
> +local tap = require('tap')
> +local test = tap.test('lj-1033-fix-parsing-predict-next')
> +
> +test:plan(3)
> +
> +local res_f = loadstring([[
> +-- This local variable is necessary, because it emits `KPRI`
> +-- bytecode, with which the next `KPRI` bytecode will be merged.
> +--
> +-- The resulting bytecode is the following:
> +--
> +-- 0001    KNIL     0   1
> +-- 0002    MOV      2   1
> +-- 0003    TGETS    1   1   0  ; "foo"
> +-- 0004    CALL     1   4   2
> +--
> +-- This MOV don't use any variable value from the stack, so the
> +-- attempt to get the name in `predict_next() leads to the crash.
What is a point to put a comment inside loadstring, not before it?
> +local _
> +for _ in (nil):foo() do end
> +]])
> +
> +test:ok(res_f, 'chunk loaded sucsessfully')
typo: sucsessfully -> successfully
> +
> +local res, err = pcall(res_f)
> +
> +test:ok(not res, 'loaded function not executed')

it is not clear for me what for do you need checking result code. I 
would omit it.

Feel free to ignore.


> +test:like(err, 'attempt to index a nil value', 'correct error message')
> +
> +test:done(true)

Re: [Tarantool-patches] [PATCH luajit] Fix predict_next() in parser.

[Sergey Kaplun via Tarantool-patches]

Hi, Sergey!
Thanks for the review!
Fixed your comments inline.

On 21.08.23, Sergey Bronnikov wrote:
> Hi, Sergey
> 
> 
> thanks for the patch! See comments inline.
> 
> 
> On 8/15/23 17:25, Sergey Kaplun wrote:
> > From: Mike Pall <mike>
> >
> > Reported by Sergey Kaplun.
> >
> > (cherry-picked from commit caf7cbc57c945f7b68871ad72abafb2b6e6fb7f5)
> >
> > Assume, we have the following Lua code:
> > | local _
> > | for _ in (nil):foo() do end
> >
> > The first part of the bytecode emitted for it is the following:
> > | 0001    KNIL     0   1
> > | 0002    MOV      2   1
> > | 0003    TGETS    1   1   0  ; "foo"
> > | 0004    CALL     1   4   2
> >
> > The `0001 KNIL` is a result of merging two `KPRI` instructions: one for
> > the local variable, one for the slot with `nil` object. During parsing in
> > `predict_next()` the second `MOV` bytecode is examined to set `pairs` or
> > `next` local variable. But, as far as it moves `nil` value, that isn't
> > an actual variable, so it has no the name this leads to the crash.
> >
> > This patch adds the check to be sure that `RD` in the `MOV` bytecode is
> > an actual variable.
> >
> > Sergey Kaplun:
> > * added the description and the test for the problem
> >
> > Part of tarantool/tarantool#8825
> > ---
> >
> > Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1033-fix-parsing-predict-next
> > PR: https://github.com/tarantool/tarantool/pull/8987
> > Related issues:
> > * https://github.com/LuaJIT/LuaJIT/issues/1033
> > * https://github.com/tarantool/tarantool/issues/8825
> >
> >   src/lj_parse.c                                |  1 +
> >   .../lj-1033-fix-parsing-predict-next.test.lua | 30 +++++++++++++++++++
> >   2 files changed, 31 insertions(+)
> >   create mode 100644 test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> >
> > diff --git a/src/lj_parse.c b/src/lj_parse.c
> > index 3f6caaec..420b95cb 100644
> > --- a/src/lj_parse.c
> > +++ b/src/lj_parse.c
> > @@ -2532,6 +2532,7 @@ static int predict_next(LexState *ls, FuncState *fs, BCPos pc)
> >     cTValue *o;
> >     switch (bc_op(ins)) {
> >     case BC_MOV:
> > +    if (bc_d(ins) >= fs->nactvar) return 0;
> >       name = gco2str(gcref(var_get(ls, fs, bc_d(ins)).name));
> >       break;
> >     case BC_UGET:
> > diff --git a/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> > new file mode 100644
> > index 00000000..624344eb
> > --- /dev/null
> > +++ b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> > @@ -0,0 +1,30 @@
> > +local tap = require('tap')
> > +local test = tap.test('lj-1033-fix-parsing-predict-next')
> > +
> > +test:plan(3)
> > +
> > +local res_f = loadstring([[
> > +-- This local variable is necessary, because it emits `KPRI`
> > +-- bytecode, with which the next `KPRI` bytecode will be merged.
> > +--
> > +-- The resulting bytecode is the following:
> > +--
> > +-- 0001    KNIL     0   1
> > +-- 0002    MOV      2   1
> > +-- 0003    TGETS    1   1   0  ; "foo"
> > +-- 0004    CALL     1   4   2
> > +--
> > +-- This MOV don't use any variable value from the stack, so the
> > +-- attempt to get the name in `predict_next() leads to the crash.
> What is a point to put a comment inside loadstring, not before it?

Moved the part about bytecode before. Still assume, that comment about
the variable is needed inside the code (i.e. this variable).

> > +local _
> > +for _ in (nil):foo() do end
> > +]])
> > +
> > +test:ok(res_f, 'chunk loaded sucsessfully')
> typo: sucsessfully -> successfully

Fixed, thanks!

> > +
> > +local res, err = pcall(res_f)
> > +
> > +test:ok(not res, 'loaded function not executed')
> 
> it is not clear for me what for do you need checking result code. I 
> would omit it.
> 
> Feel free to ignore.

Added the following comment to avoid confusing (see the whole iterative
patch below):

===================================================================
diff --git a/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
index 63998d8c..fed3ff6c 100644
--- a/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
+++ b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
@@ -3,10 +3,6 @@ local test = tap.test('lj-1033-fix-parsing-predict-next')
 
 test:plan(3)
 
-local res_f = loadstring([[
--- This local variable is necessary, because it emits `KPRI`
--- bytecode, with which the next `KPRI` bytecode will be merged.
---
 -- The resulting bytecode is the following:
 --
 -- 0001    KNIL     0   1
@@ -16,14 +12,18 @@ local res_f = loadstring([[
 --
 -- This MOV doesn't use any variable value from the stack, so the
 -- attempt to get the name in `predict_next() leads to the crash.
+local res_f = loadstring([[
+-- This local variable is necessary, because it emits `KPRI`
+-- bytecode, with which the next `KPRI` bytecode will be merged.
 local _
 for _ in (nil):foo() do end
 ]])
 
-test:ok(res_f, 'chunk loaded sucsessfully')
+test:ok(res_f, 'chunk loaded successfully')
 
 local res, err = pcall(res_f)
 
+-- Check consistency with PUC Rio Lua 5.1 behaviour.
 test:ok(not res, 'loaded function not executed')
 test:like(err, 'attempt to index a nil value', 'correct error message')
 
===================================================================

Branch is force-pushed.

> 
> 
> > +test:like(err, 'attempt to index a nil value', 'correct error message')
> > +
> > +test:done(true)

-- 
Best regards,
Sergey Kaplun

Re: [Tarantool-patches] [PATCH luajit] Fix predict_next() in parser.

[Sergey Bronnikov via Tarantool-patches]

Hi,


On 8/22/23 18:17, Sergey Kaplun wrote:

<snipped>


>>> +
>>> +local res, err = pcall(res_f)
>>> +
>>> +test:ok(not res, 'loaded function not executed')
>> it is not clear for me what for do you need checking result code. I
>> would omit it.
>>
>> Feel free to ignore.
> Added the following comment to avoid confusing (see the whole iterative
> patch below):
>
> ===================================================================
> diff --git a/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> index 63998d8c..fed3ff6c 100644
> --- a/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> +++ b/test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> @@ -3,10 +3,6 @@ local test = tap.test('lj-1033-fix-parsing-predict-next')
>   
>   test:plan(3)
>   
> -local res_f = loadstring([[
> --- This local variable is necessary, because it emits `KPRI`
> --- bytecode, with which the next `KPRI` bytecode will be merged.
> ---
>   -- The resulting bytecode is the following:
>   --
>   -- 0001    KNIL     0   1
> @@ -16,14 +12,18 @@ local res_f = loadstring([[
>   --
>   -- This MOV doesn't use any variable value from the stack, so the
>   -- attempt to get the name in `predict_next() leads to the crash.
> +local res_f = loadstring([[
> +-- This local variable is necessary, because it emits `KPRI`
> +-- bytecode, with which the next `KPRI` bytecode will be merged.
>   local _
>   for _ in (nil):foo() do end
>   ]])
>   
> -test:ok(res_f, 'chunk loaded sucsessfully')
> +test:ok(res_f, 'chunk loaded successfully')
>   
>   local res, err = pcall(res_f)
>   
> +-- Check consistency with PUC Rio Lua 5.1 behaviour.
>   test:ok(not res, 'loaded function not executed')
>   test:like(err, 'attempt to index a nil value', 'correct error message')
>   
> ===================================================================
>
> Branch is force-pushed.
>
Thanks! LGTM now.


>>
>>> +test:like(err, 'attempt to index a nil value', 'correct error message')
>>> +
>>> +test:done(true)

Re: [Tarantool-patches] [PATCH luajit] Fix predict_next() in parser.

[Igor Munkin via Tarantool-patches]

Sergey,

I've checked the patchset into all long-term branches in
tarantool/luajit and bumped a new version in master, release/2.11 and
release/2.10.

On 15.08.23, Sergey Kaplun via Tarantool-patches wrote:
> From: Mike Pall <mike>
> 
> Reported by Sergey Kaplun.
> 
> (cherry-picked from commit caf7cbc57c945f7b68871ad72abafb2b6e6fb7f5)
> 
> Assume, we have the following Lua code:
> | local _
> | for _ in (nil):foo() do end
> 
> The first part of the bytecode emitted for it is the following:
> | 0001    KNIL     0   1
> | 0002    MOV      2   1
> | 0003    TGETS    1   1   0  ; "foo"
> | 0004    CALL     1   4   2
> 
> The `0001 KNIL` is a result of merging two `KPRI` instructions: one for
> the local variable, one for the slot with `nil` object. During parsing in
> `predict_next()` the second `MOV` bytecode is examined to set `pairs` or
> `next` local variable. But, as far as it moves `nil` value, that isn't
> an actual variable, so it has no the name this leads to the crash.
> 
> This patch adds the check to be sure that `RD` in the `MOV` bytecode is
> an actual variable.
> 
> Sergey Kaplun:
> * added the description and the test for the problem
> 
> Part of tarantool/tarantool#8825
> ---
> 
> Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1033-fix-parsing-predict-next
> PR: https://github.com/tarantool/tarantool/pull/8987
> Related issues:
> * https://github.com/LuaJIT/LuaJIT/issues/1033
> * https://github.com/tarantool/tarantool/issues/8825
> 
>  src/lj_parse.c                                |  1 +
>  .../lj-1033-fix-parsing-predict-next.test.lua | 30 +++++++++++++++++++
>  2 files changed, 31 insertions(+)
>  create mode 100644 test/tarantool-tests/lj-1033-fix-parsing-predict-next.test.lua
> 

<snipped>

> -- 
> 2.41.0
> 

-- 
Best regards,
IM