Re: [Tarantool-patches] [PATCH luajit] FFI: Add tonumber() specialization for failed conversions.

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

Hi, Sergos!

On 21.09.22, sergos wrote:
> Hi!
> 
> I see four ‘ok’s as a result of run. 
> See the full output for the run with dump() below:
> 
> 
> s.ostanevich@s-ostanevich2:~/workspaces/t.sergos/third_party/luajit/test/tarantool-tests % ../../../../build-debug/src/tarantool -e 'require"jit.dump".start("ib")' lj-408-tonumber-cdata-record.test.lua
> 
> TAP version 13
> 1..4
> ---- TRACE 1 start lj-408-tonumber-cdata-record.test.lua:17
> 0001  GGET     1   0      ; "tonumber"
> 0002  MOV      3   0
> 0003  CALL     1   2   2
> 0000  . FUNCC               ; tonumber
> 0004  RET1     1   2
> ---- TRACE 1 IR
> 0001    fun SLOAD  #0    R
> 0002    tab FLOAD  0001  func.env
> 0003    int FLOAD  0002  tab.hmask
> 0004 >  int EQ     0003  +63 
> 0005    p64 FLOAD  0002  tab.node
> 0006 >  p64 HREFK  0005  "tonumber" @8
> 0007 >  fun HLOAD  0006
> 0008 >  cdt SLOAD  #2    T
> 0009 >  fun EQ     0007  tonumber
> ---- TRACE 1 stop -> return

Gotcha!
It's a funny thing:
This is happening due to GC64 mode on x86_x64.

There is an invalid type check for SLOAD IR with the following emitted
mcode:

| 55557f6bffc9  mov rdi, [rdx+0x4]
| 55557f6bffcd  sar rdi, 0x2f
| 55557f6bffd1  cmp edi, -0x0b
| 55557f6bffd4  jnz 0x55557f6b0010        ->0

This 0x4 addiction is crucial:
We got the invalid irtype value to compare (due wrong addressing) -- so
the assertion guard is always failed and we always exit from the trace.
This is why we fallback into the interpreter and the test is passed.

In LuaJIT upstream this issue fixed via the following commit:
https://github.com/LuaJIT/LuaJIT/commit/05fbdf56

See also https://github.com/LuaJIT/LuaJIT/pull/350

<snipped>

> 

-- 
Best regards,
Sergey Kaplun