Re: [Tarantool-patches] [PATCH luajit] test: adapt test checking reversed function

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

Hi, Maxim!

Thanks for the patch!

Please consider my comments below.

On 30.09.21, Maxim Kokryashkin wrote:
> The first fiber in Tarantool has only 512Kb of the stack which is not enough to
> handle such a deep call chain.
> The test is adapted to Tarantool by decreasing the string length.
> 
> Closes tarantool/tarantool#5782
> Part of tarantool/tarantool#5845
> Part of tarantool/tarantool#4473

Looks like it should be 5870 instead 4473. Also, 5845 is already
closed.

> ---

Please show the Tarantool branch as well, to show that problem is gone.

> GitHub branch: https://github.com/tarantool/luajit/tree/fckxorg/gh-5782-adapt-deep-nest-gsub-PUC-Rio
> Issue: https://github.com/tarantool/tarantool/issues/5782
> 
>  test/PUC-Rio-Lua-5.1-tests/pm.lua | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/test/PUC-Rio-Lua-5.1-tests/pm.lua b/test/PUC-Rio-Lua-5.1-tests/pm.lua
> index e364ff9d..7da3ef4a 100644
> --- a/test/PUC-Rio-Lua-5.1-tests/pm.lua
> +++ b/test/PUC-Rio-Lua-5.1-tests/pm.lua
> @@ -206,12 +206,11 @@ function rev (s)
>    return string.gsub(s, "(.)(.+)", function (c,s1) return rev(s1)..c end)
>  end
>  
> -local x = string.rep('012345', 10)
> --- FIXME: The first Tarantool's fiber has only 512Kb of stack.
> --- It is not enough for this recursive call.
> +-- This test is adapted to match the stack size (512Kb) of the first fiber in
> +-- Tarantool.
>  -- See also https://github.com/tarantool/tarantool/issues/5782.
> --- The test is disabled for Tarantool binary.
> --- assert(rev(rev(x)) == x)
> +local x = string.rep('01234', 10)
> +assert(rev(rev(x)) == x)

The patch is looks OK to me, but the main problem is still here:
LuaJIT is badly managing C stack overflow. The same chunk rases an error
for Lua 5.1, but crashes for LuaJIT.

| $ luajit -e 'local function rev (s) return string.gsub(s, "(.)(.+)", function (c,s1) return rev(s1)..c end) end local x = string.rep("0", 1000) rev(x)'
| Segmentation fault

| $ lua    -e 'local function rev (s) return string.gsub(s, "(.)(.+)", function (c,s1) return rev(s1)..c end) end local x = string.rep("0", 1000) rev(x)'
| lua: C stack overflow
| stack traceback:
|         [C]: in function 'gsub'
|         (command line):1: in function 'rev'
|         (command line):1: in function <(command line):1>
|         [C]: in function 'gsub'
|         (command line):1: in function 'rev'
|         (command line):1: in function <(command line):1>
|         [C]: in function 'gsub'
|         (command line):1: in function 'rev'
|         (command line):1: in function <(command line):1>
|         [C]: in function 'gsub'
|         ...
|         [C]: in function 'gsub'
|         (command line):1: in function 'rev'
|         (command line):1: in function <(command line):1>
|         [C]: in function 'gsub'
|         (command line):1: in function 'rev'
|         (command line):1: in function <(command line):1>
|         [C]: in function 'gsub'
|         (command line):1: in function 'rev'
|         (command line):1: in main chunk
|         [C]: ?

So I suppose it is strange to add test that tests nothing.

Thoughts?

>  
>  
>  -- gsub with tables
> -- 
> 2.33.0
> 

-- 
Best regards,
Sergey Kaplun