Re: [Tarantool-patches] [PATCH luajit] x64: Properly fix __call metamethod return dispatch.

[Igor Munkin via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Sergey,

Thanks for the patch! LGTM as obvious, except the single nit regarding
the commit message.

On 07.11.23, Sergey Kaplun wrote:
> From: Mike Pall <mike>
> 
> Reported by Sergey Kaplun.
> 
> (cherry-picked from commit d133d67c881f363f0b5584ebd21a965eb3435aa1)
> 
> This patch is the follow-up for the commit
> 1672bdc0ffbee9f32fadb6943909d6af7eb9a7b1 ("x64: Fix __call metamethod
> return dispatch."). This patch uses the incorrect macro x64 (which is

I don't get which one of the aforementioned patches is "this": *this*
one fixing the issue, or *that* one, that doesn't.

> undefined in dasm) instead of X64. `KBASE` (r15d) is still compared
> against `BASE` (edx) instead of `KBASEa` (r15) against rdx.
> 
> This patch fixes the typo, so the correct registers are chosen.

Side note: I hope it definitely is, but we still have no tests for it.

> 
> Sergey Kaplun:
> * added the description for the problem
> 
> Part of tarantool/tarantool#9145
> ---
> 
> The test is omitted for the same reason as it was omitted in the 1672bdc
> commit: it is too hard (or even impossible) to create the test case.
> 
> Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1110-x64-return-dispatch
> Tarantool PR: https://github.com/tarantool/tarantool/pull/9335
> Relate issues and PRs:
> * https://github.com/LuaJIT/LuaJIT/pull/636
> * https://github.com/LuaJIT/LuaJIT/issues/1110
> * https://github.com/tarantool/tarantool/issues/9145
> 
>  src/vm_x86.dasc | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/vm_x86.dasc b/src/vm_x86.dasc
> index 9fa9a3f7..6a353796 100644
> --- a/src/vm_x86.dasc
> +++ b/src/vm_x86.dasc
> @@ -1451,7 +1451,7 @@ static void build_subroutines(BuildCtx *ctx)
>    |  mov LFUNC:RB, [RA-8]
>    |  add NARGS:RD, 1
>    |  // This is fragile. L->base must not move, KBASE must always be defined.
> -  |.if x64
> +  |.if X64

Bonjour.

>    |  cmp KBASEa, rdx			// Continue with CALLT if flag set.
>    |.else
>    |  cmp KBASE, BASE			// Continue with CALLT if flag set.
> -- 
> 2.42.0
> 

-- 
Best regards,
IM