Re: [Tarantool-patches] [PATCH luajit 3/4] ARM64: Fix xpcall() error case.

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

Hi!

Thanks for the patch!

Some comments facelift, otherwise LGTM.

Sergos


> On 24 May 2021, at 16:27, Sergey Kaplun <skaplun@tarantool.org> wrote:
> 
> From: Mike Pall <mike>	
> 
> Thanks to Stefan Pejic.
> 
> (cherry picked from commit 33082a6f4778aa152f6a4a684a7fe79436f1ecb6)
> 
> Premature incrementing VM's BASE register before switch to fff_fallback
	   increment of
> handler during processing `xpcall()` fast function leads to incorrect
> L->base value in case, when `xpcall()` calls without a second argument
					is called
> or if it equals nil (see <301-basic.t> test in lua-Harness test suite).
> While further error processing it leads to crash, due to stack
> inconsistency.

Please, mention explicitly if this test is the one for the patch.

> 
> This patch moves BASE incrementing after possible switching to
			increment          the switch (mentioned in first line)
> fallback handler.
the (aforementioned) 
> 
> Sergey Kaplun:
> * added the description for the problem
> 
> Part of tarantool/tarantool#6093
> Part of tarantool/tarantool#5629
> ---
> src/vm_arm64.dasc | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/vm_arm64.dasc b/src/vm_arm64.dasc
> index 6bf59509..e16a77ab 100644
> --- a/src/vm_arm64.dasc
> +++ b/src/vm_arm64.dasc
> @@ -1186,12 +1186,12 @@ static void build_subroutines(BuildCtx *ctx)
>   |   subs NARGS8:RC, NARGS8:RC, #16
>   |   blo ->fff_fallback
>   |    mov RB, BASE
> -  |    add BASE, BASE, #24
>   |     asr ITYPE, CARG2, #47
>   |  ubfx TMP0w, TMP0w, #HOOK_ACTIVE_SHIFT, #1
>   |     cmn ITYPE, #-LJ_TFUNC
>   |  add PC, TMP0, #24+FRAME_PCALL
>   |     bne ->fff_fallback		// Traceback must be a function.
> +  |    add BASE, BASE, #24
>   |     stp CARG2, CARG1, [RB]		// Swap function and traceback.
>   |   cbz NARGS8:RC, ->vm_call_dispatch
>   |  b <1
> -- 
> 2.31.0
>