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 Fri,  4 Dec 2020 19:24:44 +0300 (MSK)
Date: Fri, 4 Dec 2020 19:24:41 +0300
From: Igor Munkin <imun@tarantool.org>
Message-ID: <20201204162441.GC5396@tarantool.org>
References: <a0b974caa57b980eddaf94ce26f2c7968855e95b.1607088022.git.imun@tarantool.org>
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In-Reply-To: <a0b974caa57b980eddaf94ce26f2c7968855e95b.1607088022.git.imun@tarantool.org>
Subject: Re: [Tarantool-patches] [PATCH luajit] x64: Fix __call metamethod
	return dispatch.
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To: "Alexander V. Tikhonov" <avtikhon@tarantool.org>
Cc: tarantool-patches@dev.tarantool.org

Sasha,

Could you please confirm whether CI is OK?

On 04.12.20, Igor Munkin wrote:
> From: Mike Pall <mike>
> 
> After linking new cframe to the chain KBASEa still stores the address of
> the previous one. If the execution proceeds to <lj_vmeta_call> KBASE
> value (i.e. low 32 bits of the stored address) might be equal to the
> current BASE address value so the execution takes the invalid path. Such
> address clashing occurs only on x86_64 platform with disabled LJ_GC64,
> so 64-bit registers have to be compared in x64 build.
> 
> NB: Though there is only 32-bit load to restore BASE value prior to the
> comparison, the high 32 bits of RDX are reset to zeros, according to x86
> long mode semantics.
> 
> Igor Munkin:
> * backported the original patch to tarantool/luajit repo
> * extended the original commit message with the rationale
> 
> For more info and explanation see LuaJIT/LuaJIT#636.
> 
> Relates to tarantool/tarantool#4518
> Relates to tarantool/tarantool#4649
> 
> Signed-off-by: Igor Munkin <imun@tarantool.org>
> ---
> 
> Issues:
> * https://github.com/tarantool/tarantool/issues/4518
> * https://github.com/tarantool/tarantool/issues/4649
> Branch:
> * https://github.com/tarantool/luajit/tree/imun/gh-4518-cmp-64-bit-regs-in-vmeta-call
> 
> CI is kinda green, considering C6 EOL and the corresponding failures:
> * https://gitlab.com/tarantool/tarantool/-/pipelines/225349795
> 
> @ChangeLog:
> * Fixed address clashing occurring while __call metamethod dispatching
>   (gh-4518, gh-4649).
> 
> Unfortunately, there is neither test nor reproducer for this failure, so
> we'll know that the patch works only on production installations.
> 

<snipped>

> 

-- 
Best regards,
IM