linux-kernel - Re: [PATCH] [v2] ethtool: reduce stack usage with clang

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Message-Id: <20190307.094600.334828809875646248.davem@davemloft.net>
Date:   Thu, 07 Mar 2019 09:46:00 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     arnd@...db.de
Cc:     f.fainelli@...il.com, jakub.kicinski@...ronome.com,
        jiri@...lanox.com, wang6495@....edu, mkubecek@...e.cz,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [v2] ethtool: reduce stack usage with clang

From: Arnd Bergmann <arnd@...db.de>
Date: Thu,  7 Mar 2019 16:58:35 +0100

> clang inlines the dev_ethtool() more aggressively than gcc does, leading
> to a larger amount of used stack space:
> 
> net/core/ethtool.c:2536:24: error: stack frame size of 1216 bytes in function 'dev_ethtool' [-Werror,-Wframe-larger-than=]
> 
> Marking the sub-functions that require the most stack space as
> noinline_for_stack gives us reasonable behavior on all compilers.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> v2: don't annotate dev_ethtool itself, as pointed out by Michal Kubecek

I'll apply this, but as Michal said this is just papering over the problem,
the aggregate stack allocation is still the same and very large.