linux-kernel - Re: [PATCH] drm: a6xx: avoid excessive stack usage

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Message-ID: <k42wmgziqia6balqsrfualbg73giesjxxtyaldkxsrdxkro2li@6neybqsu27me>
Date: Sat, 19 Oct 2024 16:14:13 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Akhil P Oommen <quic_akhilpo@...cinc.com>
Cc: Arnd Bergmann <arnd@...nel.org>, Rob Clark <robdclark@...il.com>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Nathan Chancellor <nathan@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Sean Paul <sean@...rly.run>, 
	Konrad Dybcio <konradybcio@...nel.org>, Marijn Suijten <marijn.suijten@...ainline.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] drm: a6xx: avoid excessive stack usage

On Sat, Oct 19, 2024 at 03:01:46PM +0530, Akhil P Oommen wrote:
> On Fri, Oct 18, 2024 at 03:11:38PM +0000, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> > 
> > Clang-19 and above sometimes end up with multiple copies of the large
> > a6xx_hfi_msg_bw_table structure on the stack. The problem is that
> > a6xx_hfi_send_bw_table() calls a number of device specific functions to
> > fill the structure, but these create another copy of the structure on
> > the stack which gets copied to the first.
> > 
> > If the functions get inlined, that busts the warning limit:
> > 
> > drivers/gpu/drm/msm/adreno/a6xx_hfi.c:631:12: error: stack frame size (1032) exceeds limit (1024) in 'a6xx_hfi_send_bw_table' [-Werror,-Wframe-larger-than]
> 
> Why does this warning says that the limit is 1024? 1024 bytes is too small, isn't it?

Kernel stacks are expected to be space limited, so 1024 is a logical
limit for a single function.


-- 
With best wishes
Dmitry