linux-kernel - Re: [PATCH] lib/Kconfig.debug: disable FRAME

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Message-ID: <a9237e7a-e08c-4904-b84a-f6198333a78c@amd.com>
Date:   Thu, 19 Oct 2023 16:17:26 -0400
From:   Hamza Mahfooz <hamza.mahfooz@....com>
To:     Nathan Chancellor <nathan@...nel.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-kernel@...r.kernel.org,
        Rodrigo Siqueira <rodrigo.siqueira@....com>,
        Harry Wentland <harry.wentland@....com>,
        Alex Deucher <alexander.deucher@....com>,
        stable@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Nick Terrell <terrelln@...com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        Li Hua <hucool.lihua@...wei.com>, Rae Moar <rmoar@...gle.com>,
        rust-for-linux@...r.kernel.org, bpf@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] lib/Kconfig.debug: disable FRAME_WARN for kasan and kcsan

On 10/19/23 11:56, Nathan Chancellor wrote:
> On Thu, Oct 19, 2023 at 02:53:01PM +0200, Arnd Bergmann wrote:
>> On Thu, Oct 19, 2023, at 12:04, Alexander Potapenko wrote:
>>> So the remaining option would be to just increase the frame size every
>>> time a new function surpasses the limit.
>>
>> That is clearly not an option, though we could try to
>> add Kconfig dependencies that avoid the known bad combinations,
>> such as annotating the AMD GPU driver as
>>
>>        depends on (CC_IS_GCC || CLANG_VERSION >=180000) || !(KASAN || KCSAN)
> 
> This would effectively disable the AMDGPU driver for allmodconfig, which
> is somewhat unfortunate as it is an easy testing target.
> 
> Taking a step back, this is all being done because of a couple of
> warnings in the AMDGPU code. If fixing those in the source is too much
> effort (I did note [1] that GCC is at the current limit for that file
> even with Rodrigo's series applied [2]), couldn't we just take the
> existing workaround that this Makefile has for this file and its high
> stack usage and just extend it slightly for clang?

I personally don't mind fixing these issues in the driver, but the fact
that they the creep back every time a new major version of Clang rolls
out (that has been true for the past couple of years at the very
least), makes it rather annoying to deal with.

> 
> diff --git a/drivers/gpu/drm/amd/display/dc/dml2/Makefile b/drivers/gpu/drm/amd/display/dc/dml2/Makefile
> index 66431525f2a0..fd49e3526c0d 100644
> --- a/drivers/gpu/drm/amd/display/dc/dml2/Makefile
> +++ b/drivers/gpu/drm/amd/display/dc/dml2/Makefile
> @@ -58,7 +58,7 @@ endif
>   endif
>   
>   ifneq ($(CONFIG_FRAME_WARN),0)
> -frame_warn_flag := -Wframe-larger-than=2048
> +frame_warn_flag := -Wframe-larger-than=$(if $(CONFIG_CC_IS_CLANG),3072,2048)
>   endif
>   
>   CFLAGS_$(AMDDALPATH)/dc/dml2/display_mode_core.o := $(dml2_ccflags) $(frame_warn_flag)
> 
> That would address the immediate concern of the warning breaking builds
> with CONFIG_WERROR=y while not raising the limit for other files in the
> kernel (just this one file in AMDGPU) and avoiding disabling the whole
> driver. The number could be lower, I think ~2500 bytes is the most usage
> I see with Rodrigo's series applied, so maybe 2800 would be a decent
> limit? Once there is a fix in the compiler, this expression could be
> changed to use clang-min-version or something of that sort.
> 
> [1]: https://lore.kernel.org/20231017172231.GA2348194@dev-arch.thelio-3990X/
> [2]: https://lore.kernel.org/20231016142031.241912-1-Rodrigo.Siqueira@amd.com/
> 
> Cheers,
> Nathan
-- 
Hamza