linux-kernel - Re: [PATCH 2/2] s390/fpu: make use of _

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Date: Mon, 5 Feb 2024 17:35:29 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Kees Cook <keescook@...omium.org>
Cc: Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>
Subject: Re: [PATCH 2/2] s390/fpu: make use of __uninitialized macro

On Mon, Feb 05, 2024 at 08:26:32AM -0800, Kees Cook wrote:
> > +#define DECLARE_KERNEL_FPU_ONSTACK(name)	\
> > +	struct kernel_fpu name __uninitialized
> 
> Are there cases when struct kernel_fpu should be initialized? e.g.
> should the attribute just be added to the struct definition instead of
> marking each use?

I tried that, but failed:

/arch/s390/include/asm/fpu/types.h:36:3: warning: '__uninitialized__' attribute only applies to local variables [-Wignored-attributes]
   36 | } __uninitialized;
      |   ^
/include/linux/compiler_attributes.h:343:42: note: expanded from macro '__uninitialized'
  343 | # define __uninitialized                __attribute__((__uninitialized__))
      |                                                        ^

That's why I came up with this macro. I'd prefer to have this added only to
the struct definition, but looks like this is not possible (or I just can't
figure out who to do that).