linux-kernel - Re: [PATCH v19 008/130] x86/tdx: Warning with 32bit build shift-count-overflow

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Date: Wed, 6 Mar 2024 14:17:28 -0800
From: Isaku Yamahata <isaku.yamahata@...ux.intel.com>
To: "Huang, Kai" <kai.huang@...el.com>
Cc: Isaku Yamahata <isaku.yamahata@...ux.intel.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	isaku.yamahata@...el.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>, chen.bo@...el.com,
	hang.yuan@...el.com, tina.zhang@...el.com
Subject: Re: [PATCH v19 008/130] x86/tdx: Warning with 32bit build
 shift-count-overflow

On Wed, Mar 06, 2024 at 10:35:43AM +1300,
"Huang, Kai" <kai.huang@...el.com> wrote:

> 
> 
> On 5/03/2024 9:12 pm, Isaku Yamahata wrote:
> > On Fri, Mar 01, 2024 at 01:36:43PM +0200,
> > "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> wrote:
> > 
> > > On Thu, Feb 29, 2024 at 11:49:13AM +1300, Huang, Kai wrote:
> > > > 
> > > > 
> > > > On 26/02/2024 9:25 pm, isaku.yamahata@...el.com wrote:
> > > > > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > > > > 
> > > > > This patch fixes the following warnings.
> > > > > 
> > > > >      In file included from arch/x86/kernel/asm-offsets.c:22:
> > > > >      arch/x86/include/asm/tdx.h:92:87: warning: shift count >= width of type [-Wshift-count-overflow]
> > > > >      arch/x86/include/asm/tdx.h:20:21: note: expanded from macro 'TDX_ERROR'
> > > > >      #define TDX_ERROR                       _BITUL(63)
> > > > > 
> > > > >                                              ^~~~~~~~~~
> > > > > 
> > > 
> > > I think you trim the warning message. I don't see the actual user of the
> > > define. Define itself will not generate the warning. You need to actually
> > > use it outside of preprocessor. I don't understand who would use it in
> > > 32-bit code. Maybe fixing it this way masking other issue.
> > > 
> > > That said, I don't object the change itself. We just need to understand
> > > the context more.
> > 
> > v18 used it as stub function. v19 dropped it as the stub was not needed.
> 
> Sorry I literally don't understand what you are talking about here.
> 
> Please just clarify (at least):
> 
>  - Does this problem exist in upstream code?

No.

>  - If it does, what is the root cause, and how to reproduce?

v18 had a problem because it has stub function. v19 doesn't have problem because
it deleted the stub function.
-- 
Isaku Yamahata <isaku.yamahata@...ux.intel.com>