linux-kernel - Re: [tip:x86/cpu 2/3] arch/x86/kernel/alternative.c:96:10: warning: Undefined behaviour, pointer arithmetic 'x86nops+10' is out of bounds.

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Date:   Tue, 16 Mar 2021 10:01:21 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     kernel test robot <lkp@...el.com>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [tip:x86/cpu 2/3] arch/x86/kernel/alternative.c:96:10: warning:
 Undefined behaviour, pointer arithmetic 'x86nops+10' is out of bounds.

On Tue, Mar 16, 2021 at 09:27:03AM +0100, Borislav Petkov wrote:
> Yet another useless report!
> 
> On Tue, Mar 16, 2021 at 07:50:10AM +0800, kernel test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/cpu
> > head:   301cddc21a157a3072d789a3097857202e550a24
> > commit: a89dfde3dc3c2dbf56910af75e2d8b11ec5308f6 [2/3] x86: Remove dynamic NOP selection
> > compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
> > 
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@...el.com>
> > 
> > 
> > cppcheck possible warnings: (new ones prefixed by >>, may not real problems)
> 
> What's cppcheck?
> 
> That?
> 
> Description-en: tool for static C/C++ code analysis (CLI)
>  Cppcheck is a command-line tool that tries to detect bugs that your
> 
> 
> > >> arch/x86/kernel/alternative.c:96:10: warning: Undefined behaviour, pointer arithmetic 'x86nops+10' is out of bounds. [pointerOutOfBounds]
> >     x86nops + 1 + 2 + 3 + 4,
> >             ^
> >    arch/x86/kernel/alternative.c:97:10: warning: Undefined behaviour, pointer arithmetic 'x86nops+15' is out of bounds. [pointerOutOfBounds]
> >     x86nops + 1 + 2 + 3 + 4 + 5,
> >             ^
> >    arch/x86/kernel/alternative.c:98:10: warning: Undefined behaviour, pointer arithmetic 'x86nops+21' is out of bounds. [pointerOutOfBounds]
> >     x86nops + 1 + 2 + 3 + 4 + 5 + 6,
> >             ^
> >    arch/x86/kernel/alternative.c:99:10: warning: Undefined behaviour, pointer arithmetic 'x86nops+28' is out of bounds. [pointerOutOfBounds]
> >     x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
> >             ^
> > >> arch/x86/kernel/ftrace.c:304:7: warning: union member 'ftrace_op_code_union::code' is never used. [unusedStructMember]
> >     char code[OP_REF_SIZE];
> >          ^
> 
> How do you trigger this?
> 
> /me ignores it until there's some info on how those things can be
> reproduced.

Just ignore, cppcheck is a load of crap. I don't know why they bother
running it.