Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-ID: <1563572871.11067.2.camel@lca.pw>
Subject: Re: [PATCH] be2net: fix adapter->big_page_size miscaculation
From:   Qian Cai <cai@lca.pw>
To:     David Miller <davem@davemloft.net>
Cc:     morbo@google.com, ndesaulniers@google.com, jyknight@google.com,
        sathya.perla@broadcom.com, ajit.khaparde@broadcom.com,
        sriharsha.basavapatna@broadcom.com, somnath.kotur@broadcom.com,
        arnd@arndb.de, dhowells@redhat.com, hpa@zytor.com,
        netdev@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-kernel@vger.kernel.org, natechancellor@gmail.com
Date:   Fri, 19 Jul 2019 17:47:51 -0400
In-Reply-To: <20190718.162928.124906203979938369.davem@davemloft.net>
References: <CAKwvOdkCfqfpJYYX+iu2nLCUUkeDorDdVP3e7koB9NYsRwgCNw@mail.gmail.com>
         <CAGG=3QUvdwJs1wW1w+5Mord-qFLa=_WkjTsiZuwGfcjkoEJGNQ@mail.gmail.com>
         <75B428FC-734C-4B15-B1A7-A3FC5F9F2FE5@lca.pw>
         <20190718.162928.124906203979938369.davem@davemloft.net>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, 2019-07-18 at 16:29 -0700, David Miller wrote:
> From: Qian Cai <cai@lca.pw>
> Date: Thu, 18 Jul 2019 19:26:47 -0400
> 
> > 
> > 
> >> On Jul 18, 2019, at 5:21 PM, Bill Wendling <morbo@google.com> wrote:
> >> 
> >> [My previous response was marked as spam...]
> >> 
> >> Top-of-tree clang says that it's const:
> >> 
> >> $ gcc a.c -O2 && ./a.out
> >> a is a const.
> >> 
> >> $ clang a.c -O2 && ./a.out
> >> a is a const.
> > 
> > 
> > I used clang-7.0.1. So, this is getting worse where both GCC and clang will
> start to suffer the
> > same problem.
> 
> Then rewrite the module parameter macros such that the non-constness
> is evident to all compilers regardless of version.
> 
> That is the place to fix this, otherwise we will just be adding hacks
> all over the place rather than in just one spot.

The problem is that when the compiler is compiling be_main.o, it has no
knowledge about what is going to happen in load_module().  The compiler can only
see that a "const struct kernel_param_ops" "__param_ops_rx_frag_size" at the
time with

__param_ops_rx_frag_size.arg = &rx_frag_size

but only in load_module()->parse_args()->parse_one()->param_set_ushort(), it
changes "__param_ops_rx_frag_size.arg" which in-turn changes the value
of "rx_frag_size".