linux-kernel - Re: [PATCH] be2net: fix adapter->big_page

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Message-ID: <1563572871.11067.2.camel@lca.pw>
Date:   Fri, 19 Jul 2019 17:47:51 -0400
From:   Qian Cai <cai@....pw>
To:     David Miller <davem@...emloft.net>
Cc:     morbo@...gle.com, ndesaulniers@...gle.com, jyknight@...gle.com,
        sathya.perla@...adcom.com, ajit.khaparde@...adcom.com,
        sriharsha.basavapatna@...adcom.com, somnath.kotur@...adcom.com,
        arnd@...db.de, dhowells@...hat.com, hpa@...or.com,
        netdev@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, natechancellor@...il.com
Subject: Re: [PATCH] be2net: fix adapter->big_page_size miscaculation

On Thu, 2019-07-18 at 16:29 -0700, David Miller wrote:
> From: Qian Cai <cai@....pw>
> Date: Thu, 18 Jul 2019 19:26:47 -0400
> 
> > 
> > 
> >> On Jul 18, 2019, at 5:21 PM, Bill Wendling <morbo@...gle.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".