Re: [PATCH] be2net: fix adapter->big_page_size miscaculation

From: David Miller <davem@davemloft.net>
To: cai@lca.pw
Cc: 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
Subject: Re: [PATCH] be2net: fix adapter->big_page_size miscaculation
Date: Fri, 12 Jul 2019 17:50:38 -0700 (PDT)	[thread overview]
Message-ID: <20190712.175038.755685144649934618.davem@davemloft.net> (raw)
In-Reply-To: <EFD25845-097A-46B1-9C1A-02458883E4DA@lca.pw>

From: Qian Cai <cai@lca.pw>
Date: Fri, 12 Jul 2019 20:27:09 -0400

> Actually, GCC would consider it a const with -O2 optimized level because it found that it was never modified and it does not understand it is a module parameter. Considering the following code.
> 
> # cat const.c 
> #include <stdio.h>
> 
> static int a = 1;
> 
> int main(void)
> {
> 	if (__builtin_constant_p(a))
> 		printf("a is a const.\n");
> 
> 	return 0;
> }
> 
> # gcc -O2 const.c -o const

That's not a complete test case, and with a proper test case that
shows the externalization of the address of &a done by the module
parameter macros, gcc should not make this optimization or we should
define the module parameter macros in a way that makes this properly
clear to the compiler.

It makes no sense to hack around this locally in drivers and other
modules.

Thank you.