linux-kernel - Re: Sparse warnings on GENMASK + arm32

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Date:   Wed, 26 Jul 2017 15:46:17 +0200
From:   Luc Van Oostenryck <luc.vanoostenryck@...il.com>
To:     Lance Richardson <lrichard@...hat.com>
Cc:     Stephen Boyd <sboyd@...eaurora.org>, linux-sparse@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Sparse warnings on GENMASK + arm32

On Wed, Jul 26, 2017 at 09:33:01AM -0400, Lance Richardson wrote:
> > From: "Stephen Boyd" <sboyd@...eaurora.org>
> > I see sparse warning when I check a clk driver file in the kernel
> > on a 32-bit ARM build.
> > 
> > drivers/clk/sunxi/clk-sun6i-ar100.c:65:20: warning: cast truncates bits from
> > constant value (3ffffffff becomes ffffffff)
> 
> Hmm, it seems sparse is incorrectly taking ~0UL to be a 64-bit value
> while BITS_PER_LONG is (correctly) evaluated to be 32.
> 
> #define GENMASK(h, l) \
> 	(((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))

It's the kernel CHECKFLAGS that should be using -m32/-m64 if built
on a machine with a different wordsize tht the arch.

I sent earlier a patch for ARM, I just forgot to CC the mailing list here.

-- Luc