linux-kernel - sparse bad constant expression caused by 7322dd755e7d ("byteswap: try to avoid __builtin_constant

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Date:	Tue, 21 Jun 2016 23:14:43 +0000
From:	"Keller, Jacob E" <jacob.e.keller@...el.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...nel.org>,
	"Josh Poimboeuf" <jpoimboe@...hat.com>
Subject: sparse bad constant expression caused by 7322dd755e7d ("byteswap:
 try to avoid __builtin_constant_p gcc bug", 2016-05-05)

Hi,

I recently ran into a sparse error when running sparse on Intel's i40e kernel driver against v4.7-rc3.

  CC [M]  drivers/net/ethernet/intel/i40e/i40e_nvm.o
include/linux/sctp.h:172:51: error: bad constant expression
include/linux/sctp.h:174:51: error: bad constant expression
include/linux/sctp.h:172:51: error: bad constant expression
include/linux/sctp.h:174:51: error: bad constant expression
include/linux/sctp.h:175:51: error: bad constant expression
include/linux/sctp.h:176:51: error: bad constant expression
include/linux/sctp.h:177:51: error: bad constant expression
include/linux/sctp.h:178:51: error: bad constant expression

And similar. I ran a bisect and determined the offending commit was 7322dd755e7d ("byteswap: try to avoid __builtin_constant_p gcc bug", 2016-05-05)

I am not sure if this is a regression in sparse, a real issue, or something else?

Thanks,
Jake