Re: [PATCH 1/1] x86/boot: clear some fields explicitly

From: John Hubbard <jhubbard@nvidia.com>
To: <hpa@zytor.com>, <john.hubbard@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	<x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/1] x86/boot: clear some fields explicitly
Date: Wed, 24 Jul 2019 23:49:22 -0700	[thread overview]
Message-ID: <f83947fe-8a80-8693-56bd-76cb6f37317e@nvidia.com> (raw)
In-Reply-To: <B7DC31CA-E378-445A-A937-1B99490C77B4@zytor.com>

On 7/24/19 7:12 PM, hpa@zytor.com wrote:
> On July 24, 2019 4:15:28 PM PDT, john.hubbard@gmail.com wrote:
>> From: John Hubbard <jhubbard@nvidia.com>
...
>> +		boot_params->ext_ramdisk_image = 0;
>> +		boot_params->ext_ramdisk_size = 0;
>> +		boot_params->ext_cmd_line_ptr = 0;
>> +
>> +		memset(&boot_params->_pad4, 0, sizeof(boot_params->_pad4));
>> 		memset(&boot_params->_pad7[0], 0,
>> 		       (char *)&boot_params->edd_mbr_sig_buffer[0] -
>> 			(char *)&boot_params->_pad7[0]);
> 
> The problem with this is that it will break silently when changes are made to this structure.
> 
> So, that is a NAK from me.
> 

Understood. It occurs to me, though, that it would be trivial to
just add build time assertions to check a few struct member offset
values, and fail out if they changed. That would give us everything:
warnings-free builds, and no silent failures.

Thoughts?

thanks,
-- 
John Hubbard
NVIDIA