linux-kernel - Re: [PATCH v7u1 22/31] x86, boot: add fields to support load bzImage and ramdisk above 4G

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Date:	Mon, 14 Jan 2013 15:10:25 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>, Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kiszka <jan.kiszka@....de>,
	Jason Wessel <jason.wessel@...driver.com>,
	linux-kernel@...r.kernel.org, Rob Landley <rob@...dley.net>,
	Matt Fleming <matt.fleming@...el.com>,
	Gokul Caushik <caushik1@...il.com>,
	Josh Triplett <josh@...htriplett.org>,
	Joe Millenbach <jmillenbach@...il.com>
Subject: Re: [PATCH v7u1 22/31] x86, boot: add fields to support load bzImage
 and ramdisk above 4G

On 01/13/2013 01:41 PM, Borislav Petkov wrote:
>> diff --git a/arch/x86/boot/compressed/cmdline.c b/arch/x86/boot/compressed/cmdline.c
>> index b4c913c..bffd73b 100644
>> --- a/arch/x86/boot/compressed/cmdline.c
>> +++ b/arch/x86/boot/compressed/cmdline.c
>> @@ -17,6 +17,8 @@ static unsigned long get_cmd_line_ptr(void)
>>  {
>>  	unsigned long cmd_line_ptr = real_mode->hdr.cmd_line_ptr;
>>  
>> +	cmd_line_ptr |= (u64)real_mode->ext_cmd_line_ptr << 32;
>> +
>>  	return cmd_line_ptr;
>>  }
> 
> On 32-bit, this unsigned long cmd_line_ptr is 4 bytes and the OR doesn't
> have any effect on the final result. You probably want to do:
> 
> #ifdef CONFIG_64BIT
> 	cmd_line_ptr |= (u64)real_mode->ext_cmd_line_ptr << 32;
> #endif
> 
> right?
> 

Actually, on 32 bits the compiler will simply drop the statement on the
floor, no #ifdef required.  If gcc outputs a warning we should do
something about it, otherwise we can just plain ignore it.

	-hpa


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