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built-in command line vs. bootloader-supplied

To: "linux-mips@linux-mips.org" <linux-mips@linux-mips.org>
Subject: built-in command line vs. bootloader-supplied
From: Ricard Wanderlof <ricard.wanderlof@axis.com>
Date: Tue, 8 Nov 2011 16:23:14 +0100 (CET)
Sender: linux-mips-bounce@linux-mips.org

Hi,

This is my first post to the list, not having had the need to delve into the MIPS port at this level before.

When the CONFIG_CMDLINE_BOOL is set, a built-in command line can be set in CONFIG_CMDLINE by virtue of arch/mips/kernel/setup.c:arch_mem_init() .

If the boot loader supplies an additional command line (picked up by various sub-architecture-specific routines (to pick an example, pmc-sierra/msp71xx/msp_prom.c:prom_init_cmdline())), it can be concatenated with the built-in command line. This is not supported for all architectures, but it is for x86 and MIPS. However, one difference is that for x86, the bootloader-supplied command line is appended to the kernel built-in one, but for MIPS it's the other way around: the bootloader-supplied commands end up first in the command line string, appended by the built-in command line.

Is there any reason that it is like this? I could guess a number of reasons for one or the other, but it would be nice if someone has a more definitive answer. Or is it actually a bug? It would seem that it should at least be consistent across architectures.

Looking at the git log, the current state of affairs was committed 2009-09-21 by Dmitri Vorobiev, stating in the commit message " ... in a manner identical to what is currently used for x86." . But at the time x86 worked as today, i.e. with the builtin first, appended by the bootloader-supplied one.

Thanks for any pointers.

/Ricard
--
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30

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