User/Kernel modes in ARM for micro-C Linux

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Hi all
The basic requirement for a hardware to support Linux is existance of
user/kernel modes in hardware , is that true for MMU-less Linux-s like
mu-C Linux as well?
If that is true how is a MMU-less Linux supported on a simple ARM core
(e,g ARM7) where to the best of my knowledge privileged address-space
cannot be demarcated , atleast not in hardware - or is there a
software abstraction in Linux which does this.
Please help.

K V

Re: User/Kernel modes in ARM for micro-C Linux
Hi KV,


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Not at all.  We ported uClinux to the Xilinx microblaze FPGA-based
processor, which has absolutely no concept of user or kernel mode.

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The kernel and user space share the same linear address space.  When a
user application is loaded, the kernel allocates space for its code,
data and stack segments (stack is a fixed size at runtime, this is one
side-effect of no MMU), then the binary is relocated up to the correct
address.

John

Re: User/Kernel modes in ARM for micro-C Linux

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I should clarify, that's not entirely true.  There is a bit in the
Microblaze processor status register that could theoretically be used as
a kind of kernel/user mode flag, but it has nothing to do with memory or
address spaces.

John

Re: User/Kernel modes in ARM for micro-C Linux
snipped-for-privacy@hotmail.com (k v) wrote in message
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i think it has no memory protection. any application can write to any
part of memory but some cpus allow certain memory regions to be
protected

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