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