Implement system image loader

[jserv]

After Issue #11 is done, it means F9 Microkernel could have a separate userspace environment, which might be initialized by certain system loader. Upon the ideas of @georgekang, here are the expected features of system loader:

• F9 microkernel itself should be minimized, and the 1st stage image only includes low level parts + system loader
• system loader locates the address which points the image of userspace environment
• system loader, included in 1st stage image, attempts to load F9 Microkernel to memory (RamLoc, 0x20000000) and then userspace environment to other area according to its descriptor.
• loader switches the mapping configuration and jump to __l4_start, which is the entry of F9 Microkernel.
• all userspace environment is initialized by F9 microkernel.

[georgekang]

WIP: https://github.com/georgekang/f9-kernel/commits/loader
Here are the build instructions:

• Build f9 without KProbes
• cd loader
• make; make flash

[jserv]

The reference boot messages:

loading kernel ...
elf check result = 0
Number of program headers: 1
Elf file pheader physical: 0x20000000
Elf file
====================================================
      Copyright(C) 2013 The F9 Microkernel Project  
====================================================
Git head: 17069e043b9c3a0d02712382ae447772093dd728
Host: x86_64
Build: 2013-09-20T21:39:37+0800

[georgekang]

WIP(V2): e3d5809
Support breakpoint in kernel.

[BohuTANG]

How to run F9 in qemu?
Thanks.

[jserv]

@shuttler Currently, QEMU doesn't support enough features that F9 Microkernel requires, such as MPU.
Therefore, F9 can only run on STM32F4-Discovery board.

[georgekang]

Now loader can load kernel and l4 user space to sram and run them.
Please reference it. https://github.com/georgekang/f9-kernel/tree/loader/loader
However, there are some hard works to merge build system and some duplicated codes.

[jserv]

Per the discussion between @georgekang and me, WIP is expected to accomplish the following:

• clarify the branch name to elf-loader
• adapt the unified common parts for linker scripts
• revise build system to avoid the duplicated
• Kconfig entries

[jserv]

Take! I'm working on splitting the changes into smaller and dedicated ones.

[jserv]

It is supposedly done.