Lab1-Part C-2/2: The Kernel (Stack)

[Preface] A Hope That My Crude Remarks May Draw Forth By Abler People

[前言]拋磚引玉


Exercise9:

•  Something needed to know
• Understand how did kernel perform its stack creation. 
• Discussion:
1. Determine where the kernel initializes its stack
• At kern/entry.S
• # Set the stack pointer
• movl    $(bootstacktop),%esp
• f0100034:       bc 00 00 11 f0          mov    $0xf0110000,%esp
2. Where in memory its stack is located
• as above: 0xf0110000
3. How does the kernel reserve space for its stack
• .space KSTKSIZE
• 8*4096 bytes = 8192 stack frames each 4 bytes
4. At which "end" of this reserved area is the stack pointer initialized to point to?
• bootstack
5. push data from bootstacktop to bootstack (each one put is -4)

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Exercise10:

• Something needed to know
• To be familiar with x86 calling convention.
• Each EBP pused into stack
• the base pointer into the stack used by that function: 
• Each EIP pushed into stack
• return instruction. : the instruction address to which control will return when the function returns.
• Set breakpoint at test_backtrace 
1. Examine what happens each time it gets called after the kernel starts
2. How many 32-bit words does each recursive nesting level of test_backtrace push on the stack what are those words?
• EIP/ARGS/EBP
• registers waited to be used
• push its value in, before return, just pop out them.
•  Recursive Calling Stack
• stack as linked list array
• From current EIP
• Old EIPs by finding EBP+4 pushed by gcc calling convention 
• PIC
• Question
• read_eip
• Doesn't work if inlined
• Putting at the end of the file seems to prevent inlining.

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Exercise11:

• Something needed to know
• Based on Exercise10
• Pointer usage
• int*p
• (int)p + 1  -   1base
• (int)(p + 1) - 4base
• GitHub Link
• My Code.

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Exercise12:

• Something needed to know
• Based on Exercise11
• printf(%.*) usage
• Stab format
•  Trace kern/kdebug.c
• GitHub Link:
• My Code.

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Enjoy OS travel :)
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