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3.5. SWEB BOOT PROCESS CHAPTER 3. VM, PROTECTION AND PAGING Index Base Limit P DPL S Type A G D X U [24] [20] [1] [2] [1] [3] [1] [1] [1] [1] [1] 0 0 0 0 00 0 000 0 0 0 0 0 1 0 0 0 00 0 000 0 0 0 0 0 2 0 FFFFFh 1 00 1 001 0 1 1 0 0 3 0 FFFFFh 1 00 1 101 0 1 1 0 0 4 0 FFFFFh 1 11 1 001 0 1 1 0 0 5 0 FFFFFh 1 11 1 101 0 1 1 0 0 Table 3.7: Sweb Global segment Descriptor Table 3. zero out kernel BSS (uninitialized data section) 4. set up stack (which is in the BSS section) 5. call parseMultibootHeader() 6. call initialiseBootTimePaging() 7. enable PSE (extended PageSize 4k and 4m mixed) 8. enable Paging (PG bit = 1) 9. Paging Mode: 10. reload GDT with new address 11. load LINEAR_DATA_SEL into all segment registers 12. call removeBootTimeIdentMapping() 13. reload CR3 14. call startup() 14. 1. init KernelMemoryManager 14. 2. init PageManager 14. 3. init Console 14. 4. init Scheduler 14. 5. init kprintf_no_sleep 14. 6. init KernelThreadInfo 14. 7. init Interrupts 14. 8. add Threads 14. 9. enable synchronisation mechanisms in KMM and PM 14. 10. enable Interrupts: from here on, tasks are executed pseudo-parallel. 14. 11. yield away for details, refer to the files init_boottime_pagetables.cpp, boot.s and main.cpp. 3.5.2 Sweb Global Descriptor Sweb’s boot time GDT can be found in boot.s and Table 3.7 with a per-descriptor elaboration in Table 3.8. 44 of 151
CHAPTER 3. VM, PROTECTION AND PAGING 3.5. SWEB BOOT PROCESS Index Base Limit Priv.Lvl. Type Symbol 2 0 4GiB 0 Data, read/write LINEAR_DATA_SEL 3 0 4GiB 0 Code, execute/read LINEAR_CODE_SEL 4 0 4GiB 3 Data, read/write LINEAR_USR_DATA_SEL 5 0 4GiB 3 Code, execute/read LINEAR_USR_CODE_SEL Table 3.8: Sweb GDT, more readable 3.5.3 Sweb Boot-Time Paging As long as paging is disabled during the boot-phase, we are accessing physical memory directly. This makes it easy to get information about the location of grub loaded modules or access memory used by hardware. The problem in this phase stems from the fact that all kernel pointers are compiled with a 2GiB offset, since the kernel is meant to be accessed at 2GiB in linear memory. Physically though, the kernel starts executing at 1MiB. In order to run the Kernel at 2GiB, an initial Page-Directory is set up so that kernelcode is accessible through both its physical location as well as above 2GiB. After the end of the linear kernel location, mappings to free physical pages are added, which we can use as kernel memory.. With this mapping in place, paging is enabled and the first call to above 2GiB is made. Actually, directly calling a kernel function prior to enabled paging is impossible. We would jump 2GiB far away from our code. Therefore, during boot-time, an offset is substracted from the function-addresses before calling them. The call to void initialiseBootTimePaging() which lacks this measure, works because gcc optimises the function call by inlining the code. 3.5.4 Sweb Post-Boot Paging Setup After the boot phase has finished, the linear memory of Sweb is partitioned like shown in Table 3.9. Because of page protection, the kernel can directly access user space code while access to kernel code is denied to the user program even though kernel and user program share the same linear address space. More exactly, every user program’s Page-Directory also contains the mapping of the kernel pages. The identity mapping (with a 3GiB offset) beyond 3GiB is used to communicate with hardware like the frame buffer.
Page 1 and 2: The holy bible of SWEB SWEB-Crew Se
Page 3 and 4: Contents 1 Install 13 1.1 some note
Page 5 and 6: CONTENTS CONTENTS 6 System Calls 71
Page 7 and 8: CONTENTS CONTENTS 11.6.9Running Xen
Page 9 and 10: List of Figures 3.1 Protected Mode
Page 11 and 12: List of Tables 3.1 Segment Descript
Page 13 and 14: Chapter 1 Install Basic guidelines
Page 15 and 16: CHAPTER 1. INSTALL 1.2. RUNNING SWE
Page 17 and 18: CHAPTER 1. INSTALL 1.3. DEVELOPERS
Page 19 and 20: Chapter 2 GDB 2.1 General The GNU P
Page 21 and 22: CHAPTER 2. GDB 2.5. USING DDD The d
Page 23 and 24: CHAPTER 2. GDB 2.5. USING DDD To ge
Page 25 and 26: Chapter 3 VM, Protection and Paging
Page 27 and 28: CHAPTER 3. VM, PROTECTION AND PAGIN
Page 43: CHAPTER 3. VM, PROTECTION AND PAGIN
Page 55 and 56: Chapter 4 Kernelspace Memory Manage
Page 57 and 58: CHAPTER 4. KERNELSPACE MEMORY MANAG
Page 59 and 60: CHAPTER 4. KERNELSPACE MEMORY MANAG
Page 61 and 62: Chapter 5 Threads and Processes 5.1
Page 63 and 64: CHAPTER 5. THREADS AND PROCESSES 5.
Page 65 and 66: CHAPTER 5. THREADS AND PROCESSES5.4
Page 71 and 72: Chapter 6 System Calls 6.1 Base Inf
Page 73 and 74: CHAPTER 6. SYSTEM 6.2. CALLS SYSTEM
Page 75 and 76: CHAPTER 6. SYSTEM CALLS 6.3. SYSTEM
Page 81 and 82: Chapter 7 Character Devices 7.1 Int
Page 83 and 84: CHAPTER 7. CHARACTER DEVICES 7.3. C
Page 85 and 86: CHAPTER 7. CHARACTER DEVICES 7.4. K
Page 87 and 88: CHAPTER 7.5. SERIAL 7. CHARACTER PO
Page 93 and 94: CHAPTER 7. CHARACTER DEVICES 7.7. T
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CHAPTER 7. CHARACTER DEVICES 7.7. T
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CHAPTER 7. CHARACTER DEVICES 7.8. C
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Chapter 8 Block Devices 8.1 Introdu
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CHAPTER 8. BLOCK DEVICES 8.2. IMPLE
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Chapter 9 VFS, FS 9.1 Introduction
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CHAPTER 9. VFS, FS 9.3. VFS DATA ST
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CHAPTER 9. VFS, FS 9.4. RAMFS - MEM
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Chapter 10 Locking 10.1 Introductio
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CHAPTER 10. LOCKING 10.2. LOCKS 10.
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CHAPTER 10. LOCKING 10.4. CRITICAL
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Chapter 11 Xen 11.1 Introduction Th
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CHAPTER 11. XEN 11.3. XEN Xen diffe
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CHAPTER 11. XEN 11.4. SWEB- XEN 11.
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CHAPTER 11. XEN 11.4. SWEB- XEN 21
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CHAPTER 11. XEN 11.4. SWEB- XEN Fig
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CHAPTER 11. XEN 11.4. SWEB- XEN 11.
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CHAPTER 11. XEN 11.4. SWEB- XEN Fig
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CHAPTER 11. XEN 11.6. APPENDIX: INS
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Chapter 12 Hacking Sweb This chapte
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Bibliography [1] Wikipedia:Binary_p
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