Middle Ages: The setup( ) Function
by Marco Cesati, Daniel P. Bovet
Understanding the Linux Kernel, Second Edition
- Understanding the Linux Kernel, 2nd Edition
- Preface
- 1. Introduction
- Linux Versus Other Unix-Like Kernels
- Hardware Dependency
- Linux Versions
- Basic Operating System Concepts
- An Overview of the Unix Filesystem
- An Overview of Unix Kernels
- 2. Memory Addressing
- 3. Processes
- 4. Interrupts and Exceptions
- 5. Kernel Synchronization
- Kernel Control Paths
- When Synchronization Is Not Necessary
- Synchronization Primitives
- Synchronizing Accesses to Kernel Data Structures
- Choosing Among Spin Locks, Semaphores, and Interrupt Disabling
- Protecting a data structure accessed by exceptions
- Protecting a data structure accessed by interrupts
- Protecting a data structure accessed by deferrable functions
- Protecting a data structure accessed by exceptions and interrupts
- Protecting a data structure accessed by exceptions and deferrable functions
- Protecting a data structure accessed by interrupts and deferrable functions
- Protecting a data structure accessed by exceptions, interrupts, and deferrable functions
- Choosing Among Spin Locks, Semaphores, and Interrupt Disabling
- Examples of Race Condition Prevention
- 6. Timing Measurements
- 7. Memory Management
- Page Frame Management
- Memory Area Management
- The Slab Allocator
- Cache Descriptor
- Slab Descriptor
- General and Specific Caches
- Interfacing the Slab Allocator with the Buddy System
- Allocating a Slab to a Cache
- Releasing a Slab from a Cache
- Object Descriptor
- Aligning Objects in Memory
- Slab Coloring
- Local Array of Objects in Multiprocessor Systems
- Allocating an Object in a Cache
- Releasing an Object from a Cache
- General Purpose Objects
- Noncontiguous Memory Area Management
- 8. Process Address Space
- The Process’s Address Space
- The Memory Descriptor
- Memory Regions
- Page Fault Exception Handler
- Creating and Deleting a Process Address Space
- Managing the Heap
- 9. System Calls
- 10. Signals
- 11. Process Scheduling
- 12. The Virtual Filesystem
- 13. Managing I/O Devices
- I/O Architecture
- Device Files
- Device Drivers
- Block Device Drivers
- Character Device Drivers
- 14. Disk Caches
- 15. Accessing Files
- 16. Swapping: Methods for Freeing Memory
- What Is Swapping?
- Swap Area
- The Swap Cache
- Transferring Swap Pages
- Swapping Out Pages
- Swapping in Pages
- Reclaiming Page Frame
- 17. The Ext2 and Ext3 Filesystems
- 18. Networking
- 19. Process Communication
- 20. Program Execution
- A. System Startup
- B. Modules
- C. Source Code Structure
- 21. Bibliography
- Index
- Colophon
The code of the setup( ) assembly language
function is placed by the linker immediately after the integrated
boot loader of the kernel—that is, at offset
0x200 of the kernel image file. The boot loader
can therefore easily locate the code and copy it into RAM, starting
from physical address 0x00090200.
The setup( ) function must initialize the hardware
devices in the computer and set up the environment for the execution
of the kernel program. Although the BIOS already initialized most
hardware devices, Linux does not rely on it, but reinitializes the
devices in its own manner to enhance portability and robustness.
setup( ) performs the following operations:
Invokes a BIOS procedure to find out the amount of RAM available in the system.
Sets the keyboard repeat delay and rate. (When the user keeps a key pressed past a certain amount of time, the keyboard device sends the corresponding keycode over and over to the CPU.)
Initializes the video adapter card.
Reinitializes the disk controller and determines the hard disk parameters.
Checks for an IBM Micro Channel bus (MCA).
Checks for a PS/2 pointing device (bus mouse).
Checks for Advanced Power Management (APM) BIOS support.
If the kernel image was loaded low in RAM (at physical address
0x00010000), moves it to physical address0x00001000. Conversely, if the kernel image was loaded high in RAM, the function does not move it. This step is necessary because to be able to store the kernel image on a floppy disk and to save time while booting, the kernel image stored on disk is compressed, and the decompression routine needs some free space to use as a temporary buffer following the kernel image in RAM.Sets up a provisional Interrupt Descriptor Table (IDT) and a provisional Global Descriptor Table (GDT).
Resets the floating-point unit (FPU), if any.
Reprograms the Programmable Interrupt Controller (PIC) and maps the 16 hardware interrupts (IRQ lines) to the range of vectors from 32 to 47. The kernel must perform this step because the BIOS erroneously maps the hardware interrupts in the range from 0 to 15, which is already used for CPU exceptions (see Section 4.2.2).
Switches the CPU from Real Mode to Protected Mode by setting the
PEbit in thecr0status register. The PG bit in thecr0register is cleared, so paging is still disabled.Jumps to the
startup_32( )assembly language function.
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