Linux Kernel Architecture

Mauerer app04.tex V1 - 09/04/2008 6:12pm Page 1226

Appendix D: System Startup

management. The bulk of the initialization work — setting up the central data structures of the various

kernel subsystems — is performed instart_kernelonce the command-line arguments passed to

the kernel at startup have been interpreted. This is a very comprehensive task because it involves

practically all subsystems. It is therefore broken down into a large number of short procedures, which

are described in the subsequent sections. The final step is to generate the idle process that the kernel calls

when it has absolutely nothing else to do. Theinitprocess is also started with PID 1 — this runs the

initialization routines of various subsystems and then starts/sbin/initas the first user space process.

This concludes kernel-side initialization.

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Architecture-specfic, high-level setup for memory management

Evaluate command-line arguments

Initialize core data structures of most subsystems

Determine processor and system errors

Start idle process and init thread

start_kernel

Figure D-1: Code flow diagram forstart_kernel.

Architecture-SpecificSetup

As its name clearly suggests,setup_archis an architecture-specific function. It performs setup tasks writ-

ten in C and concerns itself primarily with the initialization of various aspects of memory management.

For example, on most systems, it finalizes enabling of paging and sets up suitable data structures for ker-

nel mode. On some architectures with several variants (IA-64 and Alpha, for example), variant-specific

setup is performed at this point.

For simplicity’s sake, this section examines only the implementation ofsetup_archfor IA-32 systems as

toucheduponbrieflyinChapter3.FigureD-2shows the corresponding code flow diagram.

Determine position of kernel in memory

setup_arch

parse_early_param

setup_memory

paging_init

Figure D-2: Code flow diagram

forsetup_archon IA-32 systems.