Linux Kernel Architecture

Mauerer runapp01.tex V1 - 09/04/2008 6:08pm Page 1130

Appendix A: Architecture Specifics

system calls. The C or assembler code of the kernel need not save all registers listed inpt_regsbecause

some of them are automatically placed on the stack by PAL code routines. Those that need be are the

following:

include/asm-alpha/ptrace.h

struct pt_regs {

unsigned long r0;

unsigned long r1;

unsigned long r2;

unsigned long r3;

unsigned long r4;

unsigned long r5;

unsigned long r6;

unsigned long r7;

unsigned long r8;

unsigned long r19;

unsigned long r20;

unsigned long r21;

unsigned long r22;

unsigned long r23;

unsigned long r24;

unsigned long r25;

unsigned long r26;

unsigned long r27;

unsigned long r28;

unsigned long hae;

/* JRP - These are the values provided to a0-a2 by PALcode */

unsigned long trap_a0;

unsigned long trap_a1;

unsigned long trap_a2;

/* These are saved by PAL-code: */

unsigned long ps;

unsigned long pc;

unsigned long gp;

unsigned long r16;

unsigned long r17;

unsigned long r18;

};

This architecture likewise makes use of an emptythread_structstructure:

include/asm-alpha/processor.h

/* This is dead. Everything has been moved to thread_info. */

struct thread_struct { };

The contents of floating-point registersf0tof31are not held inthread_info, but instead are held on

the stack using the following structure (a few integer registers are saved as well as the floating-point

registers; normally, the former are not needed by the kernel):

include/asm-alpha/ptrace.h

struct switch_stack {

unsigned long r9;

unsigned long r10;

unsigned long r11;