Linux Kernel Architecture

Mauerer runapp01.tex V1 - 09/04/2008 6:08pm Page 1127

Appendix A: Architecture Specifics

The symbolic names of the registers and their positions within the array are defined by means of pre-
processor constants:

include/asm-arm/ptrace.h

#define ARM_cpsr uregs[16]

#define ARM_pc uregs[15]

#define ARM_lr uregs[14]

#define ARM_sp uregs[13]

#define ARM_ip uregs[12]

#define ARM_fp uregs[11]

#define ARM_r10 uregs[10]

#define ARM_r9 uregs[9]

#define ARM_r8 uregs[8]

#define ARM_r7 uregs[7]

#define ARM_r6 uregs[6]

#define ARM_r5 uregs[5]

#define ARM_r4 uregs[4]

#define ARM_r3 uregs[3]

#define ARM_r2 uregs[2]

#define ARM_r1 uregs[1]

#define ARM_r0 uregs[0]

#define ARM_ORIG_r0 uregs[17]

It is not necessary to save any floating-point registers because ARM processors provide only software
support for floating-point operations:

include/asm-arm/processor.h

struct thread_struct {

/* fault info */

unsigned long address;

unsigned long trap_no;

unsigned long error_code;

/* debugging */

struct debug_info debug;

};

However, machine instructions (in the form of their opcode) can be saved together with a memory
address for debugging purposes, as shown here:

include/asm-arm/processor.h

union debug_insn {

u32 arm;

u16 thumb;

};

struct debug_entry {

u32 address;

union debug_insn insn;

};

struct debug_info {

int nsaved;

struct debug_entry bp[2];

};