linux/arch/x86/include/asm/debugreg.h

#ifndef _ASM_X86_DEBUGREG_H
#define _ASM_X86_DEBUGREG_H


/* Indicate the register numbers for a number of the specific
   debug registers.  Registers 0-3 contain the addresses we wish to trap on */
#define DR_FIRSTADDR 0        /* u_debugreg[DR_FIRSTADDR] */
#define DR_LASTADDR 3         /* u_debugreg[DR_LASTADDR]  */

#define DR_STATUS 6           /* u_debugreg[DR_STATUS]     */
#define DR_CONTROL 7          /* u_debugreg[DR_CONTROL] */

/* Define a few things for the status register.  We can use this to determine
   which debugging register was responsible for the trap.  The other bits
   are either reserved or not of interest to us. */

/* Define reserved bits in DR6 which are always set to 1 */
#define DR6_RESERVED	(0xFFFF0FF0)

#define DR_TRAP0	(0x1)		/* db0 */
#define DR_TRAP1	(0x2)		/* db1 */
#define DR_TRAP2	(0x4)		/* db2 */
#define DR_TRAP3	(0x8)		/* db3 */
#define DR_TRAP_BITS	(DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)

#define DR_STEP		(0x4000)	/* single-step */
#define DR_SWITCH	(0x8000)	/* task switch */

/* Now define a bunch of things for manipulating the control register.
   The top two bytes of the control register consist of 4 fields of 4
   bits - each field corresponds to one of the four debug registers,
   and indicates what types of access we trap on, and how large the data
   field is that we are looking at */

#define DR_CONTROL_SHIFT 16 /* Skip this many bits in ctl register */
#define DR_CONTROL_SIZE 4   /* 4 control bits per register */

#define DR_RW_EXECUTE (0x0)   /* Settings for the access types to trap on */
#define DR_RW_WRITE (0x1)
#define DR_RW_READ (0x3)

#define DR_LEN_1 (0x0) /* Settings for data length to trap on */
#define DR_LEN_2 (0x4)
#define DR_LEN_4 (0xC)
#define DR_LEN_8 (0x8)

/* The low byte to the control register determine which registers are
   enabled.  There are 4 fields of two bits.  One bit is "local", meaning
   that the processor will reset the bit after a task switch and the other
   is global meaning that we have to explicitly reset the bit.  With linux,
   you can use either one, since we explicitly zero the register when we enter
   kernel mode. */

#define DR_LOCAL_ENABLE_SHIFT 0    /* Extra shift to the local enable bit */
#define DR_GLOBAL_ENABLE_SHIFT 1   /* Extra shift to the global enable bit */
#define DR_LOCAL_ENABLE (0x1)      /* Local enable for reg 0 */
#define DR_GLOBAL_ENABLE (0x2)     /* Global enable for reg 0 */
#define DR_ENABLE_SIZE 2           /* 2 enable bits per register */

#define DR_LOCAL_ENABLE_MASK (0x55)  /* Set  local bits for all 4 regs */
#define DR_GLOBAL_ENABLE_MASK (0xAA) /* Set global bits for all 4 regs */

/* The second byte to the control register has a few special things.
   We can slow the instruction pipeline for instructions coming via the
   gdt or the ldt if we want to.  I am not sure why this is an advantage */

#ifdef __i386__
#define DR_CONTROL_RESERVED (0xFC00) /* Reserved by Intel */
#else
#define DR_CONTROL_RESERVED (0xFFFFFFFF0000FC00UL) /* Reserved */
#endif

#define DR_LOCAL_SLOWDOWN (0x100)   /* Local slow the pipeline */
#define DR_GLOBAL_SLOWDOWN (0x200)  /* Global slow the pipeline */

/*
 * HW breakpoint additions
 */
#ifdef __KERNEL__

DECLARE_PER_CPU(unsigned long, cpu_dr7);

static inline void hw_breakpoint_disable(void)
{
	/* Zero the control register for HW Breakpoint */
	set_debugreg(0UL, 7);

	/* Zero-out the individual HW breakpoint address registers */
	set_debugreg(0UL, 0);
	set_debugreg(0UL, 1);
	set_debugreg(0UL, 2);
	set_debugreg(0UL, 3);
}

static inline int hw_breakpoint_active(void)
{
	return __this_cpu_read(cpu_dr7) & DR_GLOBAL_ENABLE_MASK;
}

extern void aout_dump_debugregs(struct user *dump);

extern void hw_breakpoint_restore(void);

#endif	/* __KERNEL__ */

#endif /* _ASM_X86_DEBUGREG_H */