Re: kgdb-lite for 2.6.2 (i386 specific parts)

["Amit S. Kale" <amitkale@emsyssoft.com>]

On Tuesday 17 Feb 2004 5:10 pm, Pavel Machek wrote:
> Hi!
>
> These are i386-specific parts. They probably can't go in as-is.
>
> Change that worries me most is change of do_IRQ calling convention. If
> that is dropped, kgdb will still work, but traceback through interrupt
> will be impossible; right?

Yes. do_IRQ calling convention required only for backtrace to go through an 
interrupt entry point. 

-Amit


> 								Pavel
>
> --- clean.2.5/arch/i386/Kconfig	2004-02-05 01:53:54.000000000 +0100
> +++ linux-mm/arch/i386/Kconfig	2004-02-16 23:15:53.000000000 +0100
> @@ -1253,6 +1253,20 @@
>  	  If you say Y here, various routines which may sleep will become very
>  	  noisy if they are called with a spinlock held.
>
> +config KGDB
> +	bool "KGDB: kernel debugging with remote gdb"
> +	depends on DEBUG_KERNEL
> +	select DEBUG_INFO
> +	select FRAME_POINTER
> +	help
> +	  If you say Y here, it will be possible to remotely debug the
> +	  kernel using gdb. This enlarges your kernel image disk size by
> +	  several megabytes and requires a machine with more than 128 MB
> +	  RAM to avoid excessive linking time.
> +	  Documentation of kernel debugger available at
> +	  http://kgdb.sourceforge.net
> +	  This is only useful for kernel hackers. If unsure, say N.
> +
>  config FRAME_POINTER
>  	bool "Compile the kernel with frame pointers"
>  	help
> --- clean.2.5/arch/i386/kernel/Makefile	2004-01-09 20:24:13.000000000 +0100
> +++ linux-mm/arch/i386/kernel/Makefile	2004-02-16 23:09:06.000000000 +0100
> @@ -31,6 +31,7 @@
>  obj-$(CONFIG_ACPI_SRAT) 	+= srat.o
>  obj-$(CONFIG_HPET_TIMER) 	+= time_hpet.o
>  obj-$(CONFIG_EFI) 		+= efi.o efi_stub.o
> +obj-$(CONFIG_KGDB)		+= i386-stub.o
>
>  EXTRA_AFLAGS   := -traditional
>
> --- clean.2.5/arch/i386/kernel/entry.S	2003-11-24 17:08:26.000000000 +0100
> +++ linux-mm/arch/i386/kernel/entry.S	2004-02-16 23:09:06.000000000 +0100
> @@ -399,7 +399,17 @@
>  	ALIGN
>  common_interrupt:
>  	SAVE_ALL
> +	movl %esp, %eax
> +/* Create a fake function call followed by a fake function prologue to
> fool + * gdb into believing that this is a normal function call. */
> +	pushl EIP(%eax)
> +
> +common_interrupt_1:
> +	pushl %ebp
> +	movl %esp, %ebp
> +	pushl %eax
>  	call do_IRQ
> +	addl $12, %esp
>  	jmp ret_from_intr
>
>  #define BUILD_INTERRUPT(name, nr)	\
> --- clean.2.5/arch/i386/kernel/i386-stub.c	2004-02-17 11:39:06.000000000
> +0100 +++ linux-mm/arch/i386/kernel/i386-stub.c	2004-02-16
> 23:09:06.000000000 +0100 @@ -0,0 +1,373 @@
> +/*
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License as published by the
> + * Free Software Foundation; either version 2, or (at your option) any
> + * later version.
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + *
> + */
> +
> +/*
> + * Copyright (C) 2000-2001 VERITAS Software Corporation.
> + */
> +/*
> + *  Contributor:     Lake Stevens Instrument Division$
> + *  Written by:      Glenn Engel $
> + *  Updated by:	     Amit Kale<akale@veritas.com>
> + *  Modified for 386 by Jim Kingdon, Cygnus Support.
> + *  Origianl kgdb, compatibility with 2.1.xx kernel by David Grothe
> <dave@gcom.com> + */
> +
> +#include <linux/string.h>
> +#include <linux/kernel.h>
> +#include <linux/sched.h>
> +#include <linux/smp.h>
> +#include <linux/spinlock.h>
> +#include <linux/delay.h>
> +#include <asm/vm86.h>
> +#include <asm/system.h>
> +#include <asm/ptrace.h>			/* for linux pt_regs struct */
> +#include <linux/kgdb.h>
> +#ifdef CONFIG_GDB_CONSOLE
> +#include <linux/console.h>
> +#endif
> +#include <linux/init.h>
> +#include <linux/debugger.h>
> +
> +/* Put the error code here just in case the user cares.  */
> +int gdb_i386errcode;
> +/* Likewise, the vector number here (since GDB only gets the signal
> +   number through the usual means, and that's not very specific).  */
> +int gdb_i386vector = -1;
> +
> +#if KGDB_MAX_NO_CPUS != 8
> +#error change the definition of slavecpulocks
> +#endif
> +
> +void regs_to_gdb_regs(unsigned long *gdb_regs, struct pt_regs *regs)
> +{
> +    gdb_regs[_EAX] =  regs->eax;
> +    gdb_regs[_EBX] =  regs->ebx;
> +    gdb_regs[_ECX] =  regs->ecx;
> +    gdb_regs[_EDX] =  regs->edx;
> +    gdb_regs[_ESI] =  regs->esi;
> +    gdb_regs[_EDI] =  regs->edi;
> +    gdb_regs[_EBP] =  regs->ebp;
> +    gdb_regs[ _DS] =  regs->xds;
> +    gdb_regs[ _ES] =  regs->xes;
> +    gdb_regs[ _PS] =  regs->eflags;
> +    gdb_regs[ _CS] =  regs->xcs;
> +    gdb_regs[ _PC] =  regs->eip;
> +    gdb_regs[_ESP] =  (int) (&regs->esp) ;
> +    gdb_regs[ _SS] =  __KERNEL_DS;
> +    gdb_regs[ _FS] =  0xFFFF;
> +    gdb_regs[ _GS] =  0xFFFF;
> +}
> +
> +void sleeping_thread_to_gdb_regs(unsigned long *gdb_regs, struct
> task_struct *p) +{
> +	gdb_regs[_EAX] = 0;
> +	gdb_regs[_EBX] = 0;
> +	gdb_regs[_ECX] = 0;
> +	gdb_regs[_EDX] = 0;
> +	gdb_regs[_ESI] = 0;
> +	gdb_regs[_EDI] = 0;
> +	gdb_regs[_EBP] = *(int *)p->thread.esp;
> +	gdb_regs[_DS]  = __KERNEL_DS;
> +	gdb_regs[_ES]  = __KERNEL_DS;
> +	gdb_regs[_PS]  = 0;
> +	gdb_regs[_CS]  = __KERNEL_CS;
> +	gdb_regs[_PC]  = p->thread.eip;
> +	gdb_regs[_ESP] = p->thread.esp;
> +	gdb_regs[_SS]  = __KERNEL_DS;
> +	gdb_regs[_FS]  = 0xFFFF;
> +	gdb_regs[_GS]  = 0xFFFF;
> +}
> +
> +void gdb_regs_to_regs(unsigned long *gdb_regs, struct pt_regs *regs)
> +{
> +    regs->eax	=     gdb_regs[_EAX] ;
> +    regs->ebx	=     gdb_regs[_EBX] ;
> +    regs->ecx	=     gdb_regs[_ECX] ;
> +    regs->edx	=     gdb_regs[_EDX] ;
> +    regs->esi	=     gdb_regs[_ESI] ;
> +    regs->edi	=     gdb_regs[_EDI] ;
> +    regs->ebp	=     gdb_regs[_EBP] ;
> +    regs->xds	=     gdb_regs[ _DS] ;
> +    regs->xes	=     gdb_regs[ _ES] ;
> +    regs->eflags=     gdb_regs[ _PS] ;
> +    regs->xcs	=     gdb_regs[ _CS] ;
> +    regs->eip	=     gdb_regs[ _PC] ;
> +#if 0					/* can't change these */
> +    regs->esp	=     gdb_regs[_ESP] ;
> +    regs->xss	=     gdb_regs[ _SS] ;
> +    regs->fs	=     gdb_regs[ _FS] ;
> +    regs->gs	=     gdb_regs[ _GS] ;
> +#endif
> +
> +}
> +
> +struct hw_breakpoint {
> +	unsigned enabled;
> +	unsigned type;
> +	unsigned len;
> +	unsigned addr;
> +} breakinfo[4] = { {
> +enabled:0}, {
> +enabled:0}, {
> +enabled:0}, {
> +enabled:0}};
> +
> +void kgdb_correct_hw_break(void)
> +{
> +	int breakno;
> +	int correctit;
> +	int breakbit;
> +	unsigned dr7;
> +
> +	asm volatile ("movl %%db7, %0\n":"=r" (dr7)
> +		      :);
> +	do {
> +		unsigned addr0, addr1, addr2, addr3;
> +		asm volatile ("movl %%db0, %0\n"
> +			      "movl %%db1, %1\n"
> +			      "movl %%db2, %2\n"
> +			      "movl %%db3, %3\n":"=r" (addr0), "=r"(addr1),
> +			      "=r"(addr2), "=r"(addr3):);
> +	} while (0);
> +	correctit = 0;
> +	for (breakno = 0; breakno < 3; breakno++) {
> +		breakbit = 2 << (breakno << 1);
> +		if (!(dr7 & breakbit) && breakinfo[breakno].enabled) {
> +			correctit = 1;
> +			dr7 |= breakbit;
> +			dr7 &= ~(0xf0000 << (breakno << 2));
> +			dr7 |= (((breakinfo[breakno].len << 2) |
> +				 breakinfo[breakno].type) << 16) <<
> +			    (breakno << 2);
> +			switch (breakno) {
> +			case 0:
> +				asm volatile ("movl %0, %%dr0\n"::"r"
> +					      (breakinfo[breakno].addr));
> +				break;
> +
> +			case 1:
> +				asm volatile ("movl %0, %%dr1\n"::"r"
> +					      (breakinfo[breakno].addr));
> +				break;
> +
> +			case 2:
> +				asm volatile ("movl %0, %%dr2\n"::"r"
> +					      (breakinfo[breakno].addr));
> +				break;
> +
> +			case 3:
> +				asm volatile ("movl %0, %%dr3\n"::"r"
> +					      (breakinfo[breakno].addr));
> +				break;
> +			}
> +		} else if ((dr7 & breakbit) && !breakinfo[breakno].enabled) {
> +			correctit = 1;
> +			dr7 &= ~breakbit;
> +			dr7 &= ~(0xf0000 << (breakno << 2));
> +		}
> +	}
> +	if (correctit) {
> +		asm volatile ("movl %0, %%db7\n"::"r" (dr7));
> +	}
> +}
> +
> +int kgdb_remove_hw_break(unsigned long addr, int type)
> +{
> +	int i, idx = -1;
> +	for (i = 0; i < 4; i ++) {
> +		if (breakinfo[i].addr == addr && breakinfo[i].enabled) {
> +			idx = i;
> +			break;
> +		}
> +	}
> +	if (idx == -1)
> +		return -1;
> +
> +	breakinfo[idx].enabled = 0;
> +	return 0;
> +}
> +
> +int kgdb_set_hw_break(unsigned long addr, int type)
> +{
> +	int i, idx = -1;
> +	for (i = 0; i < 4; i ++) {
> +		if (!breakinfo[i].enabled) {
> +			idx = i;
> +			break;
> +		}
> +	}
> +	if (idx == -1)
> +		return -1;
> +
> +	breakinfo[idx].enabled = 1;
> +	breakinfo[idx].type = type;
> +	breakinfo[idx].len = 1;
> +	breakinfo[idx].addr = addr;
> +	return 0;
> +}
> +
> +int remove_hw_break(unsigned breakno)
> +{
> +	if (!breakinfo[breakno].enabled) {
> +		return -1;
> +	}
> +	breakinfo[breakno].enabled = 0;
> +	return 0;
> +}
> +
> +int set_hw_break(unsigned breakno,
> +		 unsigned type, unsigned len, unsigned addr)
> +{
> +	if (breakinfo[breakno].enabled) {
> +		return -1;
> +	}
> +	breakinfo[breakno].enabled = 1;
> +	breakinfo[breakno].type = type;
> +	breakinfo[breakno].len = len;
> +	breakinfo[breakno].addr = addr;
> +	return 0;
> +}
> +
> +void kgdb_printexceptioninfo(int exceptionNo, int errorcode, char *buffer)
> +{
> +	unsigned	dr6;
> +	int		i;
> +	switch (exceptionNo) {
> +	case 1:		/* debug exception */
> +		break;
> +	case 3:		/* breakpoint */
> +		sprintf(buffer, "Software breakpoint");
> +		return;
> +	default:
> +		sprintf(buffer, "Details not available");
> +		return;
> +	}
> +	asm volatile ("movl %%db6, %0\n":"=r" (dr6)
> +		      :);
> +	if (dr6 & 0x4000) {
> +		sprintf(buffer, "Single step");
> +		return;
> +	}
> +	for (i = 0; i < 4; ++i) {
> +		if (dr6 & (1 << i)) {
> +			sprintf(buffer, "Hardware breakpoint %d", i);
> +			return;
> +		}
> +	}
> +	sprintf(buffer, "Unknown trap");
> +	return;
> +}
> +
> +void kgdb_disable_hw_debug(struct pt_regs *regs)
> +{
> +	/* Disable hardware debugging while we are in kgdb */
> +	asm volatile("movl %0,%%db7": /* no output */ : "r"(0));
> +}
> +
> +void kgdb_post_master_code(struct pt_regs *regs, int eVector, int
> err_code) +{
> +	/* Master processor is completely in the debugger */
> +	gdb_i386vector = eVector;
> +	gdb_i386errcode = err_code;
> +}
> +
> +int kgdb_arch_handle_exception(int exceptionVector, int signo,
> +		int err_code, char *remcomInBuffer, char *remcomOutBuffer,
> +		struct pt_regs *linux_regs)
> +{
> +	long addr, length;
> +	long breakno, breaktype;
> +	char *ptr;
> +	int newPC;
> +	int dr6;
> +
> +	switch (remcomInBuffer[0]) {
> +	case 'c':
> +	case 's':
> +		if (kgdb_contthread && kgdb_contthread != current) {
> +			strcpy(remcomOutBuffer, "E00");
> +			break;
> +		}
> +
> +		kgdb_contthread = NULL;
> +
> +		/* try to read optional parameter, pc unchanged if no parm */
> +		ptr = &remcomInBuffer[1];
> +		if (kgdb_hex2long(&ptr, &addr)) {
> +			linux_regs->eip = addr;
> +		}
> +		newPC = linux_regs->eip;
> +
> +		/* clear the trace bit */
> +		linux_regs->eflags &= 0xfffffeff;
> +
> +		/* set the trace bit if we're stepping */
> +		if (remcomInBuffer[0] == 's') {
> +			linux_regs->eflags |= 0x100;
> +			debugger_step = 1;
> +		}
> +
> +		asm volatile ("movl %%db6, %0\n" : "=r" (dr6));
> +		if (!(dr6 & 0x4000)) {
> +			for (breakno = 0; breakno < 4; ++breakno) {
> +				if (dr6 & (1 << breakno)) {
> +					if (breakinfo[breakno].type == 0) {
> +						/* Set restore flag */
> +						linux_regs->eflags |= 0x10000;
> +						break;
> +					}
> +				}
> +			}
> +		}
> +		kgdb_correct_hw_break();
> +		asm volatile ("movl %0, %%db6\n"::"r" (0));
> +
> +		return (0);
> +
> +	case 'Y':
> +		ptr = &remcomInBuffer[1];
> +		kgdb_hex2long(&ptr, &breakno);
> +		ptr++;
> +		kgdb_hex2long(&ptr, &breaktype);
> +		ptr++;
> +		kgdb_hex2long(&ptr, &length);
> +		ptr++;
> +		kgdb_hex2long(&ptr, &addr);
> +		if (set_hw_break(breakno & 0x3, breaktype & 0x3,
> +				 length & 0x3, addr) == 0) {
> +			strcpy(remcomOutBuffer, "OK");
> +		} else {
> +			strcpy(remcomOutBuffer, "ERROR");
> +		}
> +		break;
> +
> +		/* Remove hardware breakpoint */
> +	case 'y':
> +		ptr = &remcomInBuffer[1];
> +		kgdb_hex2long(&ptr, &breakno);
> +		if (remove_hw_break(breakno & 0x3) == 0) {
> +			strcpy(remcomOutBuffer, "OK");
> +		} else {
> +			strcpy(remcomOutBuffer, "ERROR");
> +		}
> +		break;
> +
> +	}		/* switch */
> +	return -1; /* this means that we do not want to exit from the handler */
> +}
> +
> +struct kgdb_arch arch_kgdb_ops =  {
> +	.gdb_bpt_instr = {0xcc},
> +	.flags = KGDB_HW_BREAKPOINT,
> +};
> --- clean.2.5/arch/i386/kernel/irq.c	2004-01-09 20:24:13.000000000 +0100
> +++ linux-mm/arch/i386/kernel/irq.c	2004-02-16 23:09:06.000000000 +0100
> @@ -410,7 +410,7 @@
>   * SMP cross-CPU interrupts have their own specific
>   * handlers).
>   */
> -asmlinkage unsigned int do_IRQ(struct pt_regs regs)
> +asmlinkage unsigned int do_IRQ(struct pt_regs *regs)
>  {
>  	/*
>  	 * We ack quickly, we don't want the irq controller
> @@ -422,7 +422,7 @@
>  	 * 0 return value means that this irq is already being
>  	 * handled by some other CPU. (or is disabled)
>  	 */
> -	int irq = regs.orig_eax & 0xff; /* high bits used in ret_from_ code  */
> +	int irq = regs->orig_eax & 0xff; /* high bits used in ret_from_ code  */
>  	irq_desc_t *desc = irq_desc + irq;
>  	struct irqaction * action;
>  	unsigned int status;
> @@ -488,7 +488,7 @@
>  		irqreturn_t action_ret;
>
>  		spin_unlock(&desc->lock);
> -		action_ret = handle_IRQ_event(irq, &regs, action);
> +		action_ret = handle_IRQ_event(irq, regs, action);
>  		spin_lock(&desc->lock);
>  		if (!noirqdebug)
>  			note_interrupt(irq, desc, action_ret);
> --- clean.2.5/arch/i386/kernel/nmi.c	2003-08-10 21:22:30.000000000 +0200
> +++ linux-mm/arch/i386/kernel/nmi.c	2004-02-16 23:09:06.000000000 +0100
> @@ -25,6 +25,7 @@
>  #include <linux/module.h>
>  #include <linux/nmi.h>
>  #include <linux/sysdev.h>
> +#include <linux/debugger.h>
>
>  #include <asm/smp.h>
>  #include <asm/mtrr.h>
> @@ -420,14 +421,25 @@
>  	int sum, cpu = smp_processor_id();
>
>  	sum = irq_stat[cpu].apic_timer_irqs;
> +	if (atomic_read(&debugger_active)) {
>
> -	if (last_irq_sums[cpu] == sum) {
> +		/*
> +		 * The machine is in debugger, hold this cpu if already
> +		 * not held.
> +		 */
> +		debugger_nmihook(cpu, regs);
> +		alert_counter[cpu] = 0;
> +
> +	} else if (last_irq_sums[cpu] == sum) {
>  		/*
>  		 * Ayiee, looks like this CPU is stuck ...
>  		 * wait a few IRQs (5 seconds) before doing the oops ...
>  		 */
>  		alert_counter[cpu]++;
>  		if (alert_counter[cpu] == 5*nmi_hz) {
> +
> +			CHK_DEBUGGER(2,SIGSEGV,0,regs,)
> +
>  			spin_lock(&nmi_print_lock);
>  			/*
>  			 * We are in trouble anyway, lets at least try
> --- clean.2.5/arch/i386/kernel/signal.c	2003-11-24 17:08:26.000000000 +0100
> +++ linux-mm/arch/i386/kernel/signal.c	2004-02-16 23:09:06.000000000 +0100
> @@ -580,7 +580,8 @@
>  		 * have been cleared if the watchpoint triggered
>  		 * inside the kernel.
>  		 */
> -		__asm__("movl %0,%%db7"	: : "r" (current->thread.debugreg[7]));
> +		if (current->thread.debugreg[7])
> +			__asm__("movl %0,%%db7"	: : "r" (current->thread.debugreg[7]));
>
>  		/* Whee!  Actually deliver the signal.  */
>  		handle_signal(signr, &info, oldset, regs);
> --- clean.2.5/arch/i386/kernel/traps.c	2003-10-18 20:26:27.000000000 +0200
> +++ linux-mm/arch/i386/kernel/traps.c	2004-02-16 23:09:06.000000000 +0100
> @@ -51,6 +51,7 @@
>
>  #include <linux/irq.h>
>  #include <linux/module.h>
> +#include <linux/debugger.h>
>
>  #include "mach_traps.h"
>
> @@ -256,6 +257,7 @@
>  {
>  	static int die_counter;
>
> +	CHK_DEBUGGER(1,SIGTRAP,err,regs,)
>  	console_verbose();
>  	spin_lock_irq(&die_lock);
>  	bust_spinlocks(1);
> @@ -330,6 +332,7 @@
>  #define DO_ERROR(trapnr, signr, str, name) \
>  asmlinkage void do_##name(struct pt_regs * regs, long error_code) \
>  { \
> +	CHK_DEBUGGER(trapnr,signr,error_code,regs,)\
>  	do_trap(trapnr, signr, str, 0, regs, error_code, NULL); \
>  }
>
> @@ -347,7 +350,10 @@
>  #define DO_VM86_ERROR(trapnr, signr, str, name) \
>  asmlinkage void do_##name(struct pt_regs * regs, long error_code) \
>  { \
> +	CHK_DEBUGGER(trapnr,signr,error_code,regs,goto skip_trap)\
>  	do_trap(trapnr, signr, str, 1, regs, error_code, NULL); \
> +skip_trap: \
> +	return; \
>  }
>
>  #define DO_VM86_ERROR_INFO(trapnr, signr, str, name, sicode, siaddr) \
> @@ -547,7 +553,7 @@
>  	tsk->thread.debugreg[6] = condition;
>
>  	/* Mask out spurious TF errors due to lazy TF clearing */
> -	if (condition & DR_STEP) {
> +	if (condition & DR_STEP && !debugger_step) {
>  		/*
>  		 * The TF error should be masked out only if the current
>  		 * process is not traced and if the TRAP flag has been set
> @@ -570,11 +576,13 @@
>  	info.si_errno = 0;
>  	info.si_code = TRAP_BRKPT;
>
> -	/* If this is a kernel mode trap, save the user PC on entry to
> -	 * the kernel, that's what the debugger can make sense of.
> -	 */
> -	info.si_addr = ((regs->xcs & 3) == 0) ? (void *)tsk->thread.eip :
> -	                                        (void *)regs->eip;
> +
> +	/* If this is a kernel mode trap, we need to reset db7 to allow us
> +	 * to continue sanely */
> +	if ((regs->xcs & 3) == 0)
> +		goto clear_dr7;
> +
> +	info.si_addr = (void *)regs->eip;
>  	force_sig_info(SIGTRAP, &info, tsk);
>
>  	/* Disable additional traps. They'll be re-enabled when
> @@ -584,6 +592,7 @@
>  	__asm__("movl %0,%%db7"
>
>  		: /* no output */
>  		: "r" (0));
>
> +	CHK_DEBUGGER(1,SIGTRAP,error_code,regs,)
>  	return;
>
>  debug_vm86:
> --- clean.2.5/arch/i386/mm/fault.c	2003-12-21 20:29:03.000000000 +0100
> +++ linux-mm/arch/i386/mm/fault.c	2004-02-16 23:09:06.000000000 +0100
> @@ -2,6 +2,11 @@
>   *  linux/arch/i386/mm/fault.c
>   *
>   *  Copyright (C) 1995  Linus Torvalds
> + *
> + *  Change History
> + *
> + *	Tigran Aivazian <tigran@sco.com>	Remote debugging support.
> + *
>   */
>
>  #include <linux/signal.h>
> @@ -21,6 +26,7 @@
>  #include <linux/vt_kern.h>		/* For unblank_screen() */
>  #include <linux/highmem.h>
>  #include <linux/module.h>
> +#include <linux/debugger.h>
>
>  #include <asm/system.h>
>  #include <asm/uaccess.h>
> @@ -399,6 +405,8 @@
>   	if (is_prefetch(regs, address))
>   		return;
>
> +	CHK_DEBUGGER(14, SIGSEGV,error_code, regs,)
> +
>  /*
>   * Oops. The kernel tried to access some bad page. We'll have to
>   * terminate things with extreme prejudice.
> --- clean.2.5/include/asm-i386/kgdb.h	2004-02-17 11:39:24.000000000 +0100
> +++ linux-mm/include/asm-i386/kgdb.h	2004-02-16 23:09:06.000000000 +0100
> @@ -0,0 +1,49 @@
> +#ifndef _ASM_KGDB_H_
> +#define _ASM_KGDB_H_
> +
> +/*
> + * Copyright (C) 2001-2004 Amit S. Kale
> + */
> +
> +#include <linux/ptrace.h>
> +
> +/* gdb locks */
> +#define KGDB_MAX_NO_CPUS 8
> +
> +/************************************************************************/
> +/* BUFMAX defines the maximum number of characters in inbound/outbound
> buffers*/ +/* at least NUMREGBYTES*2 are needed for register packets */
> +/* Longer buffer is needed to list all threads */
> +#define BUFMAX 1024
> +
> +/* Number of bytes of registers.  */
> +#define NUMREGBYTES 64
> +/*
> + *  Note that this register image is in a different order than
> + *  the register image that Linux produces at interrupt time.
> + *
> + *  Linux's register image is defined by struct pt_regs in ptrace.h.
> + *  Just why GDB uses a different order is a historical mystery.
> + */
> +enum regnames { _EAX,  /* 0 */
> +	_ECX,  /* 1 */
> +	_EDX,  /* 2 */
> +	_EBX,  /* 3 */
> +	_ESP,  /* 4 */
> +	_EBP,  /* 5 */
> +	_ESI,  /* 6 */
> +	_EDI,  /* 7 */
> +	_PC,   /* 8 also known as eip */
> +	_PS,   /* 9 also known as eflags */
> +	_CS,   /* 10 */
> +	_SS,   /* 11 */
> +	_DS,   /* 12 */
> +	_ES,   /* 13 */
> +	_FS,   /* 14 */
> +	_GS    /* 15 */
> +};
> +
> +#define BREAKPOINT() asm("   int $3");
> +#define BREAK_INSTR_SIZE       1
> +
> +#endif /* _ASM_KGDB_H_ */
> --- clean.2.5/include/asm-i386/processor.h	2004-01-09 20:24:24.000000000
> +0100 +++ linux-mm/include/asm-i386/processor.h	2004-02-16
> 23:09:06.000000000 +0100 @@ -425,6 +425,8 @@
>  	unsigned int		saved_fs, saved_gs;
>  /* IO permissions */
>  	unsigned long	*io_bitmap_ptr;
> +	void *		debuggerinfo;
> +
>  };
>
>  #define INIT_THREAD  {							\