gdb-stub.c

上传linux-jx2410的源代码

/*
 *  arch/mips/kernel/gdb-stub.c
 *
 *  Originally written by Glenn Engel, Lake Stevens Instrument Division
 *
 *  Contributed by HP Systems
 *
 *  Modified for SPARC by Stu Grossman, Cygnus Support.
 *
 *  Modified for Linux/MIPS (and MIPS in general) by Andreas Busse
 *  Send complaints, suggestions etc. to <[e-mail]>
 *
 *  Copyright (C) 1995 Andreas Busse
 *
 * $Id: gdb-stub.c,v 1.1.1.1 2004/02/04 12:55:40 laputa Exp $
 */

/*
 *  To enable debugger support, two things need to happen.  One, a
 *  call to set_debug_traps() is necessary in order to allow any breakpoints
 *  or error conditions to be properly intercepted and reported to gdb.
 *  Two, a breakpoint needs to be generated to begin communication.  This
 *  is most easily accomplished by a call to breakpoint().  Breakpoint()
 *  simulates a breakpoint by executing a BREAK instruction.
 *
 *
 *    The following gdb commands are supported:
 *
 * command          function                               Return value
 *
 *    g             return the value of the CPU registers  hex data or ENN
 *    G             set the value of the CPU registers     OK or ENN
 *
 *    mAA..AA,LLLL  Read LLLL bytes at address AA..AA      hex data or ENN
 *    MAA..AA,LLLL: Write LLLL bytes at address AA.AA      OK or ENN
 *
 *    c             Resume at current address              SNN   ( signal NN)
 *    cAA..AA       Continue at address AA..AA             SNN
 *
 *    s             Step one instruction                   SNN
 *    sAA..AA       Step one instruction from AA..AA       SNN
 *
 *    k             kill
 *
 *    ?             What was the last sigval ?             SNN   (signal NN)
 *
 *    bBB..BB	    Set baud rate to BB..BB		   OK or BNN, then sets
 *							   baud rate
 *
 * All commands and responses are sent with a packet which includes a
 * checksum.  A packet consists of
 *
 * $<packet info>#<checksum>.
 *
 * where
 * <packet info> :: <characters representing the command or response>
 * <checksum>    :: < two hex digits computed as modulo 256 sum of <packetinfo>>
 *
 * When a packet is received, it is first acknowledged with either '+' or '-'.
 * '+' indicates a successful transfer.  '-' indicates a failed transfer.
 *
 * Example:
 *
 * Host:                  Reply:
 * $m0,10#2a               +$00010203040506070809101112131415#42
 *
 * 
 *  ==============
 *  MORE EXAMPLES:
 *  ==============
 *
 *  For reference -- the following are the steps that one
 *  company took (RidgeRun Inc) to get remote gdb debugging
 *  going. In this scenario the host machine was a PC and the
 *  target platform was a Galileo EVB64120A MIPS evaluation
 *  board.
 *   
 *  Step 1:
 *  First download gdb-5.0.tar.gz from the internet.
 *  and then build/install the package.
 * 
 *  Example:
 *    $ tar zxf gdb-5.0.tar.gz
 *    $ cd gdb-5.0
 *    $ ./configure --target=mips-linux-elf
 *    $ make
 *    $ install
 *    $ which mips-linux-elf-gdb
 *    /usr/local/bin/mips-linux-elf-gdb
 * 
 *  Step 2:
 *  Configure linux for remote debugging and build it.
 * 
 *  Example:
 *    $ cd ~/linux
 *    $ make menuconfig <go to "Kernel Hacking" and turn on remote debugging>
 *    $ make dep; make vmlinux
 * 
 *  Step 3:
 *  Download the kernel to the remote target and start
 *  the kernel running. It will promptly halt and wait 
 *  for the host gdb session to connect. It does this
 *  since the "Kernel Hacking" option has defined 
 *  CONFIG_REMOTE_DEBUG which in turn enables your calls
 *  to:
 *     set_debug_traps();
 *     breakpoint();
 * 
 *  Step 4:
 *  Start the gdb session on the host.
 * 
 *  Example:
 *    $ mips-linux-elf-gdb vmlinux
 *    (gdb) set remotebaud 115200
 *    (gdb) target remote /dev/ttyS1
 *    ...at this point you are connected to 
 *       the remote target and can use gdb
 *       in the normal fasion. Setting 
 *       breakpoints, single stepping,
 *       printing variables, etc.
 *
 */

#include <linux/string.h>
#include <linux/kernel.h>
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/console.h>
#include <linux/init.h>

#include <asm/asm.h>
#include <asm/mipsregs.h>
#include <asm/pgtable.h>
#include <asm/system.h>
#include <asm/gdb-stub.h>
#include <asm/inst.h>

/*
 * external low-level support routines
 */

extern int putDebugChar(char c);    /* write a single character      */
extern char getDebugChar(void);     /* read and return a single char */
extern void trap_low(void);

/*
 * breakpoint and test functions
 */
extern void breakpoint(void);
extern void breakinst(void);
extern void adel(void);

/*
 * local prototypes
 */

static void getpacket(char *buffer);
static void putpacket(char *buffer);
static int computeSignal(int tt);
static int hex(unsigned char ch);
static int hexToInt(char **ptr, int *intValue);
static unsigned char *mem2hex(char *mem, char *buf, int count, int may_fault);
void handle_exception(struct gdb_regs *regs);

/*
 * BUFMAX defines the maximum number of characters in inbound/outbound buffers
 * at least NUMREGBYTES*2 are needed for register packets
 */
#define BUFMAX 2048

static char input_buffer[BUFMAX];
static char output_buffer[BUFMAX];
static int initialized;	/* !0 means we've been initialized */
static const char hexchars[]="0123456789abcdef";

/* Used to prevent crashes in memory access.  Note that they'll crash anyway if
   we haven't set up fault handlers yet... */
int kgdb_read_byte(unsigned *address, unsigned *dest);
int kgdb_write_byte(unsigned val, unsigned *dest);

/*
 * Convert ch from a hex digit to an int
 */
static int hex(unsigned char ch)
{
	if (ch >= 'a' && ch <= 'f')
		return ch-'a'+10;
	if (ch >= '0' && ch <= '9')
		return ch-'0';
	if (ch >= 'A' && ch <= 'F')
		return ch-'A'+10;
	return -1;
}

/*
 * scan for the sequence $<data>#<checksum>
 */
static void getpacket(char *buffer)
{
	unsigned char checksum;
	unsigned char xmitcsum;
	int i;
	int count;
	unsigned char ch;

	do {
		/*
		 * wait around for the start character,
		 * ignore all other characters
		 */
		while ((ch = (getDebugChar() & 0x7f)) != '$') ;

		checksum = 0;
		xmitcsum = -1;
		count = 0;
	
		/*
		 * now, read until a # or end of buffer is found
		 */
		while (count < BUFMAX) {
			ch = getDebugChar() & 0x7f;
			if (ch == '#')
				break;
			checksum = checksum + ch;
			buffer[count] = ch;
			count = count + 1;
		}

		if (count >= BUFMAX)
			continue;

		buffer[count] = 0;

		if (ch == '#') {
			xmitcsum = hex(getDebugChar() & 0x7f) << 4;
			xmitcsum |= hex(getDebugChar() & 0x7f);

			if (checksum != xmitcsum)
				putDebugChar('-');	/* failed checksum */
			else {
				putDebugChar('+'); /* successful transfer */

				/*
				 * if a sequence char is present,
				 * reply the sequence ID
				 */
				if (buffer[2] == ':') {
					putDebugChar(buffer[0]);
					putDebugChar(buffer[1]);

					/*
					 * remove sequence chars from buffer
					 */
					count = strlen(buffer);
					for (i=3; i <= count; i++)
						buffer[i-3] = buffer[i];
				}
			}
		}
	}
	while (checksum != xmitcsum);
}

/*
 * send the packet in buffer.
 */
static void putpacket(char *buffer)
{
	unsigned char checksum;
	int count;
	unsigned char ch;

	/*
	 * $<packet info>#<checksum>.
	 */

	do {
		putDebugChar('$');
		checksum = 0;
		count = 0;

		while ((ch = buffer[count]) != 0) {
			if (!(putDebugChar(ch)))
				return;
			checksum += ch;
			count += 1;
		}

		putDebugChar('#');
		putDebugChar(hexchars[checksum >> 4]);
		putDebugChar(hexchars[checksum & 0xf]);

	}
	while ((getDebugChar() & 0x7f) != '+');
}


/*
 * Convert the memory pointed to by mem into hex, placing result in buf.
 * Return a pointer to the last char put in buf (null), in case of mem fault,
 * return 0.
 * may_fault is non-zero if we are reading from arbitrary memory, but is currently
 * not used.
 */
static unsigned char *mem2hex(char *mem, char *buf, int count, int may_fault)
{
	unsigned char ch;

	while (count-- > 0) {
		if (kgdb_read_byte(mem++, &ch) != 0)
			return 0;
		*buf++ = hexchars[ch >> 4];
		*buf++ = hexchars[ch & 0xf];
	}

	*buf = 0;

	return buf;
}

/*
 * convert the hex array pointed to by buf into binary to be placed in mem
 * return a pointer to the character AFTER the last byte written
 * may_fault is non-zero if we are reading from arbitrary memory, but is currently
 * not used.
 */
static char *hex2mem(char *buf, char *mem, int count, int may_fault)
{
	int i;
	unsigned char ch;

	for (i=0; i<count; i++)
	{
		ch = hex(*buf++) << 4;
		ch |= hex(*buf++);
		if (kgdb_write_byte(ch, mem++) != 0)
			return 0;
	}

	return mem;
}

/*
 * This table contains the mapping between SPARC hardware trap types, and
 * signals, which are primarily what GDB understands.  It also indicates
 * which hardware traps we need to commandeer when initializing the stub.
 */
static struct hard_trap_info {
	unsigned char tt;		/* Trap type code for MIPS R3xxx and R4xxx */
	unsigned char signo;		/* Signal that we map this trap into */
} hard_trap_info[] = {
	{ 6, SIGBUS },			/* instruction bus error */
	{ 7, SIGBUS },			/* data bus error */
	{ 9, SIGTRAP },			/* break */
	{ 10, SIGILL },			/* reserved instruction */
/*	{ 11, SIGILL },		*/	/* CPU unusable */
	{ 12, SIGFPE },			/* overflow */
	{ 13, SIGTRAP },		/* trap */
	{ 14, SIGSEGV },		/* virtual instruction cache coherency */
	{ 15, SIGFPE },			/* floating point exception */
	{ 23, SIGSEGV },		/* watch */
	{ 31, SIGSEGV },		/* virtual data cache coherency */
	{ 0, 0}				/* Must be last */
};

/* Save the normal trap handlers for user-mode traps. */
void *saved_vectors[32];

/*
 * Set up exception handlers for tracing and breakpoints
 */
void set_debug_traps(void)
{
	struct hard_trap_info *ht;
	unsigned long flags;
	unsigned char c;

	save_and_cli(flags);
	for (ht = hard_trap_info; ht->tt && ht->signo; ht++)
		saved_vectors[ht->tt] = set_except_vector(ht->tt, trap_low);
  
	putDebugChar('+'); /* 'hello world' */
	/*
	 * In case GDB is started before us, ack any packets
	 * (presumably "$?#xx") sitting there.
	 */
	while((c = getDebugChar()) != '$');
	while((c = getDebugChar()) != '#');
	c = getDebugChar(); /* eat first csum byte */
	c = getDebugChar(); /* eat second csum byte */
	putDebugChar('+'); /* ack it */

	initialized = 1;
	restore_flags(flags);
}

/*
 * Convert the MIPS hardware trap type code to a Unix signal number.
 */
static int computeSignal(int tt)
{
	struct hard_trap_info *ht;

	for (ht = hard_trap_info; ht->tt && ht->signo; ht++)
		if (ht->tt == tt)
			return ht->signo;

	return SIGHUP;		/* default for things we don't know about */
}

/*
 * While we find nice hex chars, build an int.
 * Return number of chars processed.
 */
static int hexToInt(char **ptr, int *intValue)
{
	int numChars = 0;
	int hexValue;

	*intValue = 0;

	while (**ptr) {
		hexValue = hex(**ptr);
		if (hexValue < 0)
			break;

		*intValue = (*intValue << 4) | hexValue;
		numChars ++;

		(*ptr)++;
	}

	return (numChars);
}


#if 0
/*
 * Print registers (on target console)
 * Used only to debug the stub...
 */
void show_gdbregs(struct gdb_regs * regs)
{
	/*
	 * Saved main processor registers
	 */
	printk("$0 : %08lx %08lx %08lx %08lx %08lx %08lx %08lx %08lx\n",
	       regs->reg0, regs->reg1, regs->reg2, regs->reg3,
               regs->reg4, regs->reg5, regs->reg6, regs->reg7);
	printk("$8 : %08lx %08lx %08lx %08lx %08lx %08lx %08lx %08lx\n",
	       regs->reg8, regs->reg9, regs->reg10, regs->reg11,
               regs->reg12, regs->reg13, regs->reg14, regs->reg15);
	printk("$16: %08lx %08lx %08lx %08lx %08lx %08lx %08lx %08lx\n",
	       regs->reg16, regs->reg17, regs->reg18, regs->reg19,
               regs->reg20, regs->reg21, regs->reg22, regs->reg23);
	printk("$24: %08lx %08lx %08lx %08lx %08lx %08lx %08lx %08lx\n",
	       regs->reg24, regs->reg25, regs->reg26, regs->reg27,
	       regs->reg28, regs->reg29, regs->reg30, regs->reg31);

	/*
	 * Saved cp0 registers
	 */
	printk("epc  : %08lx\nStatus: %08lx\nCause : %08lx\n",
	       regs->cp0_epc, regs->cp0_status, regs->cp0_cause);
}
#endif /* dead code */

/*
 * We single-step by setting breakpoints. When an exception
 * is handled, we need to restore the instructions hoisted
 * when the breakpoints were set.
 *
 * This is where we save the original instructions.
 */
static struct gdb_bp_save {
	unsigned int addr;
        unsigned int val;
} step_bp[2];

#define BP 0x0000000d  /* break opcode */

/*
 * Set breakpoint instructions for single stepping.
 */