gdb_stub.c File Reference

Architecture-independent parts of in-kernel GDB stub. More...

Macros
#define	DEBUG_ENABLED   true
	Flag. Enables debug messages from the stub itself.
#define	DEBUG(...)
	Quick-and-dirty debug message macro.
#define	BUFMAX   512
	Defines the maximum number of characters in in/outbound buffers. More...

Functions
void	gdb_stub_entry (int signal_code, char *OPT NTS init_message)
	Generic entry point to the GDB stub. More...

Detailed Description

Architecture-independent parts of in-kernel GDB stub.

This file implements the kernel-side GDB stubs for remote debugging when running on hardware. It is loosely based on the public domain i386-stub.c which is part of the GDB sources.

The following gdb commands are supported:

command	function	Return value
?	What was the last sigval ?	SNN (signal NN)
g	return the value of the CPU registers	hex data or ENN
G	set the value of the CPU registers	OK or ENN
p	read the value of a single CPU register	hex data or ENN
P	set the value of a single CPU register	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
D	GDB detached – attempt to resume	(no reply)
k	kill – reboots the system	(no reply)

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 mod-256 sum of <packet info>

When a packet is received, it is first acknowledged with either '+' or '-'. '+' indicates a successful transfer. '-' indicates a failed transfer.

Example:

• Host: $m0,10#2a
• Reply: +$00010203040506070809101112131415#42

Macro Definition Documentation

#define BUFMAX   512

Defines the maximum number of characters in in/outbound buffers.

At least NUMREGBYTES * 2 are needed for register packets.

Function Documentation

void gdb_stub_entry	(	int	signal_code,
		char *OPT NTS	init_message
	)

Generic entry point to the GDB stub.

Wait for a remote GDB to start talking to us, and then service its requests. This function should run on a different stack the main kernel, and does not return.

Parameters

signal_code	Unix-style signal value indicating reason for interruption
init_message	Optional initial message to send to the remote GDB