Debugging with GDB: IPA Protocol Objects

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30.1.1 IPA Protocol Objects

The commands sent to and results received from agent may contain some complex data types called objects.

The in-process agent is running on the same machine with GDB or GDBserver, so it doesn’t have to handle as much differences between two ends as remote protocol (see Remote Protocol) tries to handle. However, there are still some differences of two ends in two processes:

1. word size. On some 64-bit machines, GDB or GDBserver can be compiled as a 64-bit executable, while in-process agent is a 32-bit one.
2. ABI. Some machines may have multiple types of ABI, GDB or GDBserver is compiled with one, and in-process agent is compiled with the other one.

Here are the IPA Protocol Objects:

1. agent expression object. It represents an agent expression (see Agent Expressions).
2. tracepoint action object. It represents a tracepoint action (see Tracepoint Action Lists) to collect registers, memory, static trace data and to evaluate expression.
3. tracepoint object. It represents a tracepoint (see Tracepoints).

The following table describes important attributes of each IPA protocol object:

Name	Size	Description
agent expression object
length	4	length of bytes code
byte code	length	contents of byte code
tracepoint action for collecting memory
’M’	1	type of tracepoint action
addr	8	if basereg is ‘-1’, addr is the address of the lowest byte to collect, otherwise addr is the offset of basereg for memory collecting.
len	8	length of memory for collecting
basereg	4	the register number containing the starting memory address for collecting.
tracepoint action for collecting registers
’R’	1	type of tracepoint action
tracepoint action for collecting static trace data
’L’	1	type of tracepoint action
tracepoint action for expression evaluation
’X’	1	type of tracepoint action
agent expression	length of	agent expression object
tracepoint object
number	4	number of tracepoint
address	8	address of tracepoint inserted on
type	4	type of tracepoint
enabled	1	enable or disable of tracepoint
step_count	8	step
pass_count	8	pass
numactions	4	number of tracepoint actions
hit count	8	hit count
trace frame usage	8	trace frame usage
compiled_cond	8	compiled condition
orig_size	8	orig size
condition	4 if condition is NULL otherwise length of agent expression object	zero if condition is NULL, otherwise is agent expression object
actions	variable	numactions number of tracepoint action object

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