GDB debugging manual, one article is enough

1. Introduction to GDB

GDB is: a debugging tool under UNIX and UNIX-like . Perhaps, you prefer the graphical interface method, such as VC, BCB and other IDE debugging, but if you are doing software under the UNIX platform, you will find that the advantage of the GDB debugging tool compared with VC and z is that it can repair Functions such as network breakpoints and link recovery are more powerful than BCB's graphical debugger. The so-called "the ruler is short, the inch is long" is the truth.

Two, function

Generally speaking, GDB mainly helps you complete the following four functions:

1. Start your program, and you can run the program as you like according to your custom requirements.

2. Allow the program being debugged to stop at the breakpoint you specify. (Breakpoints can be conditional expressions )

3. When the program is stopped, you can check what happened in your program at this time.

4. You can change your program to correct the impact of a BUG to test other BUGs.

3. Manual

When using GDB to debug a program, there are two points to note:

1. To use GDB to debug a program, the program must be compiled with the compile option -g, otherwise the program does not contain debugging information;

2. The GCC compiler supports -O and -g to participate in compilation together.

1. GDB debugging mainly has three methods:

1. Debug the target program directly: gdb ./hello_server
2. Attach process id: gdb attach pid
3. Debug core file: gdb filename corename

2. Exit GDB

• You can use the command: q (abbreviation for quit) or Ctr + d  to exit GDB.
• If GDB attaches a process, use the command  detach  to detach the attached process before exiting GDB.

3. Common commands

Frequently used commands are usually abbreviated.

command name	command abbreviation	command description
run	r	run a program to be debugged
continue	c	Resume a suspended program
next	n	run to the next line
step	s	Single-step execution, when encountering a function, it will enter
until	u	Run to the specified line and stop
finish	fi	End the current calling function and return to the previous calling function
return	return	End the current calling function and return the specified value to the previous function call
jump	j	Jump the current program execution flow to the specified line or address
print	p	print variable or register value
backtrace	bt	View the call stack of the current thread
frame	f	switch to the specified stack of the current calling thread
thread	thread	Switch to the specified thread
break	b	add breakpoint
tbreak	tb	Add a temporary breakpoint
delete	d	delete breakpoint
enable	enable	enable a breakpoint
disable	disable	disable a breakpoint
watch	watch	Monitor whether the value of a variable or memory address changes
list	l	show source code
info	i	View information such as breakpoints/threads
ptype	ptype	View variable type
disassemble	dis	View assembly code
set args	set args	Set program startup command line parameters
show args	show args	View the command line parameters set

 4. Example of use

 1. Use gdb+ program name to directly start GDB debugging

gdb test

2. Use set args to set the startup parameters because there are multiple startup parameters, so it is args

set args parameter1 parameter2 parameter3 ...

 

3. Use the b command to break the point

b avformat_find_stream_info (directly hit the function name breakpoint)

b 2440 (hit the specified line number breakpoint in the current file)

b main (set a breakpoint at the main function)

The b command will automatically find the corresponding function name, and tell you how many lines in which file to set a breakpoint 

4. Use the r command to run the program

r (the program will run to the breakpoint)

Run to the first breakpoint Breakpoint 1

5. Use the c command to run to the next breakpoint

 Breakpoint 2, avformat_find_stream_info

6. Use the s and n commands to execute step by step or to the next line

s

n

 

7. Use quit to exit GDB debugging

(If the GDB program is running, use ctrl+C to interrupt)

quit
 

The program is exited by kill, enter y (yes) to exit GDB debugging! 

 

 That's it.

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