Use of GDB

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Preface

GDB By GNU Debugging tools provided by the software system community , Same as GCC It forms a complete development environment ,GDB yes Linux And many classes Unix Standard development environment in the system .
Generally speaking ,GDB It mainly helps you complete the following four functions ：

1. Start the program , You can run the program at will according to custom requirements （ Start the program )
2. Allows the debugged program to stop at the specified set breakpoint （ Use breakpoints to stop programs , Breakpoints can be conditional expressions ）
3. When the program is stopped , You can check what happens in the program at this time （ Check the variables in the program at this time ）
4. You can change the program , Will a BUG The impact is corrected to test other BUG( Change the program )

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One 、GDB Commissioning preparations

1. When compiling for debugging , We'll turn off the compiler's optimization options -O
2. Turn on debug options -g
3. in addition ,-Wall The option turns on all... Without affecting the behavior of the program as much as possible warning, Many problems can also be found , Avoid unnecessary BUG（ Or you can skip it ）.

gcc -g -Wall program.c -o program

Be careful ：
-g Option is used to add source code information to the executable , For example, the number of machine instructions in the executable file corresponds to the number of lines of the source code , But it's not embedding the entire source file into the executable , So when debugging Must ensure gdb Can find source file .

Two 、GDB The order of

install GDB Debugging tools ,apt-get -y install gdb

• Start and exit

gdb  Executable program   // start-up 
quit  perhaps  q  // sign out 

• Set parameters for the program / Get and set parameters (main Parameters in function )

set args 10 20 // Set parameters 
show args  // Get and set parameters 

• GDB Use the help help

• View the current file code

	list/l （ Show... From default location ）
	list/l  Line number  （ Displays... From the specified line ）
	list/l  Function name （ Displays... From the specified function ）

• View non current file code

	list/l  file name : Line number 
	list/l  file name : Function name 

• Set the number of rows displayed

show list/listsize
set list/listsize  Row number 

Two 、GDB The breakpoint of

• To set breakpoints

b/break  Line number 
b/break  Function name 
b/break  file name : Line number 
b/break  file name : function 

• View breakpoints

i/info b/break

• Delete breakpoints , This place is not a line number , Is the breakpoint in the breakpoint information （i b） Number in , After deleting the breakpoint , The breakpoint number will not be updated , If it was 4, The number of the new next breakpoint will be 5.

d/del/delete  Breakpoint number 

• Setting breakpoint is invalid

dis/disable  Breakpoint number 

• Setting breakpoints takes effect

ena/enable  Breakpoint number 

• Set conditional breakpoints （ It is generally used in the position of circulation ）

b/break 10 if i=5

Two 、GDB Debugging of

• function GDB Program

start（ Stop on the first line ）
run（ After program running , Stop when you encounter the first breakpoint ）

• Continue operation , Stop at the next breakpoint

c/continue

• One line down （ Will not enter function body ）

n/next

• Variable operating

p/print  Variable name （ Print variable values ）
ptype  Variable name （ Print variable types ）

• Step down debugging （ Encountered a function entering the function body ）, When you jump out of a function , There is no breakpoint in the function , Otherwise, the next execution will stop at the breakpoint .

s/step
finish（ Jump out of the body of functions ）

Automatic variable operation

display  Variable name （ Automatically print the value of the specified variable , Otherwise, perform the next step every time , Both  print  Primary variable ）
i/info display
undisplay  Number （i display Number in ）

• Other operating , When jumping out of the loop, first jump to the beginning of the loop （while()、for()）, And there are no breakpoints in the loop , Otherwise, the next execution will stop at the breakpoint .

set var  Variable name = A variable's value  （ More used in the loop ）
until （ Out of the loop ）

• Multi process and multi thread debugging

// Switch multithreading  thread id
// Switch multithreading  inferior id

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summary

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