GDB common commands

GDB It mainly completes the following four functions ：

• Start your program , You can run the program according to your custom requirements .
• You can make the debugged program stop at the breakpoint you specified .（ Breakpoints can be conditional expressions ）
• When the program is stopped , You can check what's going on in your program at this point .
• Dynamically change the execution environment of your program .

Common commands ：

A good blog

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Linux How to use gdb debugging core file

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1.core file

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core Files are in the running state of the program Memory Image appears when the program is running segmentation fault（core dumped） When it's wrong , The program stops running , And produce core file .

Use gdb debugging core Files can help us quickly locate the program Segment error The location of . Executable programs should be compiled with -g Compilation options , Generate debugging information .
When the memory accessed by the program exceeds the memory space given by the system , It will produce Segmentation fault(core dumped), therefore , The main situations of segment errors are ：

1. Access to non-existent memory address
2. Access system protected memory address
3. Array access out of bounds, etc
   core dumped It's also called core dump , When an exception occurs while the program is running , When the program exits abnormally , The operating system stores the current memory status of the program in a core In file .
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2. control core Whether the file is generated

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1. Use ulimit -c The command can be viewed core File generation switch . If the result is 0, This function is turned off , Will not generate core file .
2. Use ulimit -c filesize command , Can restrict core File size （filesize The unit is kb）. If the generated information exceeds this size , Will be cut , In the end, the process is incomplete core file . example ：ulimit -c 1024
3. Use ulimit -c unlimited said core Unlimited file size .
4. By command at the terminal ulimit -c unlimited It's just a temporary change , Invalid after restart , There are three ways to permanently modify .

5.  stay /etc/rc.local Add a line to the list ulimit -c unlimited
    stay /etc/profile Add a line to the list ulimit -c unlimited
   
       
        
   
       
        
   
         
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3.core File name and build path

core The default file name is core.pid,pid It refers to the process number of the program that generated the segment error .

The default path is the current directory of the program that generated the segment error .

modify core File name and path

4.gdb debugging core Document steps

Use gdb debugging core File to find the location of the segment error in the program , Need executable program plus -g Compile command options .
The common ones are the following （ Recommend the first ）：
Step one ：
（1） start-up gdb Get into core file , Command format ：gdb [exec file] [ core file]
example ：gdb ./test test.core
（2） After entering , Find segment error location ：where perhaps bt
You can locate the specific location of specific files in the source program , A segment error occurred .
Step two ：
（1） start-up gdb Get into core file , Command format ：gdb -core=[core file]
example ：gdb -core=test.core
（2） When entering gdb after , Appoint core Symbol table corresponding to the file , Command format ：file [exec file]

 stay gdb Input bt command    When encountering segment errors , Input bt command , You can track errors 

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