Related concepts of GDB in embedded system

1. background

​ Debugger plays a very important role in embedded development , Download program 、 Single step debugging program 、 Lower breakpoint 、 Check the function call relationship through the function call stack . Usually we don't care about how the debugger works , Just debug , But the recognition of underlying principles is very important , This article will open a large piece of knowledge puzzle .

2. GDB What is it?

​ I understand , Not according to the official explanation , what GNU Plan something .GDB yes gcc A debugging program of tool chain , Notice the procedure .

3. GDB Two concepts of

​ GDB It's the program , The debugger is just running GDB Embedded tools for programs , In debugger GDB Procedures are often called GDB Server, seeing the name of a thing one thinks of its function , That's it. GDB The server . The server serves the client , Always listen for requests from clients . therefore ,PC There must be a GDB Client Client program .

​ Frequently used Jlink,ST-link Etc , Usually use your own gdb server The program runs on it , therefore , We usually use on-chip JTAG Interface ,SWD Interface to the debugger , After connecting , We are IDE Click the bug button on the to debug the board , here ,IDE Integrated in GDB Client,IDE Through this Client And ST-link perhaps Jlink Medium Server Communications , For example, send a breakpoint instruction （ stay IDE Click to show a red circle ）, Then run at full speed ,Client Will send the command to run at full speed to Server, here Server Send the signal to the internal debugging unit of the chip through the actual DuPont line , The chip runs .

4. GDB Serial protocol

​ Usually we use the debugger to connect the development board , such Client And Server It is difficult to observe the commands sent between , therefore , Can pass qemu The way , Give Way qemu function Server Program and start the network protocol stack ,Client Connect through the network Server To debug Server End of the code , such , Through the bag capturing tool Client And Server The interactive data between them is caught , You can know what they have said between them .

5. GDB Relevant command

gdb xxx.elf  // client  End load symbol table 

target remote ip:port //  Connect  Server
    
load xxx.elf //  take  elf load  To  Server  End , It is equivalent to downloading the program again for the board 

b xxx //  stay xxx  Break point 
    
c //  Run at full speed , Stop at breakpoint 

bt //  Display function call stack 
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