The simplest thing to do is to run the program in gdb and follow through until it segfaults. When your program crashes, GDB will step up and tell you what line it crashed on. Usually it will be a line where the program was trying to manipulate some memory-mangled variable.
You can use bt or backtrace to figure out where you are in the stack, and then p or print to look at the variables and see if any of them have stepped outside their bounds or are full of garbage. As a shortcut, you can gdb your program and then load the corefile to get directly to the crash. Infinite loops are another bug that are hard to hunt down on your own, but simple to find with GDB.
Load up your program in GDB, and run it until you get to the loop. Then hit control-C to force your way back to the GDB prompt. Type bt and you'll be told what line you're on. Use list to look at the code and see if you can figure out what's causing the loop.
If you can't, use n or next to progress through the loop one line at a time, all the while using p to inspect your counter variable. Most bugs aren't so simply categorized; often your program will provide the wrong output for no apparent reason.
There are a few techniques that can come in handy when you have this sort of problem. One thing you can do is set a breakpoint right after your program asks for input, then next your way along, looking periodically at the stack and the variables to make sure that everything is going according to plan. If you think the problem is due to the value of a particular variable and your code is hard to follow, you can watch that variable.
Here follows a transcript of a GDB session with a program intended to parse regular expressions this program was originally called rep. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "alphaevdec-osf4.
Let's skip toward the bottom, where we'll see some of my actual code:. Program exited normally. I don't have enough time write it by myself. Aviv Shabtay , Peng Kai , software engineering at seeyon software. Sungwon Park. Phan Hien , Contributor at Fedora Tags gdb. Junhui Shao , Software Engineer at Renren. Show More.
Views Total views. Actions Shares. No notes for slide. Advanced Debugging with GDB 1. Advanced Debugging with gdbDavid KhosidSept 21, david. TAB completion. Executes all commands from system init file 2. Process command line options and operands 4. Executes all the commands from. Reads the command history recorded in the history file. How to see macros? A3: With set args command: gdb set args arg1 arg2 gdb show args set args without arguments — removes all arguments.
A1: file core. Total views 11, On Slideshare 0. From embeds 0. After that day, I felt like I was 10x faster at debugging the Pebble firmware and our suite of unit tests. I even had a new. Although there might be debuggers and interfaces out there that provide better experiences than using GDB directly, many of them are built on top of GDB and provide raw access to the GDB shell, where you can build and use automation through the Python scripting API.
At the end of most of the sections, there are links to either subpages with the GDB manual or to the original content to learn more about the topic discussed. Like Interrupt? Subscribe to get our latest posts straight to your mailbox.
First, we need to cover the items which I feel are most important for any developer or team to work efficiently within GDB. By default GDB does not save any history of the commands that were run during each session. To fix this, we can place the following in our. This could be in a bash script debug. This ensures that everyone working on the project has the latest set of configuration flags and GDB Python scripts to accelerate their debugging.
The first thing to talk about is how best to view and navigate the source code while debugging. Many times, the CI system builds with absolute paths instead of paths relative to the project root, which causes GDB not to be able to find the source files. If you want to patch it up now in GDB, you can use a combination of the set substitute-path and directory commands in GDB, depending on how the paths are built.
To fix the above issue, all I needed to do was to add a local directory. After adding it, GDB can find the source code of the line in the frame. Sometimes, you just want to quickly add a few lines above and below the current line. To quickly view ten lines of source-code context within GDB, you can use the list command. If you want to set a larger or smaller default number of lines shown with this command, you can change the setting:.
If you want something more powerful than disassemble , you can use objdump itself. There are many visual interfaces that are built into or on top of GDB. This should give you the source code viewer. You are now able to type next , step , continue , etc. You can print the register values within GDB using info registers. Notice these are the same values as above when we used info registers. If your gdbserver supports it, you can also set these register values! This is really useful for when you are trying to debug a hard fault and all you have are the sp , lr , and pc registers.
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