139 lines
4.5 KiB
Markdown
139 lines
4.5 KiB
Markdown
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# Kernel Debugging
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## 1. Preparation
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### Set up a development environment:
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- Install a Linux distribution (e.g., Ubuntu, Fedora)
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- Install essential development tools: gcc, make, binutils, etc.
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- Download kernel source code from kernel.org
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### Configure kernel for debugging:
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- Enable CONFIG_DEBUG_INFO in kernel configuration
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- Enable CONFIG_KGDB for remote debugging
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- Enable other relevant debug options (e.g., CONFIG_DEBUG_KERNEL)
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### Build the kernel with debug symbols:
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```bash
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make menuconfig
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make -j$(nproc)
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```
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## 2. Kernel Debugging Techniques
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### Printk Debugging:
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- Use printk() function to add log messages
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- Set appropriate log levels (KERN_INFO, KERN_DEBUG, etc.)
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- View logs using dmesg or /var/log/kern.log
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### Kernel Oops and Panic Analysis:
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- Analyze oops messages in kernel logs
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- Use addr2line to translate addresses to source code lines
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- Examine call traces to identify the source of the problem
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### KGDB (Kernel GNU Debugger):
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- Configure a serial connection or network for remote debugging
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- Set up a GDB client on the host machine
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- Connect to the target machine running the kernel
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- Set breakpoints, step through code, and examine variables
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### Ftrace (Function Tracer):
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- Enable Ftrace in kernel configuration
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- Use trace-cmd tool to collect and analyze function call data
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- Examine function graph to understand kernel execution flow
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### Systemtap:
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- Write custom scripts to instrument the kernel
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- Collect detailed performance data and debug information
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- Analyze complex scenarios without modifying kernel source
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### Kernel Probes (Kprobes):
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- Insert dynamic breakpoints in the kernel
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- Gather debugging and performance information
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- Use jprobes for function entry probing and kretprobes for return probes
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## 3. Advanced Debugging Techniques
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### Memory Debugging:
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- Use KASAN (Kernel Address Sanitizer) to detect memory errors
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- Enable CONFIG_DEBUG_PAGEALLOC to catch use-after-free bugs
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- Utilize SLUB debug features for slab allocator issues
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### Lockdep (Lock Dependency) Checker:
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- Enable CONFIG_PROVE_LOCKING and CONFIG_DEBUG_LOCKDEP
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- Detect potential deadlocks and incorrect locking behavior
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- Analyze lock dependency graphs
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### RCU (Read-Copy-Update) Debugging:
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- Enable CONFIG_RCU_TRACE for RCU tracing
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- Use rcutorture module to stress-test RCU implementations
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- Analyze RCU grace period and callback execution
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### Kernel Live Patching:
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- Use kpatch or livepatch to apply runtime fixes
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- Debug issues related to live patching mechanisms
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- Verify patch consistency and function replacement
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## 4. Tools and Utilities
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### Crash utility:
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- Analyze kernel core dumps
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- Examine kernel data structures and memory
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- Useful for post-mortem analysis of kernel panics
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### Perf:
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- Profile kernel and user space performance
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- Identify hotspots and performance bottlenecks
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- Analyze hardware events and software tracepoints
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### eBPF (extended Berkeley Packet Filter):
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- Write eBPF programs for advanced tracing and debugging
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- Use bpftrace for one-liners and short scripts
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- Develop custom eBPF tools for specific debugging needs
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### Kdump:
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- Configure and enable kernel crash dump mechanism
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- Capture memory dumps on kernel panics
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- Analyze dumps using crash utility or GDB
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## 5. Best Practices
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### Use git for version control:
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- Maintain a clean development history
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- Utilize git bisect for identifying problematic commits
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### Maintain a test environment:
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- Use virtual machines or dedicated hardware for testing
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- Set up automated testing frameworks (e.g., KernelCI)
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### Collaborate with the community:
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- Subscribe to relevant mailing lists (e.g., LKML)
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- Share and discuss issues on appropriate forums
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- Submit well-formatted patch series for review
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### Document your findings:
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- Maintain detailed notes of debugging sessions
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- Create reproducible test cases for bugs
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- Write clear bug reports and patch descriptions
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## 6. Debugging Real-world Scenarios
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### Boot issues:
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- Use early printk for early boot problems
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- Analyze initcall debugging output
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- Utilize kernel command line parameters for troubleshooting
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### Device driver debugging:
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- Use debugfs to expose driver information
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- Implement IOCTL commands for debugging
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- Utilize kernel's tracepoints in the driver code
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### File system issues:
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- Enable verbose mount options
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- Use debugfs to examine file system internals
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- Analyze block layer tracing for I/O related problems
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### Network stack debugging:
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- Use network sniffer tools (e.g., tcpdump, Wireshark)
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- Enable netconsole for remote kernel debugging
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- Analyze netfilter and netlink debugging information
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