I am analyzing the memory accessing of a program on the ARM processor. Basically, I want to get 'instruction_address : R/W : memory_address' by tracing the instruction execution flow.
For Intel processors, pintool can do this by instruction instrumentation, and the perf can also do this by sampling (simply use 'perf mem' command).
Is there any similar way to trace the memory accesses on an ARMv8 architecture (the ARM-Linux is running on it)?
You can just use perf for ARM.
Alternatively have a look at the strace tool in Linux. It traces system calls and signals (including: network, file activity, memory calls). It is not dependent on the processor type, but it needs advanced knowledge to interpret those messages.
For instructions how to use it, this is a good thread.
Related
I am using Linux 5.8.18 to do performance tuning, then I hit a confusion.
PMU in X86 is limited resource, and perf is the tool to use the PMU to complete profiling/sampling.
IIRC, perf document says the PMU resource is being shared by different processes, so Linux kernel will keep/snapshot the PMCs during process scheduling.
To verify that PMU setting is process specific, I did following tests.
A process running in background to call perf API to enable and use X86 FIXed_Counter0 (instruction retired) (MSR 0x309) on CPU0.
Then in the bash, I rdmsr -p0 0x309, I found the counter is increasing when the process is running in the background.
I had thought that each process (A and Bash) should have its own snapshot of the PMC (FIXed_Counter0 in this case), but the test shows that the PMC is global visible...
I got really confused.
both strace and ftrace seem to be used for tracing function calls in Linux. What's the difference?
strace is a utility which allows you to trace the system calls that an application makes. When an application makes a system call, it is basically asking the kernel to do something, eg file access. Use the command man strace to get strace documentation and man syscalls to get information on system calls.
ftrace is a tool used during kernel development and allows the developer to see what functions are being called within the kernel. The documentation is here and states:
Ftrace is an internal tracer designed to help out developers and
designers of systems to find what is going on inside the kernel.
It can be used for debugging or analyzing latencies and
performance issues that take place outside of user-space.
Is it possible to trace all the system calls/Interrupt generated by KVM to interact with hardware. I know there are tools like strace which can trace all the system calls generated by any C program but how to do the same if you want to get all the system calls for a hypervisor.
User space part (e.g. qemu) is a regular process, so strace will work for syscall tracing. Kernel-space part (KVM) may be traced via SystemTap or similar tool.
I am new to linux kernel.
wandering how to browse the complete flow, right from the power up of CPU.
Basic idea on BIOS/ROM code.
can I have some tool to debug the complete kernel ?
or
raw code browsing is preferable ?
The following tools may help you to debug Linux kernel
Dynamic Probes is one of the popular debugging tool for Linux which developed by IBM. This tool allows the placement of a “probe” at almost any place in the system, in both user and kernel space. The probe consists of some code (written in a specialized, stack-oriented language) that is executed when control hits the given point. Resources regarding dprobes / kprobes listed below
http://www-01.ibm.com/support/knowledgecenter/linuxonibm/liaax/dprobesltt.pdf
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.107.6212&rep=rep1&type=pdf
https://www.redhat.com/magazine/005mar05/features/kprobes/
https://sourceware.org/systemtap/kprobes/
http://www.ibm.com/developerworks/library/l-kprobes/index.html
https://doc.opensuse.org/documentation/html/openSUSE_121/opensuse-tuning/cha.tuning.kprobes.html
Linux Trace Toolkit is a kernel patch and a set of related utilities that allow the tracing of events in the kernel. The trace includes timing information and can create a reasonably complete picture of what happened over a given period of time. Resources of LTT, LTT Viewer and LTT Next Generation
http://elinux.org/Linux_Trace_Toolkit
http://www.linuxjournal.com/article/3829
http://multivax.blogspot.com/2010/11/introduction-to-linux-tracing-toolkit.html
MEMWATCH is an open source memory error detection tool. It works by defining MEMWATCH in gcc statement and by adding a header file to our code. Through this we can track memory leaks and memory corruptions. Resources regarding MEMWATCH
http://www.linuxjournal.com/article/6059
ftrace is a good tracing framework for Linux kernel. ftrace traces internal operations of the kernel. This tool included in the Linux kernel in 2.6.27. With its various tracer plugins, ftrace can be targeted at different static tracepoints, such as scheduling events, interrupts, memory-mapped I/O, CPU power state transitions, and operations related to file systems and virtualization. Also, dynamic tracking of kernel function calls is available, optionally restrictable to a subset of functions by using globs, and with the possibility to generate call graphs and provide stack usage. You can find a good tutorial of ftrace at https://events.linuxfoundation.org/slides/2010/linuxcon_japan/linuxcon_jp2010_rostedt.pdf
ltrace is a debugging utility in Linux, used to display the calls a user space application makes to shared libraries. This tool can be used to trace any dynamic library function call. It intercepts and records the dynamic library calls which are called by the executed process and the signals which are received by that process. It can also intercept and print the system calls executed by the program.
http://www.ellexus.com/getting-started-with-ltrace-how-does-it-do-that/?doing_wp_cron=1425295977.1327838897705078125000
http://developerblog.redhat.com/2014/07/10/ltrace-for-rhel-6-and-7/
KDB is the in-kernel debugger of the Linux kernel. KDB follows simplistic shell-style interface. We can use it to inspect memory, registers, process lists, dmesg, and even set breakpoints to stop in a certain location. Through KDB we can set breakpoints and execute some basic kernel run control (Although KDB is not source level debugger). Several handy resources regarding KDB
http://www.drdobbs.com/open-source/linux-kernel-debugging/184406318
http://elinux.org/KDB
http://dev.man-online.org/man1/kdb/
https://www.kernel.org/pub/linux/kernel/people/jwessel/kdb/usingKDB.html
KGDB is intended to be used as a source level debugger for the Linux kernel. It is used along with gdb to debug a Linux kernel. Two machines are required for using kgdb. One of these machines is a development machine and the other is the target machine. The kernel to be debugged runs on the target machine. The expectation is that gdb can be used to "break in" to the kernel to inspect memory, variables and look through call stack information similar to the way an application developer would use gdb to debug an application. It is possible to place breakpoints in kernel code and perform some limited execution stepping. Several handy resources regarding KGDB
http://landley.net/kdocs/Documentation/DocBook/xhtml-nochunks/kgdb.html
First, see related question Linux kernel live debugging, how it's done and what tools are used?. Try to use KDB or Ftrace.
If your intention is understanding whole flow of Linux kernel, running Linux kernel on QEMU can be easy way to learn how Linux works. Esp. you can emulate many CPU types without real H/W. or how about user mode Linux?
This document can be helpful to debug kernel on QEMU.
Just adding, the Linux kernel is not very suitable for debugging. Linus Torvalds once stated that he's againts supportng kernel debugging in Linux because it leads to badly written code.
I used kdbg, however I didn't find it very useful, what I suggest is to debug the kernel the oldschool way, using printk.
I would like to monitor the the context switching behavior in a multi-threaded pthread application.
In other RTOSes(Micro C OS) I have been able to register a context switch callback for each thread in the application, and then log (or toggle a gpio) and watch the thread context switching in real time. This was a valuable tool for debugging the real time behavior and interaction of the multiple threads.
My current environment is embedded linux utilizing the pthread api. Is there a way to monitor each of the context switches?
Not in the way you describe, however there are various profiling tools for Linux, like oprofile, SystemTap and perf events, I'm not sure how well they'd fit into embedded development though.
EDIT: perf is probably best (if you are running a recent enough kernel to use it) since it's in the mainline so you just have to turn it on, and it's really basic.
EDIT: if none of those work for you you can always modify the kernel context switch code...
EDIT: I missed one of the tracing frameworks, there is also LTTng
If you're using busybox and can compile your own kernel perf is probably the most minimal way to go, it's consists of turning on perf events in the kernel and compiling the perf tool that comes with the kernel source (it's in tools/perf)