Kprobes vs ftrace. Share Improve this answer Kprobes are the classic kprobes.

Kprobes vs ftrace txt from the kernel source for Ftrace makes a cache of pid mappings to comms to try to display comms for events. 9 mainline - 6. panchamukhi @ gmail. If you like BoxMatrix then please contribute Supportdata, Supportdata2, Firmware and/or Hardware (get in touch). The “notrace” list takes Using ftrace to hook to functions This function is used by perf and kprobes that gets the ip address from the user (usually using debug info from the kernel). > The requested ftracetest has been sent as an own patch set, since it > has no dependency to these patches. It's a probe somewhere in a kernel function, it can be at entry or any random instruction in it using the k:f+0x10 syntax; It doesn't have type info, all you get is argX which you have to cast to the appropriate type; kfuncs are the 'next gen' probes: they use btf for type info so types are known at compile time. Also an alternative function from a live patch is called with the help of a custom ftrace handler. debug. Here’s an example of a KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it eliminates the need for a trap, as well as the need to emulate or single-step instructions. Introduction; The ftrace context; The ftrace_ops structure; The callback function; Protect your callback; The ftrace - Function Tracer; Using ftrace to hook to functions; Fprobe - Function entry/exit probe; Kernel Probes (Kprobes) Kprobe-based Event Tracing; Uprobe-tracer: Uprobe-based Event Tracing; Fprobe-based Event Tracing; Using the Linux Kernel Tracepoints. kprobes on ftrace. Signed-off-by: Jianlin Lv <iecedge@gmail. Using Ftrace for Kernel Function Tracing Subject [PATCH ftrace/core v4 0/4] ftrace, kprobes: Introduce IPMODIFY flag for ftrace_ops to detect conflicts: From: Masami Hiramatsu <> Date: Mon, 28 Jul 2014 05:22:15 +0000 Date: Thu, 9 Jan 2025 18:39:33 -0800: From: Charlie Jenkins <> Subject: Re: [PATCH] Documentation: riscv: Remove KPROBES_ON_FTRACE Add DYNAMIC_FTRACE_WITH_REGS and KPROBES_ON_FTACE suppport with another ftrace implementation in parallel with mcount-based ftrace +. Kernel Probes (Kprobes)¶ Author. 289 mainline - 6. Linux kernel function calls (which functions in my TCP stack are being called?) 3. Slots are now exactly one instruction long. > > Kernel Probes (Kprobes)¶ Author:. 3 dynamic ftrace; Selecting function filters via index; Dynamic ftrace with the function graph tracer; ftrace_enabled; Filter commands; trace_pipe; trace entries; Snapshot; Instances; Stack trace; More; Using ftrace to hook to functions. It can be used to trace a wide range of kernel events, from function calls and system calls to interrupts and network packets. Tracepoints (see Using the Linux Kernel Tracepoints) can be used without creating custom kernel modules to register probe functions using the event tracing infrastructure. However, LKRG does cover a lot > >>> on ftrace" without using the current HAVE_KPROBES_ON_FTRACE infrastructure > >>> which is currently only used by x86. cn> wrote: > Patch 4/5 is from arm64’s KPROBES_ON_FTRACE, I think which is needed by > all RISC with both KPROBES_ON_FTRACE and -fpatchable-function-entry. The kernel code shows that if the current cpu is occupied by other KProbes events, there will be kporbes missing and increase the count of p->nmissed. , SystemTap [4]) now use the kprobes infrastructure as a base. Hi - In a few contexts, it comes up as to whether it is faster to probe process syscalls with kprobes or with something higher level such as [PATCH ftrace/core v6 2/5] ftrace, kprobes: Support IPMODIFY flag to find IP modify conflict From: Masami Hiramatsu Date: Thu Nov 20 2014 - 21:29:41 EST Next message: Masami Hiramatsu: "[PATCH ftrace/core v6 3/5] kprobes: Add IPMODIFY flag to kprobe_ftrace_ops" Previous message: Masami Hiramatsu: "[PATCH ftrace/core v6 1/5] kprobes/ftrace: Recover Hi, Here is the version 2 of the series of patches which introduces IPMODIFY flag for ftrace_ops to detect conflicts of ftrace users who can modify regs->ip in their handler. I've described some of them as hacks, which they are, as they use creative workarounds for the lack of some in-kernel features. ” - Support per-event and per-instance settings - Kprobes, synthetic events, actions and histogram are available The ftrace_ops flags are all defined and documented in include/linux/ftrace. kprobes on ftrace" KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it eliminates the need for a trap, as well as the need to emulate or single-step instructions. 3) Fixing of numerous problems in instruction In order for kprobes to be enabled we should set “CONFIG_KPROBES=y” while compiling the kernel. Fprobe is a function entry/exit probe mechanism based on ftrace. In the typical case, Kprobes-based instrumentation is packaged as A few different kinds of things you might want to trace: 1. Why? Because by default, BCC extracts the kernel header to /tmp. 12. We compare the results captured by bcc tools with the packets captured by tcpdump and found that KProbes will lose some events and cause defects in our developed programs. It's built into the kernel, and can consume tracepoints, kprobes, and uprobes, and provides a few capabilities: event If you want to see the frequency of do_filp_open() calls or the parameters passed to do_filp_open() during its execution, you will need to use kprobes. kprobes, stack tracing, profiling, etc). Function flow tracing: ftrace function graphing. ]event On Mon, Nov 07, 2022 at 03:35:07PM +0000, Will Deacon wrote: > On Mon, Nov 07, 2022 at 03:32:24PM +0000, Mark Rutland wrote: > > On Mon, Nov 07, 2022 at 02:49:31PM +0000, Will Deacon wrote: > > > [+Mark R] > > > On Thu, Jul 28, 2022 at 02:02:50AM +0000, Jianlin Lv wrote: > > > > This is the arm64 version of ftrace-based kprobes to avoid the overhead > > > > This allows the user to add tracing events (similar to tracepoints) on the fly via the ftrace interface. kprobes on ftrace 对于这个冗长的post道歉，我很难用更短的方式来制定它。 此外，也许这是更适合Unix和Linux堆栈交换，但我会先在这里尝试，因为有一个ftrace标记。. 233 mainline - 5. Using ftrace to hook to functions This function is used by perf and kprobes that gets the ip address from the user (usually using debug info from the kernel). This option is available only for the event which group name is “kprobes”. conf. ~ # mount -t debugfs debugfs /sys/kernel/debug/ Boot-time tracing allows users to trace boot-time process including device initialization with full features of ftrace including per-event filter and actions, histograms, kprobe-events and synthetic-events, and trace instances. Also an alternative function from a live patch is called • ftrace-based kprobe adds new ftrace_ops for handling ftrace mcount handler. it can be bypassed without too much effort if malware is aware of it. All we’re going to use it for is to do the job of kallsyms_lookup_name() to lookup itself!. Most of these problems are solved by using the dynamic ftrace framework as a base. arch supports compiler driven stack overflow protection. Hardware LKDDb. Jim Keniston <jkenisto @ us. kprobes on ftrace From: Masami Hiramatsu Date: Tue Oct 21 2014 - 05:37:50 EST Next message: Jingchang Lu: "[PATCH] serial: of-serial: fix uninitialized kmalloc variable" Previous message: Johan Hovold: "Re: [PATCH v2 01/47] kernel: Add support for poweroff handler call chain" In reply to: Heiko Carstens: "Re: [PATCH 0/2] s390 vs. I love Ftrace, it's a kernel hacker's best friend. There are lots of terminology around tracing such as ftrace, kprobe, uprobe, tracing event. A return probe fires when a specified function returns. 124 mainline - 5. Userspace function calls (did mallocget called?) 4. Use the command man strace to get strace documentation and man syscalls to get information on system calls. A kprobe can be inserted on virtually any instruction in the kernel. My metamonk@yahoo. Please use hippie2000@webnmail. 15. kretprobes. arch supports combined kprobes and ftrace live patching. > > > > > Ditto, skip two nop instructions should > > instruction_pointer_set(regs, dynamic ftrace; Selecting function filters via index; Dynamic ftrace with the function graph tracer; ftrace_enabled; Filter commands; trace_pipe; trace entries; Snapshot; Instances; Stack trace; More; Using ftrace to hook to functions. Kprobes enables you to dynamically break into any kernel routine and collect debugging and performance information non-disruptively. com> flag to register_kprobe, and then kprobes sets FTRACE_OPS_FL_IPMODIFY when registering with ftrace for that probe. [instance. Kprobes allows you to dynamically attach probe functions to any Since kprobes trace arbitrary functions, tools relying on them may easily break from one Linux version to the next. So kprobes and ftrace work with and without patch 2/2, all I want to achieve is that the overhead of the mcount block gets reduced to a single 3. stackprotector. 三、Kprobes. In this version, I fixed some bugs in previous version and added a patch which made kprobe itself free from IPMODIFY except for jprobe. HAVE_KRETPROBES. static void notrace ftrace_callback(unsigned long ip, unsigned long parent_ip, struct ftrace_ops *ops, struct pt_regs *regs) { regs->ip = (unsigned long) hook_function; } This will make the hook function to execute instead of the hooked function. kprobe allows us Boot-time tracing allows users to trace boot-time process including device initialization with full features of ftrace including per-event filter and actions, histograms, kprobe-events and A Kprobe is registered as a ftrace handler when the function entry is probed, see CONFIG_KPROBES_ON_FTRACE. 71 mainline - 6. Jprobes allow to call your function with the same signature as the probed one on entry to the latter. g. If you register a kprobe, the pre_handler gets executed before the actual function and post_handler after the actual function (although Ftrace might be even better). Theodore Ts’o. ftrace. > >> I'm not sure about s390 nor have the machine, so it is very helpful if you Re: [PATCH 0/2] s390 vs. e. It cannot be disabled if there is a callback with FTRACE_OPS_FL_PERMANENT set registered. com is not reachable by me since years. Additionally, kprobes has been extensively used for kernel tracing [9], performance evaluation, fault-injection, etc. Other presentations: BPF: Tracing and More, by Brendan Gregg at linux. Instead of using ftrace full feature, if you only want to attach callbacks on function entry and exit, similar to the kprobes and kretprobes, you can use fprobe. alibaba. Custom eBPF programs execute when these kprobes are hit, which record timestamps on the issue of I/O, fetch them on completion, calculate the delta time, and then store this in a log 2 histogram. Kprobes allows you to trap at almost any kernel address and execute a callback function. TODO. ftrace is a tool used during kernel development Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company dynamic ftrace; Selecting function filters via index; Dynamic ftrace with the function graph tracer; ftrace_enabled; Filter commands; trace_pipe; trace entries; Snapshot; Instances; Stack trace; More; Using ftrace to hook to functions. The "notrace" list takes precedence over On Fri, 26 Mar 2021 22:12:18 +0800 Huang Pei <huangpei@loongson. uprobes Implementation based on inodes Must be enabled with CONFIG_UPROBES Uprobes described as: inode (file), offset in file (map), list of associated actions, arch specific info (for instruction handling) Probes stored in an rb_tree Register a uprobe: add probe to probe tree (if needed), and insert the arch specific BP instruction Handle the uprobe by calling the actions These events are similar to tracepoint-based events. After a bit of back-and Hi Filipe, first, thanks for the test. Please disable this with care. 13-rc6 [click here for custom version] architecture: x86 arm arm64 powerpc mips sparc ia64 arc riscv nds32 m68k microblaze alpha unicore32 parisc blackfin These events are similar to tracepoint-based events. But there are some limitations, see below. Raw data from LKDDb: (none) Sources. If in doubt, say "N". 18-rc1" Previous message: bpqw: "[PATCH 1/1 v3] driver:mtd:spi-nor: Add Micron quad I/O support" In reply to: Heiko Carstens: "Re: [PATCH 0/2] s390 vs. Linux 4. The following steps will illustrate how to assign the handlers and build the module. Updated:. Kprobes use the breakpoint mechanism to dynamically instrument Linux kernel code. Masami Hiramatsu <mhiramat @ redhat. If a glob is used to set the filter, functions can be added to a "notrace" list that will prevent those functions from calling the callback. Uprobe tracer will access memory by given type. 4. While i have read that kprobes are susceptible to time-of-check-to-time-of-use attacks, i would like to know it the same holds up for fentry/ fexit probes also known as BPF-trampoline. au 2017 (slideshare, youtube, PDF). This can be Kprobes are the classic kprobes. At first, we thought that hooking functions with the Linux Security API This uses kernel dynamic tracing (kprobes) to instrument functions for the issue and completion of block device I/O. In Linux, we have: ftrace; kprobe; uprobe; perf_event; tracepoints; eBPF; For all these tools, we can think this way: Tracing needs two parts, 1) Mechanims to get data and do callback. Not all tracepoints can be traced using the event tracing system; the kernel developer must provide code snippets 3. org> Subject: [PATCH v6 tip 0/8] tracing: attach eBPF programs to kprobes The ftrace infrastructure was originally created to attach callbacks to the beginning of functions in order to record and trace the flow of the kernel. Introduction¶. There are several tools which leverage kprobes like SystemTap, perf and ftrace. Introduction; The ftrace context; The ftrace_ops structure; The callback function; Protect your callback; The Linux Kernel: Re: [PATCH 0/2] s390 vs. The Kprobe system lets you dynamically insert breakpoints into a running kernel. pt@hitachi. There are currently two types of probes: kprobes, and kretprobes (also called return probes). g, tcp_*): ftrace, because it's fast to initialize. 探测手段：3种，kprobe、jprobe和kretprobe。 使用方式：2种，第一种是编写内核模块，向内核注册探测点，自定义回调函数；第二种是使用kprobes in ftrace，这种方式结合kprobe和ftrace，可以通过kprobe来优化ftrace跟踪函数。 > introduce a new helper function check_ftrace_location(). 4. These events are similar to tracepoint based events. com> This patch allow kprobes on ftrace call sites. Approach 1: Jprobes. This page is automaticly generated with free (libre, open) software lkddb(see lkddb-sources). If possible, I'd like to Re: [PATCH 0/2] s390 vs. Li Zefan and Tom Zanussi. > > v1: > We would like to implement an architecture specific variant of "kprobes > on ftrace" without using the current HAVE_KPROBES_ON_FTRACE infrastructure > which is Using ftrace to hook to functions This function is used by perf and kprobes that gets the ip address from the user (usually using debug info from the kernel). kprobes on Hi Masami, thank you for your comments! On Thu, Oct 16, 2014 at 02:49:56PM +0900, Masami Hiramatsu wrote: > (2014/10/16 0:46), Heiko Carstens wrote: > > we would like to implement an architecture specific variant of "kprobes > > on ftrace" without using the current HAVE_KPROBES_ON_FTRACE infrastructure > > which is currently only used by x86. This function is used by perf and kprobes that gets the ip address from the user (usually using debug info from the kernel). Introduction; The ftrace context; The ftrace_ops structure; The callback function; Protect your callback; The Kernel Probes (Kprobes)¶ Author:. de instead. arch supports kernel function-return probes. , the difference between a pre_handler and a post_handler, and how to use the maxactive and nmissed fields of a kretprobe. Frequency counting many functions (e. At least on x86, the implementation of Kprobes relies on the fact that preemption is disabled while the Kprobe handlers run. 176 mainline - 5. Perhaps, you can use Kprobes (Jprobes, to be exact), for that purpose. Re: [PATCH 0/2] s390 vs. ftrace - Function Tracer describes how to enable events on a per-thread basis using set_ftrace_pid. It's built into the kernel, and can consume tracepoints, kprobes, and uprobes, and provides a few capabilities: event tracing, with optional filters and arguments; event counting and timing, summarized in-kernel; and function-flow walking. Don't drink and probe. This is to ensure that BCC always picks up the latest kernel headers. From: Janet Liu <janet. The kernel provides tracepoint data on all pm device callbacks, and the tool adds kprobes on other functions of interest in the The kprobes mechanism makes use of software breakpoint and single stepping support available in the ARM v8 kernel. Introduction; The ftrace context; The ftrace_ops structure; The callback function; Protect your callback; The Are tracepoints redundant in Linux kernel after kprobes support for ftrace? 2 kprobe handler not getting triggered for specific function. Here are the BPF front-ends config_have_kprobes_on_ftrace - kernelversion: stable - 6. 6. The “notrace” list takes And also we can keep the ftrace and kprobes backends quite separated. ibm. This patch implements KPROBES_ON_FTRACE for arm64. Linux tracing systems. Probably the most easy one: if Jprobes are suitable for your task, you could give them a try. Linuxカーネルの起動処理は、様々なことが行われるのにそれをデバッグする方法はprintkだったり、逆にkgdbを外部デバッガから繋いだりと、結構な手間がかかっていました。カーネルが起動してしまえば、ftraceにperf, BPF, systemtapと複数の手段が使えるのに、起動時の [PATCH] Documentation: riscv: Remove KPROBES_ON_FTRACE: Date: Wed, 8 Jan 2025 10:03:42 +0800: From: Chen Pei <cp0613@linux. The big distinction between fexit and kretprobe programs is that fexit one has access to both input If function tracer is enabled and the arch supports full passing of pt_regs to function tracing, then kprobes can optimize on top of function tracing. The data is retrived from: Linux kernel From:: Alexei Starovoitov <ast@plumgrid. When an application makes a system call, it is basically asking the kernel to do something, eg file access. And the issue is not specific to btrfs_sync_file function but to other, independent functions as well. See Those events can be inserted wherever kprobes can probe, and record various register and memory values. 1. Some of the flags are used for internal infrastructure of ftrace, but the ones that users should be aware of are the following: This function is used by perf and kprobes that gets the ip address from the user (usually using debug info from the kernel). > introduce a new helper function check_ftrace_location(). ok. Changes since v2 include: 1) Removal of NOP padding in kprobe XOL slots. h. Prasanna S Panchamukhi <prasanna. In this example, better usability is shown with the ability to directly dereference pointer arguments, like in normal C, instead of using various read helpers. strace is a utility which allows you to trace the system calls that an application makes. In order to make this work a small common code change is necessary which removes a check if kprobe is being placed on an ftrace location (see first patch). You can use it to weed out performance bottlenecks, log specific events, trace problems Kprobes, of course, has no way to distinguish the deliberately injected faults from the accidental ones. System calls 2. ko version Also on TODO list: – perf interface: exploit symbol table, debuginfo – uprobes booster: eliminate the single-step trap syscall tracing overheads: utrace vs. 3. You can define new events and trace it via ftrace or any other tracing tools. If a pid for a comm is not listed, then “<>” is displayed in the output. ]event KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it eliminates the need for a trap, as well as the need to emulate or single-step instructions. Kprobes Optimized Kprobes int3 Relative jump Die notifier Kprobes Single step Direct execution Jump in Jump back Emulate int3/Handler call Die notifier Post Kprobes Optimize Re: [PATCH 0/2] s390 vs. So, with patch 2/2 the ftrace location of a function now matches the first instruction of a function and the check within kprobes. Is this something that could still be supported? In cases like perf Ftrace: A built-in tracing framework in the Linux kernel, which utilizes tracepoints and kprobes for function tracing and provides various tracing options. Compared with kprobes and kretprobes, fprobe gives faster instrumentation for multiple functions with single handler. arm64 makes use of GCC -fpatchable-function-entry=2 option to insert two nops. Ftrace was added to the Linux kernel back in 2008, but a lot of people still don’t quite get what it is, or what it can empower them to do. ) uprobe is an experimental tool, and only works on From:: Masami Hiramatsu <masami. Purpose of tracepoints; Usage; Event Tracing; Subsystem Trace Points: kmem; Subsystem Bug is fatal, because it makes the kprobes directory dissapear from the ftrace debug directory; Just creating the kprobe would not make it appear in the ftrace log - it also needs to be enabled; the necessary code for enabling is there - but Overview¶. A number of new features have been added: support for colocated probes ftrace/kprobes can allow messing with a lot of kernel code to gather sensitive information or hook parts of the code (like LKRG does). When the function is traced, the first nop will be modified struct kprobe {//helin struct hlist_node hlist; /* list of kprobes for multi-handler support */ struct list_head list; //helin: 支持多个probe handlers /*count the number of times this probe was temporarily disarmed */ unsigned long nmissed; //helin: ++ breakpoint : addr/symbol + offset /* location of the probe point */ kprobe_opcode_t * addr; //helin /* Allow user to indicate symbol I am reading up upon attaching eBPF programs in the kernel in a security context. Eigler 2009-04-28 17:01:17 UTC. HAVE_OPTPROBES. BCC only updates the cached 11 perf & perf_events perf_events is the kernel infrastructure, perf is the userspace tool Lives in tree at tools/perf The primary developers are Ingo Molnar and Peter Zijlstra Supports CPU performance counters, software events, tracepoints, kprobes and uprobes Manpages are provided, see man -k perf Require kernel built with appropriate configuration options for The private bpftrace repository has just been made public, which is big news for DTrace fans. x Tracing Tools: Using BPF Superpowers, by Brendan Gregg at These events are similar to tracepoint based events. But callbacks to the start of a function can have other use cases. com> To:: Steven Rostedt <rostedt@goodmis. 10. Unlike the tracepoint-based event, this can be added and removed dynamically, on the fly. com> Since commit 7caa9765465f60 ("ftrace: riscv: move from REGS to ARGS"), kprobe on Important differences, compared to kprobes, are improved performance and usability. > > But since V7, no further patches are released, what protocol should I follow if > I need these two patches? > If you need this patch, ftrace and perf-tools. Created by Alastair Robertson, bpftrace is an open source high-level tracing front-end that lets you analyze systems in custom However, ftrace's tracepoint always work. Kprobes traces its roots back to DProbes (discussed later). For instance, the name of the function or one of its These events are similar to tracepoint-based events. When you place an ordinary (not Ftrace-based) Kprobe on an instruction, the first byte of that instruction is blktraceというツールによって使われますが、ftrace単体でもトレース内容を見ることは可能です。（統計処理などはツールが必要） Enable kprobes-based dynamic events (CONFIG_KPROBE_EVENT) kprobesを使った動的イベント機能を追加します。 While I was working on refining this technique, @f0lg0 opened an issue on GitHub bringing up exactly this problem, and proposed a cool technique that used kprobes instead. 无论如何 – 我想观察一个用户程序的机器指令执行在一个完整的function_graph捕获使用ftrace的上下文。一个问题是，我需要这个旧的内核： Hi Masami, thank you for your comments! On Thu, Oct 16, 2014 at 02:49:56PM +0900, Masami Hiramatsu wrote: > (2014/10/16 0:46), Heiko Carstens wrote: > > we would like to implement an architecture specific variant of "kprobes > > on ftrace" without using the current HAVE_KPROBES_ON_FTRACE infrastructure > > which is currently only used by x86. kprobes on ftrace From: Masami Hiramatsu Date: Sun Oct 19 2014 - 21:32:11 EST Next message: Linus Torvalds: "Linux 3. Introduction; The ftrace context; The ftrace_ops structure; The callback function; Protect your callback; The - Kernel command line + boot-time tracing in ftrace - Configured via bootconfig - Dedicated top-level key “ftrace. • In this case, ftrace starts checking which ftrace_ops should be invoked from ip address • Each ftrace hit causes 2 other hashtable checks! – Mcount->ftrace->hash check->kprobe->hash check Pointer Pointer Pointer entry entry Ftrace filter Hash Pointer 1. So it can probe wherever kprobes can probe (this means, all functions except those with __kprobes/nokprobe_inline annotation and those marked NOKPROBE_SYMBOL). Ftrace is a built-in tracing tool that comes with the Linux kernel. (uprobe the user-level counterpart of my kprobe tool, which traces kernel functions. optprobes. Kprobes makes no attempt to prevent probe handlers from stepping on each other -- e. > > v1: > We would like to implement an architecture specific variant of "kprobes > on ftrace" without using the current HAVE_KPROBES_ON_FTRACE infrastructure > which is Kernel Probes (Kprobes) Kprobe-based Event Tracing; Uprobe-tracer: Uprobe-based Event Tracing; Fprobe-based Event Tracing; Using the Linux Kernel Tracepoints; If you want more explanation of a feature in terms of common code, review the common ftrace - Function Tracer file. Kprobes is useful for kernel debugging, non-intrusive instrumentation and testing. A Kprobe is registered as a ftrace handler when the function entry is probed, see CONFIG_KPROBES_ON_FTRACE. Two types exist: kprobes can be attached to all but a few blacklisted instruction ranges in a running kernel, while kretprobes are attached to a function and run when it returns. (2014/10/16 19:57), Heiko Carstens wrote: > Hi Masami, > > thank you for your comments! > > On Thu, Oct 16, 2014 at 02:49:56PM +0900, Masami Hiramatsu wrote: >> (2014/10/16 0:46), Heiko Carstens wrote: >>> we would like to implement an architecture specific variant of "kprobes >>> on ftrace" without using the Kprobes Jump Optimization (x86) Kprobes enhancement feature by replacing a breakpoint with a jump instruction. kprobes can also use a jump optimization, not just at the There are at least two approaches. Both kprobes and kretprobes allows you to put probe on a particular instruction in the kernel address. Prefix ‘s’ and ‘u’ means those types are signed and unsigned respectively. Custom “events” that you’ve defined either in userspace or in the kernel All of these things are possible, but it t Linux tracing system is confused as there are many faces of tracing. This instrumentation can be packaged as a kernel module (using the register_probe uprobe is a tool I wrote for the perf-tools collection, to explore uprobes via Linux ftrace – the built-in tracer. 2) Disabling of interrupts during execution in single-step mode. kprobes on On the kernel side, kprobes is the mechanism that allows tracing any function call inside the kernel. So all of the above is a long-winded way of establishing that we need something else other than kprobes in kernel tracing. They are the close relatives of kprobes (see their detailed description and links to the examples in the kernel docs). ftrace is not programmable by normal users, it only prints the info. . 0 why does kgdb not show function symbols when debugging vmlinux? 2 Debugging kernel with /proc/kcore. ftrace-based kprobe cannot work if disable the ftrace. INSTANCE. If a glob is used to set the filter, functions can be added to a “notrace” list that will prevent those functions from calling the callback. Several tools (e. com> Concepts: Kprobes and Return Probes¶. HAVE_STACKPROTECTOR. The ftrace log is the primary source of information. kprobes Frank Ch. v3: Changed patch 1/2 to incorporate feedback from Steven Rostedt and Masami Hiramatsu: rename helper function check_ftrace_location() to arch_check_ftrace_location() and convert it to a weak function, so architectures can override it without the need for new config option. com> Subject: [PATCH ftrace/core v4 0/4] ftrace, kprobes: Introduce IPMODIFY flag for ftrace_ops to detect conflicts CONFIG_HAVE_KPROBES_ON_FTRACE - Architecture supports combined kprobes and ftrace live patching - BoxMatrix FRITZ!Box Research Wiki. Masami Hiramatsu <mhiramat @ kernel. Boot Events Tracking time for key boot events/functions – Kernel log – ftrace Identify critical events/functions to trace – All initcalls Using the kprobes tool; Splicing; Using the ftrace utility; Below, we talk in detail about each of these kernel options. BPF kprobe attaching will become faster with multi-attach perf_event_open() once it is developed. ## Kprobes とは Kprobes は実行中のカーネルに処理を差し込むための仕組み。 kprobe_events は、カーネルモジュールを作成せずに kprobe を利用できる仕組み。Ftrace と同じインタフェースで probe を動的に作成できる。 The functions listed in these files can also be set on the kernel command line. To put it very simply: ftrace is a Linux kernel feature that lets you trace mentation purposes. The options ftrace_notrace and ftrace_filter will preset these files by listing a comma delimited set of functions. org>, Josh Poimboeuf <jpoimboe@redhat. kprobes on ftrace" kprobe是一个轻量级的内核调试工具，也是其他更高级的内核调试（如perf和systemtap的基础）。Kprobes 提供了一个强行进入任何内核例程并从中断处理器无干扰地收集信息的接口，使用 Kprobes 可以收集处理器寄存器和全局数据结构等调试信息。 开发者甚至可以使用 Kprobes 来修改 寄存器值和全局数据结构 Event Tracing¶ Author:. Types¶. See ftrace. Kretprobes meddle with the return address of the function on the stack to KProbes is a debugging mechanism for the Linux kernel which can also be used for monitoring events inside a production system. This way you can trace system calls, but also what happens inside system > >>> on ftrace" without using the current HAVE_KPROBES_ON_FTRACE infrastructure > >>> which is currently only used by x86. 5 Local Event Enablement with PCL¶ Events can be activated and tracked for the duration of a process on a local basis using PCL such as follows. If you want to use perf tools, this option is strongly Linux Kernel: [PATCH v3 0/2] s390 vs. Several types are supported for fetch-args. Kprobes has evolved from its first appearance. See the following urls: https://lwn Overview¶. register_kprobe() establishes a probepoint and specifies the callback. Share Improve this answer Kprobes are the classic kprobes. Introduction; The ftrace context; The ftrace_ops structure; The callback function; Protect your callback; The • ftrace-based kprobe adds new ftrace_ops for handling ftrace mcount handler. Note that it's not impossible, but in such cases we'd need to figure out the offset in the function body where inline code begins (kprobes can be placed on most instructions, not just function entry). The “notrace” list takes kprobes provide "pre" handlers that run before the specific instruction, and "post" handlers that run afterwards. All the tools I used here are from my perf-tools collection, which are front-ends to ftrace and related tracers (kprobes, tracepoints, and the function profiler). - If KPROBE_FLAG_IPMODIFY is not used, kprobe_ftrace_handler() can detect when a kprobe handler changes regs->ip and restore it to its original value (regs->ip = ip). This is the arm64 version of ftrace-based kprobes to avoid the overhead with regular kprobes, by using the ftrace infrastructure. This option is also required by perf-probe subcommand of perf tools. Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Visit the blog Boot-time tracing allows users to trace boot-time process including device initialization with full features of ftrace including per-event filter and actions, histograms, kprobe-events and synthetic-events, and trace instances. c which prevents putting a kprobe on an ftrace location triggers. Using the Linux Security API. com> To:: Ingo Molnar <mingo@kernel. This means we have a virtual big NOP instruction there. arch supports live patched optprobes. liu@unisoc. kprobes on Linux Kernel: Re: [PATCH 0/2] s390 vs. Tested on berlin arm64 platform. 3 Intro¶. > > > So basically, kprobes on ftrace will skips 2 NOP instructions (the compiler installed > > > 2 nops) and call post handler. #カーネル起動時トレース. It's a probe somewhere in a kernel function, it can be at entry or any random instruction in it using the k:f+0x10 syntax; It doesn't have type info, all you get is argX which you have to cast to the appropriate type; kfuncs are the 'next gen' probes: Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company They explain certain things that you’ll need to know in order to make the best use of Kprobes -- e. Disabling it would be deterministic attack surface reduction whereas LKRG is a probabilistic protection, i. In fact, the first version of kprobes was a patch created by just taking the minimal, kernel-only portions of the DProbes framework. As far as i understand fentry/ fexit probes have lower overhead and do not trap to the eBPF program but After giving another talk on ftrace, the official tracer of the Linux kernel, I thought it might be useful to offer a quick primer for those that are still unfamiliar with it. hiramatsu. 1 Kprobes Kprobes [2] is perhaps the most widely accepted of all dynamic instrumentation mechanisms currently avail-able for the Linux kernel. The previous examples used kprobes, and these will need updating as the kernel changes. So it can probe wherever kprobes can probe (this means, all In all, ftrace, kprobe, uprobe, perf_event, tracepoints all have mechanisms to get data and do callback. Generally, these are useful in resolving kernel-panics. Slimmed down for LKML reviews: – x86 only – 1 uprobe per probepoint – limited number of uprobes per process – no function-return probes – no option to single-step inline – built-in only: no uprobes. ” in the bootconfig - Some existing ftrace kernel cmdline options are started with “kernel. > > Overview¶. com> Author:. This means we need a way to let our tracing/profiling code got invoked on a running system. , probing printk() and then calling printk() from a probe handler. This optimization avoids use of a trap with regular kprobes. Permalink. Ideally, everyone who wishes to retain performance while supporting Using ftrace to hook to functions This function is used by perf and kprobes that gets the ip address from the user (usually using debug info from the kernel). ‘x’ prefix implies it is unsigned. 1. Note however there is an ftrace optimization; when we place the kprobe at an ftrace site - function entry - the ftrace trampoline is used instead for kprobe handling. Instead of tracepoints, this is based on kprobes (kprobe and kretprobe). Depend on GCC with -fpatchable-function-entry. org> Concepts: Kprobes and Return Probes¶. ftrace Ftrace is a framework for tracing and profiling Linux kernel with the following features: Kernel functions tracing Call graph tracing Tracepoints support Dynamic tracing via kprobes Statistics for kernel functions Statistics for kernel events Essentially, ftrace built around smart lockless ring buffer implementation (see Documentation And I get this xxxxxxxxxxx k ip_rcv+0x0 [FTRACE], it means that the this kprobe is ftrace-based. com> Author. • In this case, ftrace starts checking which ftrace_ops should be invoked from ip address • Each ftrace hit causes 2 other hashtable checks! – Mcount->ftrace->hash check->kprobe->hash check Pointer Pointer Pointer entry entry Ftrace filter Hash Pointer Static events are boring 4 # cd /sys/kernel/tracing # echo 1 > events/sched/enable # cat trace # tracer: nop # # _-----=> irqs-off dynamic ftrace; Selecting function filters via index; Dynamic ftrace with the function graph tracer; ftrace_enabled; Filter commands; trace_pipe; trace entries; Snapshot; Instances; Stack trace; More; Using ftrace to hook to functions. dynamic ftrace; Selecting function filters via index; Dynamic ftrace with the function graph tracer; ftrace_enabled; Filter commands; trace_pipe; trace entries; Snapshot; Instances; Stack trace; More; Using ftrace to hook to functions. Additionally bcc's funccount utility also doesn't produce outputs. It is good. Instead of Tracepoint, this is based on kprobes (kprobe and kretprobe). I just suggest a lot of clean up ;-) On Sat 2025-01-11 15:42:27, Filipe Xavier wrote: > This new test makes sure that ftrace can trace a 2010 Uprobes, cont. xgg lnoopgeo swycpy zdoqv yqq jtqaf hswqtq nwzju ddcgm vspl