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Linux port of DTrace

Dec 2015 Paul D. Fox [email protected] http://www.twitter.com/crispeditor http://www.crispeditor.co.uk

Blog - latest news and stuff about the dtrace project:

http://crtags.blogspot.com/ http://www.crispeditor.co.uk/blog/

Download dtrace tarballs for linux here:

https://github.com/dtrace4linux/linux ftp://crispeditor.co.uk/pub/release/website/dtrace

Introduction

This is a port of the Sun DTrace user and kernel code to Linux. No linux kernel code is touched in this build, but what is produced is a dynamically loadable kernel module. This avoids licensing issues and allows people to load and update dtrace as they desire.

The goal of this project is to make available DTrace for the Linux platforms. By making it available for everyone, they can use it to optimise their systems and tools, and in return, I get to benefit from their work.

PayPal

If you want to make a donation for this software, feel free to do so. Nothing is asked of you - it is genuinely free software, but it can help guage interest and appreciation if you do.

You can pay by visiting the link below and clicking on "Donate", or use this reference for donations:

• [email protected]
• Paypal

Licensing

The original DTrace is licensed under Sun's (now Oracle) CDDL license. Original copyrights are left intact. No GPL code is incorporated into the release, to avoid legal conflicts.

Any mistakes or omissions in copyright attribution will be my mistake, so please let me know if there are such cases.

The linux kernel was referred to in order to engineer the glue for dtrace behavior, and there is no intention of making this code fall under anything other than CDDL. (If Oracle migrate to a GPL friendly license, then this port of dtrace can follow). I do not own the license or assert any rights on the licensing other than that expected of me as a consumer/supplier.

I have no political affiliation or preference for a licensing scheme, simply that Sun/Oracle has gracefully donated to the community a large body of work.

I reserve the right to change the licensing model for my own code at a later date, when and if someone puts forward a case as to the correct license agreement.

If the code is useful to you - great. Spread it around and get people to use, debug and enhance it.

GIT Repository

https://github.com/dtrace4linux/linux

(Theres an older and orphaned github repository under Peter McCormicks name, please ignore this as it has not been updated in a long while and is no longer active).

Installation

You may need to grab some extra packages for building DTrace. Use either of the following to download extra packages. This list may be incomplete depending on the version of your kernel/distro.

$ tools/get-deps-arch.sh	# if using ArchLinux
$ tools/get-deps.pl 		# if using Ubuntu
$ tools/get-deps-fedora.sh	# RedHat/Fedora

$ make all
$ make install
$ make load           (need to be root or have sudo access)

If the libdwarf package installed on the system is too old it still compiles without any problem, but you will get runtime errors from the io.d and/or sched.d files due to undefined kernel structure definitions.

If you get a undefined struct definition such as dtrace_cpu_t when running, please upgrade it.

Tested successfully with version 20100214 (whereas 20080409 is to old).

More details

Building is done in a build/ directory. The makefiles allow you to compile for alternate kernel releases in the same tree, which is useful for cross-version checking.

The result is:

build/dtrace               User land executable
build/drti.o               Object file for USDT apps
build/driver/dtracedrv.ko  Kernel loadable module

Installing will copy them to Solaris compliant locations:

/usr/sbin/dtrace
/usr/lib/dtrace/64/drti.o

You dont need to 'install' to run dtrace, but you will need to load the driver.

Kernel versioning

dtrace relies on a kernel module and so a binary is needed per system you deploy to, or kernel version.

dtrace is sensitive to the kernel - and attempts to cater for that, but very old, or very new kernels may not have been validated. Please feed back if that is the case.

A kernel strack trace is expected when loading the module, due to currently unknown reasons (the current theory is that the kernel ftrace mechanism which probes dtrace as its loaded gets confused by what it sees).

If you get a stack trace something like this in the logs when loading the module, this can safely be ignore (it appears to be no harm (unless you use system-tap and dtrace at the same time, then there could be a conflict):

[  182.556392] dtracedrv: module license 'CDDL' taints kernel.
[  182.556396] Disabling lock debugging due to kernel taint
[  184.760136] CPU: 5 PID: 11008 Comm: dtrace Tainted: P           O 3.12.0+scst+tf.1 #5
[  184.760140] Hardware name: To be filled by O.E.M. To be filled by O.E.M./SABERTOOTH 990FX, BIOS 0901 11/24/2011
[  184.760142]  ffffffffa093c8a0 ffffffff813c18b9 ffff8800dacdaa80 ffffffffa08f28ed
[  184.760146]  755f6f745f646162 ffff8800dacdaa80 ffff88040acbbb9c 0000000000000020
[  184.760149]  0000000000000001 ffffffffa09370c0 ffff8800dd020a80 ffffffffa08e7f3e
[  184.760151] Call Trace:
[  184.760156]  [<ffffffff813c18b9>] ? dump_stack+0x41/0x58
[  184.760165]  [<ffffffffa08f28ed>] ? mutex_enter_common+0x2d/0xeb [dtracedrv]
[  184.760172]  [<ffffffffa08e7f3e>] ? par_alloc+0x20/0xd0 [dtracedrv]
[  184.760178]  [<ffffffffa08f0894>] ? instr_provide_module+0x31/0x1f5 [dtracedrv]
[  184.760184]  [<ffffffffa08f489c>] ? sdt_open+0x3/0x3 [dtracedrv]
[  184.760189]  [<ffffffffa08f2980>] ? mutex_enter_common+0xc0/0xeb [dtracedrv]
[  184.760195]  [<ffffffffa08d83d0>] ? dtrace_probe_provide+0xcd/0xf7 [dtracedrv]
[  184.760201]  [<ffffffffa08d844f>] ? dtrace_open+0x55/0x10f [dtracedrv]
[  184.760203]  [<ffffffff812b3e60>] ? kobj_lookup+0xfc/0x133
[  184.760209]  [<ffffffffa08e7400>] ? dtracedrv_open+0x4c/0x51 [dtracedrv]
[  184.760212]  [<ffffffff812a3973>] ? misc_open+0x107/0x168
[  184.760216]  [<ffffffff8112c091>] ? chrdev_open+0x129/0x148
[  184.760218]  [<ffffffff8112bf68>] ? cdev_put+0x1a/0x1a
[  184.760220]  [<ffffffff81127082>] ? do_dentry_open+0x16c/0x22b
[  184.760221]  [<ffffffff8112720f>] ? finish_open+0x2c/0x35
[  184.760224]  [<ffffffff81134d9d>] ? do_last+0x9fd/0xc4a
[  184.760226]  [<ffffffff81135249>] ? path_openat+0x25f/0x5bd
[  184.760228]  [<ffffffff81141561>] ? mntput_no_expire+0x1b/0x16c
[  184.760230]  [<ffffffff811356a2>] ? do_filp_open+0x2d/0x75
[  184.760233]  [<ffffffff8111e32c>] ? kmem_cache_alloc+0x114/0x194
[  184.760235]  [<ffffffff813c4d93>] ? _raw_spin_unlock+0x9/0xb
[  184.760237]  [<ffffffff8113fa09>] ? __alloc_fd+0xfa/0x10c
[  184.760239]  [<ffffffff81126cfa>] ? do_sys_open+0x146/0x1d6
[  184.760241]  [<ffffffff813c7909>] ? ia32_do_call+0x13/0x13

No Linux Kernel source modifications required

This is important for a number of reasons -- unless dtrace is accepted into the kernel, it has to live with changes to header files and data structures. Also, from a licensing perspective it is not valid for dtrace to touch your sources. It is also much easier to not even require kernel sources - so long as a kernel build environment is available.

INSTALLATION

Run make with no arguments to see the current options. You may need to run one of the tools/get-deps scripts for your OS flavor to ensure you have the tools and kernel build environment for your kernel.

make all
    to compile the drivers and user space commands. Check the file
    Packages, for hints on what you need (not much, but libelf, kernel
    source, flex/yacc -- bison will do).

make install
    Copy dtrace binary and driver to correct install location.

make load
    To load the drivers, and then you can play with cmd/dtrace/dtrace.

make unl
    to unload the drivers.

make test
    To run the userland cmd/dtrace regression test

To build the userland (command and object file etc) and the kernel module for different architectures, set the environment variable BUILD_ARCH appropriately and then use the make targets separately.

This example is for building on a system with a 64-bit kernel, but with 32-bit userland:

   BUILD_ARCH=i386 make cmds
   BUILD_ARCH=x86_64 make kernel

Dependencies

To build dtrace for linux requires a number of tools - mostly the basic Unix development tools, plus you will need the kernel source/build tree. dtrace does not affect or touch your kernel sources, but it needs the normal header files for creating a loadable module.

Examine the following scripts to help identify missing packages:

tools/get-deps-arch.sh
tools/get-deps-fedora.sh
tools/get-deps.pl

Internet scripts

Many scripts on the 'Net won't work since they tend to assume a Solaris kernel, but if you look at them and read them to learn, then they can mostly be adapted for Linux.