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[PATCH 0/2][RFC] user space instruction tracing


[PATCH 0/2] Instruction tracing

This patch set provides the tapset required to support user space instruction tracing and is only applicable to the x86 architecture. It exploits the utrace mechanism for doing single-step instruction tracing.

Some language extensions have been discussed on the mailing list but there have been no translator changes made. This patch only deals with the tapset to support instruction tracing. The current proposal is to have the following instruction tracing tapscript syntax:
probe usr_itrace.single_step
or
probe usr_itrace.block_step


The SystemTap translator will generate a trap handler routine for the body of the probe. The body can employ any SystemTap language constructs that doesn't assume
a particular PC context.
The body could use internal variables to distinguish different behavior for different instruction tracing regions.


When the translator sees a single_step or block_step probe, it also inserts
       usr_itrace_init("single_step", trap_handler_address)
               or
       usr_itrace_init("block_step", trap_handler_address)
in the module initialization code.

The current SystemTap support for uprobes is still non-symbolic, but it can be used to turn on/off instruction tracing by making calls to the usr_itrace functions:
usr_itrace_on:long (pid:long) (returns 1=SUCCESS, 0=FAILURE)
usr_itrace_off (pid:long)


The example in [patch 2/2] shows how this can be done.

These patches are against:
2.6.23-rc5      (kernel containing utrace support)
but a RHEL5.1 system should contain all of the necessary kernel support.

Dependencies
systemtap:
I developed against version 0.6/0.129 built 2007-09-24

uprobes:
1. The version of uprobes in systemtap cvs/patches/uprobes/ should still work fine. You can build uprobes into the kernel or as a module. If you want the module version, you need to make sure your kernel has the right exports. See README in that directory.


2. As of 10/08/07, the systemtap cvs view contains a working version of uprobes. You can get a cvs view of systemtap's src directory, and build and install systemtap as described in src/README. Assuming you have a utrace-enabled kernel WITH APPROPRIATE EXPORTS (RHEL 5.1 needs to export access_process_vm), stap will automatically build and insmod uprobes when you run a stap script that uses uprobes. Or you can just
# cd src/runtime/uprobes
# make
# insmod uprobes.ko


TODO:
- add support for instruction tracing child threads
- add support for instruction tracing forked children
- add more useful instruction tracing output routines that can be called from the single step instruction handler
- port to PPC


Summary of patches:
[patch 1/2] usr_itrace.stp
[patch 2/2] User Instruction Tracing Example


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