[Crash-utility] Extensions: Dump log buffer of Intel Processor Trace

[Takao Indoh]

Hi Dave,

The attached files are extension module to dump log buffer of Intel
Processor Trace from vmcore. Please consider placing this in the
extensions page.

[Overview of PT]
PT(Processor Trace) is a new feature of Intel CPU "Broadwell", it
captures information about program execution flow.[1]

Once Intel PT is enabled, the events which change program flow, like
branch instructions, exceptions, interruptions, traps and so on are
logged in the memory. This is very useful for debugging because we can
know the detailed behavior of software.


[About extension]
This extension retrieves log buff of PT from vmcore and saves it as a
file. 'ptdump' command can be used once this extension is loaded.

crash> extend extensions/ptdump.so
./extensions/ptdump.so: shared object loaded
crash> ptdump output_dir
[0] buffer dump: dump.0
[0] packet decode: decode.0
[1] buffer dump: dump.1
[1] packet decode: decode.1
(snipped)

In this case, output_dir directory is created, and then dump.N and
decode.N files are created in the directory for each cpus(N is cpu
number).

dump.N:   raw data of PT
decode.N: result of PT packet decoder

dump.N is binary data and it is not human readable. decode.N is
generated by fastdecode[2], which is PT packet dumper created by Andi
Kleen. It's useful for checking what kinds of packets are included in
dump.N. I'll update extension using PT library(libipt[3]) to generate
more useful file for investigation.

[Build extension]
To build the module from the top-level crash-<version> directory, enter:

$ tar xvf ptdump-1.0.0.tar.gz
$ mv ptdump-1.0.0/* extensions
$ make extensions

[1] https://software.intel.com/en-us/blogs/2013/09/18/processor-tracing
[2] https://github.com/andikleen/simple-pt
[3] https://github.com/01org/processor-trace

Thanks,
Takao Indoh
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