ACRN Debugging Tools

This document describes how to use ACRN tools to collect log and trace data for debugging.

ACRN Console Command

The ACRN console provides shell commands for a user to check system states and environment settings. See the ACRN Shell Commands documentation for a full list of commands, or see a summary of available commands by using the help command within the ACRN shell.

An example

As an example, we’ll show how to obtain the interrupts of a passthrough USB device.

First, we can get the USB controller BDF number (0:15.0) through the following command in the Service VM console:

lspci | grep "USB controller"
../_images/debug_image19.png

Figure 117 USB controller BDF information

Second, we use the pt command in the ACRN console, and use this BDF number to find the interrupt vector (VEC) “0x31”.

../_images/debug_image20.png

Figure 118 USB controller interrupt information

Finally we use the int command in the ACRN console, and use this interrupt vector to find the interrupt number (909) on CPU3.

../_images/debug_image21.png

Figure 119 USB controller interrupt number information

ACRN Log

ACRN log provides a console log and a mem log for a user to analyze. We can use console log to debug directly, while mem log is a userland tool used to capture an ACRN hypervisor log.

Turn on the logging info

ACRN enables a console log by default.

To enable and start the mem log:

$ systemctl enable acrnlog
$ systemctl start acrnlog

Set and grab log

We have six (1-6) log levels for console log and mem log. The following functions print different levels of console log and mem log:

pr_dbg("debug...level %d", LOG_DEBUG);       //level 6
pr_info("info...level %d", LOG_INFO);        //level 5
pr_warn("warn...level %d", LOG_WARNING);     //level 4
pr_err("err...level %d", LOG_ERROR);         //level 3
pr_acrnlog("acrnlog...level %d", LOG_ACRN);  //level 2
pr_fatal("fatal...level %d", LOG_FATAL);     //level 1

If the built-in logging doesn’t provide enough information, you can add additional logging in functions you want to debug, using the functions noted above. For example, add the following code into function shell_cmd_help in the source file acrn-hypervisor/hypervisor/debug/shell.c:

../_images/debug_image22.png

Figure 120 shell_cmd_help added information

Once you have instrumented the code, you need to rebuild the hypervisor and install it on your platform. Refer to Build ACRN from Source for detailed instructions on how to do that.

We set console log level to 5, and mem log level to 2 through the command:

loglevel 5 2

Then we input help into the ACRN console (this is the command that we have just instrumented with additional log information), and check the log as follows.

../_images/debug_image23.png

Figure 121 console log information

Then we use the command, on the ACRN console:

vm_console

to switch to the Service VM console. Then we use the command:

cat /tmp/acrnlog/acrnlog_cur.0

and we will see the following log:

../_images/debug_image24.png

Figure 122 mem log information

ACRN Trace

ACRN trace is a tool running on the Service VM to capture trace data. We can use the existing trace information to analyze, and we can add self-defined tracing to analyze code that we care about.

Using Existing trace event ID to analyze trace

As an example, we can use the existing vm_exit trace to analyze the reason and times of each vm_exit after we have done some operations.

  1. Run the following Service VM console command to collect trace data:

    # acrntrace -c
    
  2. Check current directory, and confirm the directory contains four trace files:

    # ls
    0 1 2 3
    
  3. Use the command to get a summary of vmexit:

    # acrnalyze.py -i /home/trace/acrntrace/20190219-001529/1 -o vmexit --vm_exit
    

    Note

    The acrnalyze.py script is in the misc/tools/acrntrace/scripts folder. The location of the trace files produced by acrntrace may be different in your system.

    ../_images/debug_image28.png

    Figure 123 vmexit summary information

Using Self-defined trace event ID to analyze trace

For some undefined trace event ID, we can define it by ourselves as shown in the following example:

  1. Add the following new event ID into acrn-hypervisor/hypervisor/include/debug/trace.h:

    ../_images/debug_image25.png

    Figure 124 trace event ID

  2. Add the following format to misc/tools/acrntrace/scripts/formats:

    ../_images/debug_image1.png

    Figure 125 acrntrace formatted information

    Note

    Formats:

    0x00000005: event ID for trace test

    %(cpu)d: corresponding CPU index with decimal format

    %(event)016x: corresponding event id with hex format

    %(tsc)d: corresponding event time stamp with decimal format

    %(1)08x: corresponding first Long data in TRACE_2L

  3. Add trace into function emulate_io in acrn-hypervisor/hypervisor/arch/x86/guest/io_emul.c that we want to trace for the calling times of function emulate_io:

    ../_images/debug_image2.png

    Figure 126 inserted trace information

  4. After we have inserted the trace code addition, we need to rebuild the ACRN hypervisor and install it on the platform. Refer to Build ACRN from Source for detailed instructions on how to do that.

  5. Now we can use the following command in the Service VM console to generate acrntrace data into the current directory:

    acrntrace -c
    
    ../_images/debug_image3.png

    Figure 127 trace collection

  6. Run the console command:

    # acrntrace_format.py \
      formats /home/trace/acrntrace/20190219-001529/1 | grep "trace test"
    

    Note

    The acrnalyze.py script is in the misc/tools/acrntrace/scripts folder. The location of the trace files produced by acrntrace may be different in your system.

    and we will get the following log:

    ../_images/debug_image4.png

    Figure 128 trace collection

    Note

    The trace data may generate on any of the available CPUs, so you’ll need to check which CPU number was used and specify that CPU to analyze its trace.