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| --- | ||
| refs/heads/master: 751851af7aae9b8bd5a60b3897209081fbc18b2b | ||
| refs/heads/master: 5a86102248592e178a9023359ccf7f0e489d8e35 |
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| In-kernel memory-mapped I/O tracing | ||
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| Home page and links to optional user space tools: | ||
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| http://nouveau.freedesktop.org/wiki/MmioTrace | ||
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| MMIO tracing was originally developed by Intel around 2003 for their Fault | ||
| Injection Test Harness. In Dec 2006 - Jan 2007, using the code from Intel, | ||
| Jeff Muizelaar created a tool for tracing MMIO accesses with the Nouveau | ||
| project in mind. Since then many people have contributed. | ||
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| Mmiotrace was built for reverse engineering any memory-mapped IO device with | ||
| the Nouveau project as the first real user. Only x86 and x86_64 architectures | ||
| are supported. | ||
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| Out-of-tree mmiotrace was originally modified for mainline inclusion and | ||
| ftrace framework by Pekka Paalanen <pq@iki.fi>. | ||
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| Preparation | ||
| ----------- | ||
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| Mmiotrace feature is compiled in by the CONFIG_MMIOTRACE option. Tracing is | ||
| disabled by default, so it is safe to have this set to yes. SMP systems are | ||
| supported, but tracing is unreliable and may miss events if more than one CPU | ||
| is on-line, therefore mmiotrace takes all but one CPU off-line during run-time | ||
| activation. You can re-enable CPUs by hand, but you have been warned, there | ||
| is no way to automatically detect if you are losing events due to CPUs racing. | ||
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| Usage Quick Reference | ||
| --------------------- | ||
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| $ mount -t debugfs debugfs /debug | ||
| $ echo mmiotrace > /debug/tracing/current_tracer | ||
| $ cat /debug/tracing/trace_pipe > mydump.txt & | ||
| Start X or whatever. | ||
| $ echo "X is up" > /debug/tracing/marker | ||
| $ echo none > /debug/tracing/current_tracer | ||
| Check for lost events. | ||
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| Usage | ||
| ----- | ||
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| Make sure debugfs is mounted to /debug. If not, (requires root privileges) | ||
| $ mount -t debugfs debugfs /debug | ||
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| Check that the driver you are about to trace is not loaded. | ||
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| Activate mmiotrace (requires root privileges): | ||
| $ echo mmiotrace > /debug/tracing/current_tracer | ||
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| Start storing the trace: | ||
| $ cat /debug/tracing/trace_pipe > mydump.txt & | ||
| The 'cat' process should stay running (sleeping) in the background. | ||
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| Load the driver you want to trace and use it. Mmiotrace will only catch MMIO | ||
| accesses to areas that are ioremapped while mmiotrace is active. | ||
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| [Unimplemented feature:] | ||
| During tracing you can place comments (markers) into the trace by | ||
| $ echo "X is up" > /debug/tracing/marker | ||
| This makes it easier to see which part of the (huge) trace corresponds to | ||
| which action. It is recommended to place descriptive markers about what you | ||
| do. | ||
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| Shut down mmiotrace (requires root privileges): | ||
| $ echo none > /debug/tracing/current_tracer | ||
| The 'cat' process exits. If it does not, kill it by issuing 'fg' command and | ||
| pressing ctrl+c. | ||
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| Check that mmiotrace did not lose events due to a buffer filling up. Either | ||
| $ grep -i lost mydump.txt | ||
| which tells you exactly how many events were lost, or use | ||
| $ dmesg | ||
| to view your kernel log and look for "mmiotrace has lost events" warning. If | ||
| events were lost, the trace is incomplete. You should enlarge the buffers and | ||
| try again. Buffers are enlarged by first seeing how large the current buffers | ||
| are: | ||
| $ cat /debug/tracing/trace_entries | ||
| gives you a number. Approximately double this number and write it back, for | ||
| instance: | ||
| $ echo 128000 > /debug/tracing/trace_entries | ||
| Then start again from the top. | ||
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| If you are doing a trace for a driver project, e.g. Nouveau, you should also | ||
| do the following before sending your results: | ||
| $ lspci -vvv > lspci.txt | ||
| $ dmesg > dmesg.txt | ||
| $ tar zcf pciid-nick-mmiotrace.tar.gz mydump.txt lspci.txt dmesg.txt | ||
| and then send the .tar.gz file. The trace compresses considerably. Replace | ||
| "pciid" and "nick" with the PCI ID or model name of your piece of hardware | ||
| under investigation and your nick name. | ||
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| How Mmiotrace Works | ||
| ------------------- | ||
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| Access to hardware IO-memory is gained by mapping addresses from PCI bus by | ||
| calling one of the ioremap_*() functions. Mmiotrace is hooked into the | ||
| __ioremap() function and gets called whenever a mapping is created. Mapping is | ||
| an event that is recorded into the trace log. Note, that ISA range mappings | ||
| are not caught, since the mapping always exists and is returned directly. | ||
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| MMIO accesses are recorded via page faults. Just before __ioremap() returns, | ||
| the mapped pages are marked as not present. Any access to the pages causes a | ||
| fault. The page fault handler calls mmiotrace to handle the fault. Mmiotrace | ||
| marks the page present, sets TF flag to achieve single stepping and exits the | ||
| fault handler. The instruction that faulted is executed and debug trap is | ||
| entered. Here mmiotrace again marks the page as not present. The instruction | ||
| is decoded to get the type of operation (read/write), data width and the value | ||
| read or written. These are stored to the trace log. | ||
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| Setting the page present in the page fault handler has a race condition on SMP | ||
| machines. During the single stepping other CPUs may run freely on that page | ||
| and events can be missed without a notice. Re-enabling other CPUs during | ||
| tracing is discouraged. | ||
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| Trace Log Format | ||
| ---------------- | ||
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| The raw log is text and easily filtered with e.g. grep and awk. One record is | ||
| one line in the log. A record starts with a keyword, followed by keyword | ||
| dependant arguments. Arguments are separated by a space, or continue until the | ||
| end of line. The format for version 20070824 is as follows: | ||
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| Explanation Keyword Space separated arguments | ||
| --------------------------------------------------------------------------- | ||
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| read event R width, timestamp, map id, physical, value, PC, PID | ||
| write event W width, timestamp, map id, physical, value, PC, PID | ||
| ioremap event MAP timestamp, map id, physical, virtual, length, PC, PID | ||
| iounmap event UNMAP timestamp, map id, PC, PID | ||
| marker MARK timestamp, text | ||
| version VERSION the string "20070824" | ||
| info for reader LSPCI one line from lspci -v | ||
| PCI address map PCIDEV space separated /proc/bus/pci/devices data | ||
| unk. opcode UNKNOWN timestamp, map id, physical, data, PC, PID | ||
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| Timestamp is in seconds with decimals. Physical is a PCI bus address, virtual | ||
| is a kernel virtual address. Width is the data width in bytes and value is the | ||
| data value. Map id is an arbitrary id number identifying the mapping that was | ||
| used in an operation. PC is the program counter and PID is process id. PC is | ||
| zero if it is not recorded. PID is always zero as tracing MMIO accesses | ||
| originating in user space memory is not yet supported. | ||
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| For instance, the following awk filter will pass all 32-bit writes that target | ||
| physical addresses in the range [0xfb73ce40, 0xfb800000[ | ||
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| $ awk '/W 4 / { adr=strtonum($5); if (adr >= 0xfb73ce40 && | ||
| adr < 0xfb800000) print; }' | ||
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| Tools for Developers | ||
| -------------------- | ||
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| The user space tools include utilities for: | ||
| - replacing numeric addresses and values with hardware register names | ||
| - replaying MMIO logs, i.e., re-executing the recorded writes | ||
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