112 lines
4.2 KiB
Markdown
112 lines
4.2 KiB
Markdown
This page describes the process of obtaining diagnostic information
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from SeaBIOS and for reporting problems.
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Diagnostic information
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======================
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SeaBIOS has the ability to output diagnostic messages. This is
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implemented in the code via calls to the "dprintf()" C function.
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On QEMU these messages are written to a special debug port. One can
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view these messages by adding '-chardev stdio,id=seabios -device
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isa-debugcon,iobase=0x402,chardev=seabios' to the QEMU command line.
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Once this is done, one should see status messages on the console.
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On coreboot these messages are generally written to the "cbmem"
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console (CONFIG_DEBUG_COREBOOT). If SeaBIOS launches a Linux operating
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system, one can obtain the cbmem tool from the coreboot repository and
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run "cbmem -c" to view the SeaBIOS diagnostic messages.
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Additionally, if a serial port is available, one may compile SeaBIOS
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to send the diagnostic messages to the serial port. See the SeaBIOS
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CONFIG_DEBUG_SERIAL option.
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Trouble reporting
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=================
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If you are experiencing problems with SeaBIOS, it's useful to increase
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the debugging level. This is done by running "make menuconfig" and
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setting CONFIG_DEBUG_LEVEL to a higher value. A debug level of 8 will
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show a lot of diagnostic information without flooding the serial port
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(levels above 8 will frequently cause too much data).
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To report an issue, please collect the serial boot log with SeaBIOS
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set to a debug level of 8 and forward the full log along with a
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description of the problem to the SeaBIOS [mailing list](Mailinglist).
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Timing debug messages
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=====================
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The SeaBIOS repository has a tool (**scripts/readserial.py**) that can
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timestamp each diagnostic message produced. The timestamps can provide
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some additional information on how long internal processes take. It
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also provides a simple profiling mechanism.
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The tool can be used on coreboot builds that have diagnostic messages
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sent to a serial port. Make sure SeaBIOS is configured with
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CONFIG_DEBUG_SERIAL and run the following on the host receiving serial
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output:
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`/path/to/seabios/scripts/readserial.py /dev/ttyS0 115200`
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Update the above command with the appropriate serial device and baud
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rate.
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The tool can also timestamp the messages from the QEMU debug port. To
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use with QEMU run the following:
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```
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mkfifo qemudebugpipe
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qemu -chardev pipe,path=qemudebugpipe,id=seabios -device isa-debugcon,iobase=0x402,chardev=seabios ...
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```
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And then in another session:
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`/path/to/seabios/scripts/readserial.py -nf qemudebugpipe`
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The mkfifo command only needs to be run once to create the pipe file.
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When readserial.py is running, it shows a timestamp with millisecond
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precision of the amount of time since the start of the log. If one
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presses the "enter" key in the readserial.py session it will add a
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blank line to the screen and also reset the time back to zero. The
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readserial.py program also keeps a log of all output in files that
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look like "seriallog-YYYYMMDD_HHMMSS.log".
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Debugging with gdb on QEMU
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==========================
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One can use gdb with QEMU to debug system images. To do this, add '-s
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-S' to the QEMU command line. For example:
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`qemu -bios out/bios.bin -fda myfdimage.img -s -S`
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Then, in another session, run gdb with either out/rom16.o (to debug
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bios 16bit code) or out/rom.o (to debug bios 32bit code). For example:
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`gdb out/rom16.o`
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Once in gdb, use the command `target remote localhost:1234` to have
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gdb connect to QEMU. See the QEMU documentation for more information
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on using gdb and QEMU in this mode.
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When debugging 16bit code it is necessary to load the 16bit symbols
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twice in order for gdb to properly handle break points. To do this,
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run the following command `objcopy --adjust-vma 0xf0000 out/rom16.o
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rom16offset.o` and then run the following in gdb:
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```
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set architecture i8086
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add-symbol-file rom16offset.o 0
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```
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To debug a VGA BIOS image, run `gdb out/vgarom.o`, create a
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vgaromoffset.o file with offset 0xc0000, add use the gdb
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command `add-symbol-file out/vgaromoffset.o 0` to load the 16bit VGA
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BIOS symbols twice.
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If debugging the 32bit SeaBIOS initialization code with gdb, note that
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SeaBIOS does self relocation by default. This relocation will alter
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the location of initialization code symbols. Disable
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CONFIG_RELOCATE_INIT to prevent SeaBIOS from doing this.
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