Add qemu 2.4.0

[kvmfornfv.git] / qemu / roms / seabios / docs / Debugging.md

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