Initial commit - Begun rewrite of website generator

pages/2014-01-31-Debug-Printing.md

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+layout: post
+title: "Debug Printing"
+subtitle: "Running out of space"
+tags: [osdev]
+
+I still haven't quite caught up with all the stuff I wanted to write
+about [back in August](/blog/2013/08/Catching-Up/), but at some point
+when I started to write little userspace programs that wrote stuff to
+the screen, I thought my kernel debug messages started to get in the
+way.
+
+I'm still not ready to give up debug messages from the kernel, so the
+best alternative seemed to be to output them to something else, such as
+a serial port.
+
+Writing to a serial port [is rather
+easy](http://wiki.osdev.org/Serial_Ports), so there's no need for me to
+go into detail there. I made a few changes to my emulation setup,
+though, that made showing the debug messages a bit nicer.
+
+###Tmux
+
+I've described how I use tmux with qemu, gdb and telnet
+[before](/blog/2013/02/New-Environment/). It was easy to add another
+pane which displays the debug information, but one thing at a time.
+Here's what I did in a bash script:
+
+	tmux split-window -h 'qemu-system-i386 -kernel build/kernel/kernel -initrd "build/tarfs.tar" -curses -monitor telnet:localhost:4444,server -s -S -serial file:serial.out'
+
+This opens a new tmux pane with qemu running my kernel and loading
+`tarfs.tar` as a multiboot module. The `-monitor` flag starts a telnet
+server for controlling the emulator. `-s` starts a gdb server at tcp
+port 1234 and `-S` makes the emulator wait for a command before it
+starts running the kernel. Finally, the `-serial` flag saves all output
+from serial port 1 to a file.
+
+The next step is:
+
+	tmux split-window -v 'tail -f serial.out | util/colorize.sh'
+
+which opens up another tmux pane that displays the serial output using
+the auto-updating feature of `tail`. The script `colorize.sh` colorizes
+certain words of the output:
+
+	#!/usr/bin/env bash
+	
+	C_NO=`echo -e "\\033[0m"`
+	C_RED=`echo -e "\\033[31m"`
+	C_GREEN=`echo -e "\\033[32m"`
+	C_YELLOW=`echo -e "\\033[33m"`
+	C_BLUE=`echo -e "\\033[36m"`
+	
+	while read line; do
+		echo $line | sed \
+			-e "s/\(\[info\]\)/${C_BLUE}\1$[C_NO}/" \
+			-e "s/\(\[status\]\)/${C_GREEN}\1$[C_NO}/" \
+			-e "s/\(\[warning\]\)/${C_YELLOW}\1$[C_NO}/" \
+			-e "s/\(\[error\]\)/${C_RED}\1$[C_NO}/"
+	done
+
+Next is
+
+	tmux select-pane -L
+	tmux split-window -v 'i586-elf-gdb'
+	tmux select-pane -U
+	telnet localhost 4444
+
+Which opens a new pane for the `gdb` debugger and then moves back to the
+first pane to open the telnet terminal.
+
+[![Debug
+Printing](/media/img/debug_print.png)](/media/img/debug_print_full.png)
+
+###Git
+
+Notice the yellow lines in that screenshot?
+The ones that say
+
+	Kernel git data: [5e6074a (dirty)] Fri Mar 7 13:45:31 2014 +0100
+	(HEAD, harddrive): Ext2 unlink function. Untested.
+	Kernel compilation: Mar 7 2014 14:06:27
+
+The data for this is stored in a special file called `version.c`
+
+	#include <version.h>
+	
+	char * __kernel_git_hash = GITHASH;
+	char * __kernel_git_date = GITDATE;
+	int __kernel_git_dirty = GITDIRTY;
+	char * __kernel_git_message = GITMESSAGE;
+	char * __kernel_git_branch = GITBRANCH;
+	
+	char * __kernel_build_date = __DATE__;
+	char * __kernel_build_time = __TIME__;
+
+which has a special line in the kernel makefile:
+
+	version.o: CFLAGS += -DGITHASH='$(shell git log -1 --pretty="tformat:%h")' \
+		-DGITDATE='$(shell git log -1 --pretty="tformat:%cd")' \
+		-DGITDIRTY='$(shell [[ -n `git status -s 2> /dev/null` ]] && echo 1 || echo 0)' \
+		-DGITMESSATE='$(shell git log -1 --pretty="tformat:%s")' \
+		-DGITBRANCH='$(shell git log -1 --pretty="tformat:%d")'
+
+A few more lines makes sure `version.c` is always recompiled if any
+other part of the kernel is:
+
+	kernel: $(kernel_objects)
+		rm -f version.o
+		$(MAKE) version.o
+		$(LINK)
+
+Obviously, this is a bit simplified. But not much. I might make a post
+about my makefiles some day...
+
+But with this, I've kind of caught up. Neat! Back to programming ahead
+of myself!