mandelbratwurst

Last friday, my research accidentally met its goal of finding bugs - or at least, in one very specific case.

I was looking into ways for my code to generate keyboard interrupts+input - it turns out simics has a nice interface in the kbd0.key_event attribute - and testing it by triggering some hard-coded keyboard input when the kernel reaches a particular (also hard-coded) point in the fork() path. the input was "mandelbrot\n", which (being received by the shell) should cause the so-named test to start running - except the input would be repeated when fork() runs again, so the kernel's readline() logic would have to deal with multiple inputted lines while another program is writing to the console at the same time.

Here's what pathos, the 410 reference kernel, does:

And what BrOS, the student kernel of Eric Faust (who is periodically keeping me company and scoffing at my code), does:

Slightly different, and not in agreement with the Pebbles specification, though Eric claims it's misdesigned rather than buggy. Finally, here's what POBBLES, my own student kernel, does:

Note the top-left character - that is where every single character of the mandelbrot fractal is being drawn. Also, the input string (rather, parts thereof) is drawn five times, despite only being issued twice. No "misdesign" would cause that...