[coyotos-dev] The joys of hardware bugs

[Jonathan S. Shapiro]

On Wed, 2007-09-26 at 18:22 -0400, Christopher Nelson wrote:
>         Real hardware at home would run quite a while, and then would
>         assertion
>         check, complaining that the 'user accessable' bit was set in
>         an entry. 
>         This was what finally allowed me to trace the problem down.
> 
> You probably already know this, but bochs has a gdb stub....

Yes. So does qemu. Generally we use qemu, because it is faster.  Bochs
also has a built-in debugger that I contributed some effort to.

> So nice to step through the kernel, examine the memory.  Makes finding
> tricky stuff like this easier. 

Definitely nice, but would not have helped this bug. The debugger
generally relies on the current memory map to perform its memory
references. The problem in this case was that the emulators were not
entirely faithful to the hardware, so the error was being reported very
much later than it actually occurred. This had us looking in the wrong
places.

shap