[syslinux] Dynamic debugging

[Matt Fleming]

Folks,

I've just pushed a new feature out in 5.11-pre8 that will hopefully aid
in debugging future issues - the ability to dynamically (at runtime)
enable and disable debug code using the new debug.c32 module.

For instance, to turn on the dprintf() in execute(), you'd do,

    debug.c32 -e execute

then, every time a module is executed you'll see messages like,

    kernel is ls.c32, args = /  type = 7

To disable functions,

    debug.c32 -d open_file searchdir put_inode

Chances are that if you report a bug now, you'll be asked to run
debug.c32 with a list of useful debugging functions to help narrow down
the cause of your bug. The hope is that this will reduce debugging time,
especially for those difficult problems that always seem to be
environment-specific.

The majority of uses for now will be to enable dprintf() statements, but
over time expect to see more and more integrity-checking code added to
Syslinux, especially in the network stack where it makes sense to
validate input data much more aggressively for debugging purposes.

My intention is to turn this feature off for releases, but depending on
how useful it ends up being, we may keep it enabled.

-- 
Matt Fleming, Intel Open Source Technology Center