[OpenBIOS] Solaris kmdb support for OpenBIOS SPARC64

[Mark Cave-Ayland]

Hi all,

I've been looking at how to enable kmdb support for Solaris OpenBIOS 
SPARC64 and it seems that OpenBIOS needs some additional routines in 
order for the kernel to load the debugger.

AIUI the kernel makes use of 2 traps for kmdb, for which some searching 
on the internet gives the following:

0x17d : kadb enter
0x17e : kadb breakpoint

Indeed if I start Milax with "boot cdrom:a -kdv" then current SVN trunk 
will halt because the 0x17d trap currently jumps straight to the bug() 
routine. Sadly what OpenBIOS should do is a little more hazy, especially 
as I don't think the relevant sun4u parts are in Sun's open-sourced 
OpenBOOT.

Currently booting Milax will emit the following error on the console 
during boot:

interpret : kmdb_callback   %pc f000.0000 ffff.ffff between if exit then 
   %pc h# 18e9058 x!   %npc h# 18e9060 x!   %g1 h# 18e8f58 x!   %g2 h# 
18e8f60 x!   %g3 h# 18e8f68 x!   %g4 h# 18e8f70 x!   %g5 h# 18e8f78 x! 
  %g6 h# 18e8f80 x!   %g7 h# 18e8f88 x!   1 %tstate h# 18e9220 x!   1 
%tt h# 18e90e8 x!   %tba h# 18e90a8 x!   h# 12f6098 set-pc     go ; 
failed with error ffffffffffffffed
kmdb_callback:interpret: exception -13 caught
interpret  ['] kmdb_callback init-debugger-hook  failed with error 
ffffffffffffffed

Based upon this, my best guess would be that both traps above execute 
the init-debugger-hook word which simply copies the current register 
sets above on PROM entry somewhere accessible to kmdb, then points the 
PC to the debugger entry point and resumes execution causing a jump 
straight into kmdb. Does this sound about right?


ATB,

Mark.