sparc64/93226: DEBUG_LOCKS (really stack_save()) causes panics on sparc64

Antoine Brodin antoine.brodin at
Mon Feb 13 12:37:21 PST 2006

John Baldwin <jhb at> wrote:
> On Monday 13 February 2006 13:36, Antoine Brodin wrote:
> > John Baldwin <jhb at> wrote:
> > > If there are kernel functions before the assembly ones (dependent on link
> > > order) then this would wrongly bail when it hit those.  I think you need
> > > to do what the ddb stack tracing code does which is to lookup the symbol
> > > name and do a bcmp() on the first 4 chars to recognize trapframes.
> >
> > I ran objdump -d on a sparc64 kernel and it looks like tl0_* and tl1_*
> > are always at the beginning of the code, there is some kind of magic.
> magic aside, it would be best to use the same algorithm in both places IMO.  
> It would also be a lot more intuitive to other folks later on.

There are 2 reasons why I didn't use db_search_symbol() and
db_symbol_values() :

- first they aren't reentrant, they use a global variable
db_last_symtab and they can panic if a thread sets db_last_symtab to 0
while another one is using it. I found this in my mail archive :
Stopped at      X_db_symbol_values+0x18:        cmpl    $0,0xc(%eax)
db> trace
Tracing pid 34983 tid 100093 td 0xc2e9c640
X_db_symbol_values(0,c0738214,e84859f4,e84859c4,7c) at X_db_symbol_values+0x18
db_symbol_values(c0738214,e84859f4,0,c89d19c8,0) at db_symbol_values+0x40
It can be fixed easily but I don't have the fix anymore.
You can use linker_ddb_search_symbol() and linker_ddb_symbol_values() 
too that are safer.

- the second reason is performance. if you replace 
CTRSTACK(KTR_LOCK, &stack, 0, 1);
CTRSTACK(KTR_LOCK, &stack, 0, 0);
in kern_lock.c, i.e. if you print the symbol name in the ktr traces, you
will notice that your box is extremely slow. (you type ls, you wait 4 or 5
seconds and you have the result)



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