GCJ Thread Dump

Thu Feb 10 18:11:00 GMT 2005

Bryce McKinlay wrote:
> David Daney wrote:
>>>>> The problem I see is that for targets that have no frame pointer. 
>> These have to use the DWARF .eh_frame information for generating 
>> stacktraces. The stop-the-world uses asynchronous signals and these 
>> are not compatible with DWARF exception handling.
>>>> On most platforms, we can unwind through signal handlers thanks to 
> MD_FALLBACK_FRAME_STATE_FOR - this is how NullPointerException is 
> implemented.
>
Indeed I know all about MD_FALLBACK_FRAME_STATE_FOR. The problem is 
that gcc only generates good unwinding data for instructions that can 
fault (ie synchronous signals). In general it does not work for 
asynchronous signals (which are used to stop-the-world) as that would 
require much larger tables.
For some architectures (i.e. MIPS) it is possible to backtrace in most 
circumstances with neither DWARF data or frame pointers. However I 
think that things like ld.so's lazy resolution of dynamic library 
symbols may cause even this technique to fail.
David Daney.