gdb and OpenJDK

[Andrew Haley]

On 02/16/2015 12:06 PM, Erik Helin wrote:
> On 2015-02-16, Andrew Haley wrote:
>> On 02/16/2015 10:43 AM, Volker Simonis wrote:
>>> Now if we replicate this SA code one more time in a Python library for
>>> GDB, you'll probably agree that it can't work more reliably than the
>>> original SA code. This may be good enough for some use cases, but it
>>> won't be perfect. I'm not a gdb/DWARF expert but I think what we
>>> really need is to generate debug information for all the generated
>>> code. We need to know for every single PC of generated code the
>>> corresponding frame information and how to get to the previous frame.
>>
>> It would be nice.  We don't actually need it, given that we've done
>> without for years, and generating e.g. full DWARF unwinder data for
>> every instruction is something that even GCC doesn't always attempt to
>> do.  (And, of course, there's a lot of hand-written assembly code in
>> HotSpot.  Annotating this is a significant effort.)
> 
> Do we really need to use DWARF though? The gdbjit interface seems to
> support a custom debug format if you also implement a reader for
> your custom debug format. I've never done this, so I can't say if
> there is something missing from the gdbjit API that HotSpot requires.

Well, it would have to be able to convey the same information as DWARF
unwinder data; the GDB people tell me that generating some DWARF is
the right way to do it.  But of course I'm not wedded to any
particular format.

Andrew.