Single stepping through atomic ops

[Marcel Moolenaar]

Sorry for the delay...
There's an effort to import GDB 6.4 I think. What's the version of GDB  
that is fixed?


-- 
Marcel

On Apr 30, 2009, at 2:01 AM, Rafal Jaworowski <raj at semihalf.com> wrote:

>
> On 2009-04-21, at 19:57, Rafal Jaworowski wrote:
>
>> Hi Marcel,
>> I'm writing to you primarily as the gdb maintainer :-) There's a  
>> problem with current gdb in base when single stepping through  
>> atomic sequences on PowerPC (and presumably other archs with the  
>> load + conditional store approach for atomic ops). The effect is a  
>> hang because we endlessly loop due to the [always] lost reservation  
>> at the time of a closing stwcx.
>>
>> This is a known problem with gdb and it's fixed with newer  
>> versions, but the patches are not applicable to our gdb due to some  
>> infrastructure changes. The quick fix for 6.1.1 is here:
>> http://people.freebsd.org/~raj/patches/powerpc/gdb-ppc-single-step.diff
>>
>> It's mainly a transplant of two fixes from the gdb repository  
>> (1.275, 1.276, deal_with_atomic_sequence) adjusted to our older gdb  
>> code, but it's ugly #ifdef'ed __ppc__. In order to do it cleanly we  
>> would need to change the signature of the SOFTWARE_SINGLE_STEP  
>> method so it returns a value (this is how newer gdb works), but it  
>> would affect gdb for all architectures. Do you see any objections  
>> for growing a return value here?
>>
>> Another direction would be importing a newer gdb code base, and be  
>> able to apply the fixes directly and cleanly (if at all required),  
>> but am not sure if there are any plans to upgrade gdb in base? Let  
>> me know your comments.
>
> Have you got any comments to this? Should I move on and commit this  
> as ugly as is, or would reworking SOFTWARE_SINGLE_STEP be more  
> desired? Any thoughts about newer gdb versions coming to the tree?
>
> Rafal
>