Re: [RFA/RFT PATCH 0/3] Add TDB regset support

[Andreas Arnez <arnez@linux.vnet.ibm.com>]

Pedro Alves <palves@redhat.com> writes:

> On 06/07/2013 07:15 PM, Andreas Arnez wrote:
>> Pedro Alves <palves@redhat.com> writes:
>>> You might not need to look at the auxv.  Return the right tdesc
>>> depending on presence of bfd sections.  See
>>> ppc_linux_core_read_description.
>> 
>> This doesn't work for the TDB, because the absence of the TDB
>> register section doesn't mean that the core file target didn't
>> support it.  At least we'd break the gcore.exp test case.
>
> Okay.  How are the TDB registers presented to the user (info
> all-registers, etc) in the current patchset when the target supports
> them, but the inferior is presently interrupted outside a transaction,
> with live debugging?  (screenshot, please! :-))

(gdb) info all-reg
pswm           0x705200180000000	505845723963588608
pswa           0x8000060a	2147485194
--- /snip/ ---
tdb0           *value not available*
tac            *value not available*
tct            *value not available*
atia           *value not available*
tr0            *value not available*
tr1            *value not available*
tr2            *value not available*
tr3            *value not available*
tr4            *value not available*
tr5            *value not available*
tr6            *value not available*
tr7            *value not available*
tr8            *value not available*
tr9            *value not available*
tr10           *value not available*
tr11           *value not available*
tr12           *value not available*
tr13           *value not available*
tr14           *value not available*
tr15           *value not available*
pc             0x8000060a	0x8000060a <terminal_func+10>
cc             0x2	2

When there's no TDB for the current inferior's state, "value not
available" is the closest representation I could find in the current
regcache design.  Or maybe there is a better way?

My assumption was that this representation is even acceptable when the
inferior runs on a target without transactional-execution support,
because there's really no difference between a program that *never uses*
transactions and a program that *can not* use transactions.

But I can certainly take a shot at an alternate version of the patch
which introduces new target descriptions "s390x-linux64v2-tx" and
"s390-linux64v2-tx" and selects one of those if the hardware supports
transactions. That's what's being proposed, right?

> The new org.gnu.gdb.s390.tdb target feature needs to be documented,
> btw.

OK, will do that in my updated patch.

> TDB support should be mentioned in NEWS too.

Will do.

> With xi:include, that's really pretty manageable.  Please do take a
> look at ppc_linux_read_description and at features/rs6000/, for
> example, though there are several others in the tree.  The x86 port
> has a complex selection of proper description/register set too, given
> xsave.

Did you want to hint at anything specific?  Or just how to add a new
tdesc in general (and select it)?